taxonID	type	description	language	source
039D223DFFA6FFF5FC78F9ED62A9F852.taxon	materials_examined	Type species: Spongia botryoides % Ellis and Solander * 1786) % by original designation). Type locality: Harbour near Emsworth * between Sussex and Hampshire * the English Channel. Diagnosis: % Based on: Hooper et al. 2002). Leucosoleniidae * in which the skeleton can consist of diactines * triactines * and / or tetractines. There is no reinforced external layer on the tubes.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFA8FFFFFF68FA406245FE46.taxon	description	(Figs 3 – 6; Table 4) Type material: Not known * probably lost.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFA8FFFFFF68FA406245FE46.taxon	materials_examined	Type locality: British Isles * Devon coast % Montagu 1818). Material studied: Three specimens. Molecular data — three specimens % WS 11661 * WS 11662 * WS 11663) * external morphology — three specimens % WS 11661 * WS 11662 * WS 11663) * skeleton organization — one specimen % WS 11662) * spicules % SEM) — three specimens % WS 11661 * WS 11662 * WS 11663) * cytology % TEM) — three specimens % WS 11661 * WS 11662 * WS 11663) % Supporting Information * Table S 1).	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFA8FFFFFF68FA406245FE46.taxon	description	External morphology: Cormus more or less spherical * bearing multiple * erect * oscular tubes with short * lateral diverticula in basal part % Fig. 3 A). Prominent perioscular spicular crown absent % Fig. 3 B). Surface minutely hispid. Coloration of living and preserved specimens greyish white % Fig. 3 A). Spicules: Diactines % Fig. 4 A – C). Two populations: % i) curved lanceolate diactines % Fig. 4 A) * mean length 263.7 µm * mean width 9.5 µm % Table 4) * slightly curved * smooth * with lanceolate outer tip * variable in length and % ii) trichoxeas % Fig. 4 B) * mean length 127.3 µm * mean width 2.4 µm % Table 4) * thin * straight * narrowing toward outer end * both ends pointed * not lance-shaped. Numerous irregularly distributed spines * number and size of spines decrease toward inner end % Fig. 4 C). Triactines % Fig. 4 D). Predominantly parasagittal V-shaped % mean angle 125.7 °) * with unpaired actines usually longer than paired % mean length: 113.5 µm — unpaired * 94.9 µm — paired) % Table 4) * but equal and shorter unpaired actines also occur. Unpaired actines usually slightly slender than paired % mean width: 6.3 µm — unpaired * 6.8 µm — paired) % Table 4). T-shaped sagittal triactines absent. Tetractines % Fig. 4 E). Predominantly parasagittal V-shaped % mean angle 123.5 °). Unpaired actines usually longer than paired * rarely equal % mean length: 109.3 µm — unpaired * 93.9 µm — paired * 23.8 µm — apical) % Table 4). Paired and unpaired actines equal in width * apical actine more slender % mean width: 6.7 µm — unpaired * 6.9 µm — paired * 5.3 µm — apical) % Table 4). Apical actine curved and smooth. Skeleton: Skeleton of both oscular and cormus tubes predominantly formed by tetractines; triactines quite rare % Fig. 3 C * D). In oscular tubes * spicules constitute organized array with their unpaired actines directed toward cormus and oriented more or less in parallel to proximo-distal axis of oscular tube % Fig. 3 C). In cormus tubes * spicule array less organized % Fig. 3 D). Lanceolate diactines cover tubes’ surface * orienting in different directions and extending outside by lance-shaped tip. Trichoxeas sparsely distributed on outer surface. No prominent spicular crown on oscular rim % Fig. 3 B). Cytology: Body wall * 6 – 9 µm thick * three layers: exopinacoderm * loose mesohyl * and choanoderm % Fig. 5 A * B; Supporting Information * Table S 2). Flat endopinacocytes located in only distal part of oscular tube % oscular ring) replacing choanocytes. Inhalant pores scattered throughout exopinacoderm * except the oscular ring area. Exopinacocytes non-flagellated T-shaped * rarely flat % Fig. 5 C). External surface covered by glycocalyx. Cell body % height 4.8 µm * width 2.8 µm) * containing nucleus % diameter 2.2 µm) * submersed in mesohyl % Fig. 5 C). Cytoplasm with specific spherical electron-dense inclusions % 0.3 – 0.4 µm diameter) % Fig. 5 C). Endopinacocytes non-flagellated flat cells * size 20 – 30 µm × 2 – 2.5 µm % Fig. 5 D). External surface covered by glycocalyx. Nucleus % 2.4 × 1.8 µm) oval with or without nucleolus. Cytoplasm without specific inclusions % Fig. 5 D). Choanocytes flagellated trapeziform or prismatic % height 6 µm * width 3.7 µm) % Fig. 5 E). Flagellum surrounded by collar of microvilli. Characteristic pyriform nucleus % diameter 2.3 µm) in apical position. Cytoplasm with phagosomes and small vacuoles % Fig. 5 E). Porocytes tubular cylindrical % height 4.5 µm * width 2 µm) * connecting external milieu with choanocyte tube % Fig. 5 B * F). Nucleus oval to spherical * diameter 1.8 µm * sometimes with nucleolus. Cytoplasm with phagosomes and small vacuoles % Fig. 5 F). Sclerocytes amoeboid * size 4 µm × 2 µm % Fig. 6 A). Nucleus usually oval or pear-shaped % diameter 1.6 µm) * containing single nucleolus. Well-developed Golgi apparatus and rough endoplasmic reticulum. Cytoplasm usually with phagosomes and / or lysosomes % Fig. 6 A). Amoebocytes of different shape % from oval to amoeboid) without special inclusions * size 5.8 µm × 3.4 µm % Fig. 6 B). Nucleus spherical % diameter 2.2 µm) * sometimes with nucleolus. Two morphotypes of bacterial symbionts in mesohyl. Morphotype 1 most abundant. Bacteria large * rod-shaped * slightly curved * diameter 0.3 µm * length 2.2 µm % Fig. 6 C). Double-cell wall * cytoplasm transparent * nucleoid region filamentous. Morphotype 2 rare. Bacteria rod-shaped * diameter 0.18 µm * length 1.2 µm % Fig. 6 D). Double-cell wall * cytoplasm transparent * nucleoid region filamentous. Distribution: Boreal species. Molecular species identity confirmed for specimens from France % Roscoff). Live in low intertidal and subtidal zones up to 20 m depth * on rocks and kelps % Borojevic et al. * 1968). Reproduction: The specimens collected in February 2017 in Roscoff contained oocytes at the early stages of development. Remarks: Leucosolenia complicata was one of the most undoubted species described in the 19 th century. According to our data * it shows stable internal characters and easily diagnosable external features * i. e. erect multiply oscular tubes extending from the small cormus. The species’ identity and validity of L. complicata are strongly supported by our molecular data as well. It represents a distinct monophyletic lineage on all phylogenetic trees * and p- distance values to other Leucosolenia species are very high % more than 5 % in LSU and 3.8 % in SSU). Extensively studied morphology allows clarification of the species diagnosis * which varied from author to author % Haeckel 1872 * Minchin 1904 * Jones 1954 * Rapp 2015): small cormus * erect multiple oscular tubes * two populations of diactines % curved lanceolate diactines and small trichoxea) * parasagittal tri- and tetractines with predominately longer unpaired actines * skeleton of tubes predominately formed by tetractines. Leucosolenia complicata is easily differentiated from other Leucosolenia species % Leucosolenia variabilis * L. somesii * and others) in these traits. In addition * the mesohyl cell composition of L. complicata is very poor compared to other studied Leucosolenia species: the mesohyl contains only sclerocytes and amoebocytes % Supporting Information * Table S 2). The composition of symbiotic bacteria % two morphotypes of rod-shaped bacteria) differs in L. complicata from L. corallorrhiza and L. variabilis % Supporting Information * Table S 2). 888 • Lavrov et al. Although the type material of this species is not available * if it ever existed * we studied spicule slides from Minchin’s type collections % BMNH 1910.1.1.415 a and BNMH 1910.1.1.435. Aa). They are listed as the type material of L. complicata in the BMNH collection. These slides contain handwritten information on the corresponding paragraphs in Minchin % 1904) with relevant collection information % slides nos. 1 * 2; Minchin 1904: 372). Accordingly * both slides appeared from Canon Normans’s Collection. The specimen BMNH 1910.1.1.415 a was collected at Scarborough % the North Sea) by Bean and sent to Haeckel for examination. The specimen BNMH 1910.1.1.435. Aa was collected at the Guernsey Islands % the English Channel) by J. Bowerbank and probably represents a syntype of Ascandra contorta % Bowerbank * 1866). According to Minchin % 1904) * this slide contains an admixture of L. complicata spicules with A. contorta. All this indicates that slides BMNH 1910.1.1.415 a and BNMH 1910.1.1.435. Aa are not the type material of L. complicata * and the label ‘ type’ probably refers to the Minchin’s type collection * which contained most typical specimens. Since no type material exists * the designation of neotype is needed once the material from the type locality % British Isles * Devon coast) becomes available for molecular study. Ascandra pinus Haeckel * 1872 and Leucosolenia fabricii Schmidt * 1869 are regarded herein as minor synonyms. Ascandra pinus lacks small trichoxeas * which were most probably overlooked by Haeckel % Minchin 1904) * and in Leucosolenia fabricii * the skeleton is formed mostly by triactines * which was considered intraspecific variation by many authors % Minchin 1904 * Burton 1963 * Rapp 2015). However * our data show that these characters may be regarded as diagnostic interspecific features * as shown for the L. variabilis species complex % see below); therefore * both of these species names should be taken into account for future research on European Leucosolenia. Our data also suggest the absence of L. complicata in the White Sea. In works by Breitfuss % 1898 a) * three Leucosolenia species were found at different localities in the White Sea and are described under the names Ascandra variabilis Haeckel * 1872 * Ascandra contorta % Bowerbank * 1866) * and Ascandra fabricii % Schmidt * 1869). Minchin % 1904) later considered the latter two species sensu Breitfuss % 1898 a) as minor synonyms of Leucosolenia complicata due to external morphological characters * while spicular characters were ignored in most cases. However * Ascandra contorta sensu Breitfuss % 1898 a) possesses tri- and tetractines with short * unpaired actines * which is most likely a diagnostic feature for L. variabilis. Due to the absence of L. complicata in our material from the White Sea * and uncertainties in previous research * more material is required from different localities in the White and Barents Seas to clarify the distribution ranges of this species in Arctic waters.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFACFFE2FC27FE42624FFA23.taxon	description	(Figs 7 – 10; Table 5)	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFACFFE2FC27FE42624FFA23.taxon	materials_examined	Type material: Type material is not known. Type locality: Haeckel based his description on one specimen from Norway and one from Greenland * without designating the type material % Rapp 2015). Material studied: Altogether 177 specimens. Molecular data — 177 specimens * external morphology — 177 specimens * skeleton organization — two specimens % WS 11650 * WS 11653) * spicules % SEM) — five specimens % WS 11649 * WS 116450 * WS 11653 * WS 11657 * WS 11658) * cytology % TEM) — six specimens % WS 11631 * WS 11632 * WS 11634 * WS 11635 * WS 11636 * WS 11637) % Supporting Information * Table S 1).	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFACFFE2FC27FE42624FFA23.taxon	description	External morphology: Cormus formed by basal reticulation of tubes * from which erect oscular tubes and long diverticula arising. Sponge bear from one to multiple * slightly curved oscular tubes * with or without short * lateral diverticula in the basal part. Oscular tubes gradually narrow to oscular rim * possessing short * spicular crown % Fig. 7 A * B). Surface minutely hispid or echinate. Coloration of living and preserved specimens greyish white % Fig. 7 A). Spicules: Diactines % Fig. 8 A * B). Curved * lanceolate diactines * mean length 179 µm * mean width 6 µm % Table 5) * slightly curved with lanceolate outer tip * variable in size * smooth or with few small spines at lanceolate tip % Fig. 8 B). Triactines % Fig. 8 D). T-shaped sagittal % mean angle 142.9 °) * unpaired actines usually shorter than paired % mean length: 70.5 µm — unpaired * 82.7 µm — paired) % Table 5) * rarely equal. Actines equal in width % mean width: 6.5 µm — unpaired * 6.5 µm — paired) % Table 5). Tetractines % Fig. 8 C). T-shaped sagittal % mean angle 151.4 °) * unpaired actines shorter than paired or equal % mean length: 68.8 µm — unpaired * 80.7 µm — paired * 22.9 µm — apical) % Table 5). All actines equal in width % mean width: 5.6 µm — unpaired * 5.8 µm — paired * 5.5 µm — apical) % Table 5). Apical actine curved and smooth. Skeleton: Skeleton of oscular tubes predominantly formed by both tri- and tetractines * while in cormus tubes tetractines rare % Fig. 7 C * D). In oscular tubes * spicules constitute organized array with their unpaired actines directed toward cormus and oriented more or less in parallel to proximo-distal axis of oscular tube % Fig. 7 C). In cormus tubes * spicule network appears completely disordered % Fig. 7 D). Both populations of diactines forming small oscular crown up to 60 µm and cover tubes’ surface * orienting in different directions and extending outside by lance-shaped tip % Fig. 7 B). Cytology: Body wall * 8.4 – 12 µm thick * three layers: exopinacoderm * loose mesohyl * and choanoderm % Fig. 9 A * B; Supporting Information * Table S 2). Flat endopinacocytes located only in the distal part of oscular tube % oscular ring) replacing choanocytes. Inhalant pores scattered throughout exopinacoderm * except the oscular ring area. Exopinacocytes non-flagellated * T-shaped * rarely flat % Fig. 9 C). External surface covered by glycocalyx. Cell body % height 7 – 10.5 µm * width 4.3 – 5.5 µm) * containing spherical to oval nucleus % diameter 3.1 µm) * submersed in mesohyl. Cytoplasm with specific spherical electron-dense inclusions % 0.2 – 0.4 µm diameter) % Fig. 9 C). Endopinacocytes non-flagellated flat cells * size 16.8 µm × 2.2 µm % Fig. 9 D). External surface covered by glycocalyx. Nucleus % 2.1 µm × 1.6 µm) spherical to oval with nucleolus. Cytoplasm with specific spherical electron-dense inclusions % 0.2 – 0.5 µm diameter) % Fig. 9 D). Choanocytes flagellated trapeziform or prismatic % height 8.2 µm * width 4.1 µm) % Fig. 9 E). Flagellum surrounded by collar of microvilli. Characteristic pyriform nucleus % 2.6 µm × 4.1 µm) in apical position. Cytoplasm with phagosomes and small vacuoles. Choanocytes united by specialized intercellular contacts similar to septate junctions * but has no basal membrane % Fig. 9 E). Porocytes tubular cylindrical % height 5.5 µm * width 4.2 µm) * connecting external milieu with choanocyte tube % Fig. 9 F). Nucleus pyriform % diameter 3.1 µm) * containing nucleolus. Cytoplasm with phagosomes * small vacuoles * and spherical electron-dense inclusions identical with inclusions of exopinacocytes. Sclerocytes amoeboid * size 8.7 µm × 3.5 µm % Fig. 10 A). Nucleus usually oval or pear-shaped % diameter 2.5 µm) * containing single nucleolus. Well-developed Golgi apparatus and rough endoplasmic reticulum. Cytoplasm usually with phagosomes and / or lysosomes. During spicules’ secretion * sclerocytes form groups of three to six cells * connected by septate junctions % Fig. 10 A). Amoebocytes of different shape % from oval to amoeboid) without special inclusions * size 5.7 µm × 4.7 µm % Fig. 10 B). Nucleus spherical % diameter 2.9 µm) * sometimes with nucleolus. Granular cells oval * size 9 µm × 5.5 µm. Regularly distributed * numerous cells * usually located under choanocytes % Fig. 10 C – E). Nucleus in peripheral position * spherical % diameter 2.5 µm). Cytoplasm with oval * electron-dense inclusions % size 0.9 – 2.7 µm × 1.1 – 3.7 µm) % Fig. 10 E). Inclusion content homogenous or granulated. Often found in stage of degradation * cytoplasm completely filled with two to four large * oval inclusions * with highly osmiophilic granulated content % Fig. 10 F). Myocytes are fusiform cells * size 22 µm × 2.7 µm; distributed in the mesohyl mostly in the oscular ring. Nucleus usually oval % 2.9 µm × 1.6 µm) * without nucleolus % Fig. 10 G). Cytoplasm includes mitochondria * ribosomes * small vesicles * and * most importantly * the presence of cytoplasmic myofilaments of 19 – 12 nm in diameter % Fig. 10 G). Myofilaments form bundles % 0.37 – 0.16 µm diameter) that are located along the long axis of the cell. One morphotype of bacterial symbionts in mesohyl. Bacteria numerous * rod-shaped with double-cell wall * diameter 0.3 – 0.33 µm * length 3.0 – 5.6 µm % Figure 10 H * I). Nucleoid region electron-dense with irregular network of filaments. Distribution: Boreal-Arctic species. Molecular identity confirmed for Greenland and the White Sea % Alvizu et al. 2018). In the White Sea * it is the most abundant species * inhabiting kelps and hard substrates in low intertidal and subtidal zones up to 15 – 20 m depth. Reproduction: In the White Sea * specimens collected in late October contained early oocytes; specimens collected in January / February contained fully developed larvae. Remarks: In the White Sea * this species was initially identified as Leucosolenia variabilis * based on its external morphology % Lavrov et al. 2018). In addition * most of our sequences for this species were identical to LSU and SSU sequences downloaded from the GenBank under the name L. variabilis. Regarding morphology * the spicular characters of our specimens were different from the original description of L. variabilis % Haeckel 1872) * but partly fit the description given in Minchin % 1904). The main differences relate to diactine morphology: in our specimens * there is a single type of curved lanceolate diactines. In L. variabilis sensu Haeckel % 1872) * two diactine populations were found: the first has small * strait trichoxea * and the second has normal * curved * lanceolate diactines. Minchin % 1904) found connectivity in size among small and long diactines * and suggested that they represented a single type of diactine * which was overlooked by Haeckel. Since our specimens possess only a single diactine population * it might support Minchin’s conclusions. However * Leucosolenia variabilis sensu Minchin % 1904) is a species complex * since he designated Leucosolenia somesii a junior synonym of L. variabilis * while morphological and molecular data supported its identity as a distinct species % see below; see also: van Soest et al. 2007). Therefore * the diagnosis provided by Minchin % 1904) should not be taken into consideration. To address the possible ontogenetic variation of diactines * we studied the type material L. variabilis from the collection of BMNH % syntype BMNH- 1910.1.1.421). The spicular characters of this specimen perfectly fit the original description made by Haeckel % 1872) * with two diactine types * tri- and tetractines of equal abundance * and unpaired actines in tri- and tetractines always shorter than paired ones. On the other hand * specimens in our material possess only a single diactine type * and tetractines are rare. Therefore * the species from the White Sea is not L. variabilis * despite its molecular similarity to specimens * placed in the GenBank under the name L. variabilis. Another species * that is characterized by a single diactine type and short unpaired actines in tri- and tetractines is Leucosolenia corallorrhiza * which was designated a valid species in the most recent morphology-based revision of Greenland calcareous sponges % Rapp 2015). Haeckel % 1872) described this species under the name Ascortis corallorrhiza * addressing a small proportion or absence of tetractines * small and thick triactines with short * unpaired actines. Diactines are curved * lance-shaped % Haeckel 1872: 74). This feature is characteristic of samples from the White Sea * although in our specimens * some diactines bear small spines on their lance-shaped tips. These spines are hardly visible with light microscopy and may be overlooked * even during SEM studies. Since we could not study the morphology of specimens whose sequences were obtained from GenBank * and morphological data for those specimens are absent in the respective paper % Alvizu et al. 2018) * we designate our specimens from the White Sea as Leucosolenia corallorrhiza * until both morphological and molecular confirmation for specimens from the type localities become available. Also * neotype designation for this species is necessary to establish the type material; specimens for this purpose should be collected in the type locality. It should be mentioned that our specimens demonstrate minor differences in coloration from the original description [L. corallorrhiza is brown according to Haeckel % 1872)]. Also * actines in tri- and tetractines are thicker in the initial description % widths ~ 15 µm in Haeckel 1872; up to 12.5 µm in our material % Table 5); up to 10.7 µm in Rapp 2015) * but this difference may be associated either with ontogenetic or intraspecific variation * or different measurement procedures and equipment. From Leucosolenia variabilis this species differs by spicular characters: in L. variabilis * there are two types of diactine * while there is only one type of diactine in L. corallorrhiza. Leucosolenia corallorrhiza never forms a large * massive cormus. Leucosolenia corallorrhiza also differs from other species in cytological characteristics % Supporting Information * Table S 2): in contrast to L. complicata * the mesohyl of L. corallorrhiza includes not only amoeboid cells * but also rather numerous granular cells * regularly distributed in the body wall; in contrast to L. variabilis * L. corallorrhiza has larger granular cells * no spherulous cells * and only one morphotype of rod-shaped symbiotic bacteria.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB1FFEBFC08FA7A651AFC33.taxon	description	(Figs 11 – 16; Table 6)	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB1FFEBFC08FA7A651AFC33.taxon	materials_examined	Type material: Syntype BMNH- 1910.1.1.421. Other type material is not known. Type locality: Norway * Bergen. Material studied: Forty specimens. Molecular data — 40 specimens * external morphology — 40 specimens * skeleton organization — three specimens % WS 11643 * WS 11708 * WS 11735) * spicules % light microscopy * SEM) — seven specimens % WS 11707 * WS 11714 * WS 11731 * WS 11732 * WS 14637 * WS 14671 * WS 14681) * cytology % TEM) — three specimens % WS 11643 * WS 11644 * WS 11645) % Supporting Information * Table S 1). External morphology: Length of cormus up to 5 cm. Cormus massive * often spherical * otherwise formed by basal reticulation of tubes. Cormus built as reticulation around one or several largest central tubes. Outline of cormus formed by numerous * short diverticula. Largest tubes of cormus always end with oscula. Main oscular tubes large * prominent * erect * bearing many small diverticula * spreadingtotwo-thirdsoftubes’length. Osculartubegraduallynarrows to oscular rim * possessing short spicular crown % Fig. 11 A * B). In addition to main oscula on largest tubes of cormus * smaller oscular tubes usually scattered all over the cormus. Surface minutely hispid. Coloration of living specimens greyish white. Coloration of preserved specimens from greyish white to ochre % Fig. 11 A). Spicules: Diactines % Figs 12 A * 13 * 16 A). Two populations: % i) curved * smooth * lanceolate diactines % Fig. 12 A) * mean length 306.7 µm * mean width 9.8 µm * % Table 6) * slightly curved * smooth * with lanceolate outer tip * variable in length; % ii) trichoxeas % Fig. 13) * thin % mean width 0.9 µm) % Table 6) * with numerous * irregularly distributed spines % Fig. 13 C) * long * but usually represented by fragments of variable length % up to 362.4 µm long) % Table 6). Triactines % Figs 12 B * C * 16 A). Predominantly T-shaped * sagittal % mean angle 138.5 °) * unpaired actines * variable in length: most frequently equal to paired actines * commonly shorter or rarely longer than paired % mean length: 122.3 µm — unpaired * 127.9 µm — paired) % Table 6). Abnormal triactines with one of paired actines undulated also common % Fig. 12 C). Actines equal in width % mean width: 8.1 µm — unpaired * 8.5 µm — paired) % Table 6). Tetractines % Fig. 12 D). Predominantly T-shaped * sagittal % mean angle 142.2 °) * unpaired actines variable in size: equal to * shorter * or longer than paired actines % mean length: 147.6 µm — unpaired * 142.0 µm — paired * 22.8 µm — apical) % Table 6). Unpaired actines usually slightly slender than paired % mean width: 8.5 µm — unpaired * 9.1 µm — paired) % Table 6). Apical actines curved * smooth * and slender % mean width 5.9 µm) % Table 6).	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB1FFEBFC08FA7A651AFC33.taxon	description	Skeleton: Skeleton of both oscular and cormus tubes formed by dense net of tetractines and triactines % Fig. 11 C * D). In oscular tubes * spicules constitute organized array with their unpaired actines directed toward cormus and oriented more or less in parallel to proximo-distal axis of oscular tube % Fig. 11 C). In cormus tubes * spicule array completely disordered % Fig. 11 D). Diactines form small oscular crown up to 100 µm % Fig. 11 B) and cover tubes’ surface * orienting in different directions and extending outside by lance-shaped tip. Cytology: Body wall * 9 – 13.8 µm thick * three layers: exopinacoderm * loose mesohyl * and choanoderm % Fig. 14 A * B; Supporting Information * Table S 2). Flat endopinacocytes located only in distal part of oscular tube % oscular ring) replacing choanocytes. Inhalant pores scattered throughout exopinacoderm * except the oscular ring area. Exopinacocytes non-flagellated * T-shaped * rarely flat % Fig. 14 C). External surface covered by glycocalyx. Cell body % height 6.3 µm * width 3.7 µm) * containing spherical to oval nucleus % diameter 2.7 µm) * submersed in mesohyl. Cytoplasm with specific spherical electron-dense inclusions % 0.2 – 0.35 µm diameter) % Fig. 14 C). Endopinacocytes non-flagellated * flat cells * size 16 µm × 2.8 µm. External surface covered by glycocalyx. Nucleus % 3.2 µm × 2.3 µm) spherical to oval with nucleolus. Cytoplasm without specific inclusions % Fig. 14 F). Choanocytes flagellated trapeziform or prismatic % height 10.7 µm * width 4.1 µm) % Fig. 14 D). Flagellum surrounded by collar of microvilli. Characteristic pyriform nucleus % diameter 2.5 µm) in apical position. Cytoplasm with phagosomes and small vacuoles % Fig. 14 D). Porocytes tubular cylindrical % height 2.5 – 4.7 µm * width 4.3 – 5 µm) * connecting external milieu with choanocyte tube % Fig. 14 E). Nucleus spherical % diameter 2.7 µm) * containing nucleolus. Cytoplasm with spherical electron-dense inclusions * identical with inclusions of exopinacocytes % Fig. 14 E). Sclerocytes amoeboid * size 6 µm × 3.1 µm % Fig. 15 G). Nucleus usually oval or pear-shaped % diameter 2.2 µm) * containing a single nucleolus. Well-developed Golgi apparatus and rough endoplasmic reticulum. Cytoplasm usually with phagosomes and / or lysosomes % Fig. 15 G). Amoebocytes of different shape % from oval to amoeboid) without special inclusions * size 3 µm × 4 – 7.5 µm % Fig. 15 A). Nucleus spherical % diameter 2.7 µm) * sometimes with nucleolus. Large amoeboid cells of different shape % from elongate to amoeboid) * size 20 µm × 4.2 µm % Fig. 15 B). Rare cells located under choanoderm. Nucleus oval % size 4.8 µm × 1.7 µm). Cytoplasm with numerous * large heterophagosomes % diameter 1.1 – 3.2 µm) * well-developed Golgi apparatus % Fig. 15 B). Granular cells small oval * size 4 µm × 3.3 µm % Fig. 15 C). Rare cell type * located under the choanoderm. Nucleus in peripheral position * spherical % diameter 1.7 µm) with large amounts of heterochromatin * associated with nucleus membrane. Cytoplasm with electron-dense oval inclusions % size 0.7 – 6 µm × 0.4 – 1.1 µm) and rare * spherical * electron-transparent vacuoles % diameter 1.2 µm) % Fig. 15 C). Spherulous cells with irregular shape from amoeboid to crescent * size 2.7 – 9.2 µm × 4.7 – 5.3 µm % Figure 15 E * F). Regularly distributed numerous cells * usually located under choanocytes. Distance between cells 2 – 9 µm % Fig. 15 F). Nucleus deformed % size 2.4 µm × 1.7 µm). Cytoplasm mostly occupied by large crescent or irregular electron-dense homogenous inclusions % diameter 1.8 – 4.5 µm) and less electron-dense fine-granular inclusions % diameter 0.7 – 2.6 µm). Granular or foamy material fills cytoplasm spaces between inclusions % Figure 15 E). Myocytes rare fusiform cells * size 18 µm × 2.7 µm * located in mesohyl % Fig. 15 D). Nucleus oval % 3.5 µm × 2.7 µm) * with nucleolus. Cytoplasm with mitochondria * ribosomes * small vesicles * and cytoplasmic myofilaments. Myofilaments grouped in bundles % diameter 0.07 - 0.2 µm) located along long axis of myocyte % Fig. 15 D). Three morphotypes of bacterial symbionts in mesohyl % Fig. 15 H-J). Morphotype 1 numerous % Fig. 15 H). Bacteria large * spiral-shaped * diameter 0.2 µm * length 2.5 – 3.9 µm. Spiral turns regular and compact. Single-membrane cell wall * cytoplasm granular * nucleoid region tubular % Fig. 15 H). Morphotype 2 rare % Fig. 15 I). Bacteria small * spiral-shaped * diameter 0.3 µm * length 1.5 – 1.8 µm. Spiral turns irregular and sparse. Cytoplasm transparent * nucleoid region tubular % Fig. 15 I). Morphotype 3 rare % Fig. 15 J). Bacteria small * rod-shaped bacteria * diameter 0.23 µm * length 0.8 µm. Double-membrane cell wall * cytoplasm with dark filamentous materials * no distinction between cytoplasm and nucleoid region % Fig. 15 J). Distribution: Boreal-Arctic species * described from Norway. Molecular identity confirmed for the White Sea and Greenland % Alvizu et al. 2018). In the White Sea occurs in low intertidal and subtidal zones up to 40 – 45 m depth * on rocks and kelps. Reproduction: No data about reproduction time for this species. Remarks: We studied three type specimens % slides with spicules) of Leucosolenia variabilis from the British Museum of Natural History % BMNH): BMNH- 1910.1.1.421 * BMNH- 1906.12.1.40 * and BMNH- 1906.12.1.50. Spicules are similar morphologically across these specimens % Fig. 16 B – D) * which supports the idea that they belong to the same species. At the same time * their type status should be reconsidered due to the data represented in the revision by Minchin % 1904). Slide labels contain specific information % exact page and number) * allowing an unambiguous comparison with the collection data of these samples given in Minchin % 1904). Accordingly * BMNH- 1906.12.1.50 was collected from Bantry Bay * Ireland * by C. Norman and identified by him as Leucosolenia botryoides; this label was endorsed by Haeckel ‘ Ascandra variabilis ’ % slide no. 1; Minchin 1904: 385). BMNH- 1906.12.1.40 was received by Haeckel for re-examination from Bowerbank and collected from Guernsey % slide no. 4; Minchin 1904: 385). Finally * BMNH- 1910.1.1.421 was collected by Haeckel in Bergen * Norway * the type locality of this species * and contained a printed label ‘ Ascandra variabilis H’ % slide no. 3; Minchin 1904: 385). Therefore * the slide BMNH- 1910.1.1.421 could be designated as a syntype. The analysis of L. variabilis syntype BMNH- 1910.1.1.421 indicated two diactine types % lanceolate diactines and trichoxeas) * and V- and T-shaped tri- and tetractines with shorter unpaired actines % Fig. 16 D). Although Haeckel’s description lacks long trichoxeas * it should be mentioned that such spicules are easily broken during preparation. It may also be suggested that the second type of diactine without lanceolate tips described by Haeckel % 1872) is in fact broken * long trichoxeas. Direct comparison of spicule slides of specimens from the White Sea with L. variabilis syntype BMNH- 1910.1.1.421 shows strong correspondence between them. Leucosolenia variabilis has a large * massive * sometimes spherical cormus * which could be a good distinctive trait * since all other sympatrically living species % Leucosolenia complicata * L. corallorrhiza * and Leucosolenia sp. A) are represented by basal reticulation of tubes with extended oscular tubes. In spicular characters * L. variabilis differs from L. somesii by the presence of lanceolate spined diactines; and from L. complicata and Leucosolenia sp. A by the presence of extremely long and highly spined trichoxeas. Leucosolenia variabilis also has the highest diversity of mesohyl cells and symbiotic bacteria among the studied Leucosolenia species % Supporting Information * Table S 2). In addition to the usual amoebocytes * L. variabilis also has rare large amoebocytes and small granular cells * as well as numerous unusual spherulous cells of different shapes regularly distributed in the body wall. The composition of symbiotic bacteria of L. variabilis includes three morphotypes: one typical rod-shaped and two unusual spiral-shaped.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB8FFEAFEECFC7666E2F84A.taxon	description	(Figs 17, 18; Table 7)	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB8FFEAFEECFC7666E2F84A.taxon	materials_examined	Material studied: Three specimens. Molecular data — three specimens % WS 11692 * WS 11752 * WS 11770) * external morphology — three specimens % WS 11692 * WS 11752 * WS 11770) * skeleton organization — two specimens % WS 11752 * WS 11770) * spicules % SEM) — two specimens % WS 11692 * WS 11770) % Supporting Information * Table S 1).	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB8FFEAFEECFC7666E2F84A.taxon	description	External morphology: Studied specimens small in size. Length of cormus up to 1 cm. Cormus represented by compact reticulation of tubes * from which several oscular tubes arising. Oscular tubes erect and almost straight. Surface minutely hispid. Coloration of living and preserved specimens greyish white % Fig. 17 A). Spicules: Diactines % Fig. 18 A-C). Two populations: % i) curved * spiny * lanceolate diactines % Fig. 18 B) * mean length 189.1 µm * mean width 7.2 µm % Table 7) * small * from almost straight to slightly curved and undulating * with lanceolate and spiny outer tip * spines in distinct rows % Fig. 18 C); % ii) curved * smooth diactines % Fig. 18 A) * mean length 515.0 µm * mean width 11.6 µm % Table 7) * rare * long * slightly curved * without spines and lanceolate tips % Fig. 18 C). Triactines % Fig. 18 D * E). Predominantly T-shaped * sagittal % mean angle 146.5 °) % Table 7). Unpaired actines variable in size: equal to * shorter * or longer than paired actines * but shorter unpaired actines most common % mean length: 118.5 µm — unpaired * 125.1 µm — paired) % Table 7). Both straight and bent paired actines common. Abnormal triactines in high numbers % Fig. 18 E) * sometimes with undulated actines. Unpaired actines usually slightly slender than paired % mean width: 11.1 µm — unpaired * 11.6 µm — paired) % Table 7). Tetractines % Fig. 18 F). Quite rare. Predominantly T-shaped % mean angle 140.8 °) % Table 7) * variable in size. Unpaired actines equal to paired ones % mean length: 114.3 µm — unpaired * 113.2 µm — paired * 30.0 µm — apical) % Table 7). Unpaired actines straight * paired actines straight or undulating * apical actines curved or undulating * smooth. Paired and unpaired actines equal in width * apical actine more slender % mean width: 8.6 µm — unpaired * 8.5 µm — paired * 7.1 µm — apical) % Table 7). Skeleton: Skeleton of both oscular rim and cormus tubes predominantly formed by triactines * tetractines rare % Fig. 17 C * D). In oscular tubes * spicules constitute organized array with their unpaired actines directed toward cormus and oriented more or less in parallel to proximo-distal axis of oscular tube % Fig. 17 C). In cormus tubes spicule array completely disordered % Fig. 17 D). Prominent oscular crown absent % Fig. 17 B). Both populations of diactines cover tubes’ surface * orienting in different directions and extending outside. Cytology: No material was available for cytological studies.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB8FFEAFEECFC7666E2F84A.taxon	distribution	Distribution: Arctic species. Molecular identity confirmed only for the White Sea and Greenland. Found subtidal up to 15 m on rocks and red algae.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB8FFEAFEECFC7666E2F84A.taxon	biology_ecology	Reproduction: No data about reproduction time for this species.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB8FFEAFEECFC7666E2F84A.taxon	discussion	Remarks: Although both our species’ delimitation analysis based on the H 3 dataset and morphological data suggest that this species represents a distinct species-level unit * we avoid describing a new species as this case requires additional studies for several reasons. Leucosolenia sp. A shares some features with Leucosolenia corallorrhiza: % i) the external appearance is similar * % ii) the angle between unpaired actines in tri- and tetractines is similar % the mean angle is 142.9 ° in L. corallorrhiza and 146.5 ° in Leucosolenia sp. A) * and % iii) the unpaired actines in tri- and tetractines are commonly shorter than the paired ones. However * these two species show several differences. Firstly * Leucosolenia sp. A has two populations of diactines * the smaller with lanceolate tips and the rare * large * curved * smooth * non-lanceolate diactines * whereas in L. corallorrhiza only the first type is present. Also * the tetractines are rare in both the cormus and oscular regions of Leucosolenia sp. A * while they are commonly present in the osculum of L. corallorrhiza. Leucosolenia sp. A commonly has triactines with bent * unpaired actines * which are straight in L. corallorrhiza. Finally * the mean length of actines in tri- and tetractines of L. corallorrhiza is shorter than those of Leucosolenia sp. A % L. corallorrhiza: 70.5 µm — unpaired actines mean length * 82.7 µm — paired actine mean length; Leucosolenia sp. A: 118.5 µm — unpaired mean length * 125.1 µm — paired mean length). At the same time * the limited material of Leucosolenia sp. A % only three specimens were collected and studied) does not allow us to study the possible interspecific variation and ontogenetic variation. Therefore * we avoid the designation of this species as a distinct one * until more material would be available for study.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB9FFECFC58FA2066C5FE67.taxon	description	(Figs 19 – 22; Table 8) ZooBank LSID: urn: lsid: zoobank. org: act: D 60461 BE-F 215 - 4 BE 2 - AFB 5 - 25 AF 542 FC 4 B 9.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB9FFECFC58FA2066C5FE67.taxon	materials_examined	Type material: Holotype: WS 11702 * White Sea * Kandalaksha Bay * Velikaya Salma Strait * vicinity of the N. A. Pertsov White Sea Biological Station * 0 – 2 m depth * 28. viii. 2018 * coll. A. I. Lavrov. Paratypes: WS 11703 * 1 specimen * White Sea * Kandalaksha Bay * Velikaya Salma Strait * vicinity of the N. A. Pertsov White Sea Biological Station * 0 – 2 m depth * 28. viii. 2018 * coll. A. I. Lavrov. WS 11728 paratype agrees in locality * date and collector with holotype WS 11702 and paratype WS 11703. WS 11655 was collected in 30. viii. 2017 * and WS 11725 * WS 11726 * WS 11771 were collected in 24. viii. 2018 * but all agree in locality and collector with holotype WS 11702 and paratype WS 11703. Type locality: White Sea * Kandalaksha Bay * Velikaya Salma Strait * vicinity of the N. A. Pertsov White Sea Biological Station % 66 ° 34 ʹN * 33 ° 08 ʹE). Material studied: Fifty-four specimens. Molecular data — 54 specimens * external morphology — 54 specimens * skeleton organization — three specimens % WS 11655 * WS 11728 * WS 11762) * spicules % SEM) — five specimens % WS 11579 * WS 11605 * WS 11704 * WS 11729 * WS 11775) * cytology % TEM) — three specimens % WS 11579 * WS 11600 * WS 11698) % Supporting Information * Table S 1).	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB9FFECFC58FA2066C5FE67.taxon	etymology	Etymology: From English ‘ creep’ * referring to specific decumbent cormus and unusual growth form of this species in contrast to sympatrically living Leucosolenia corallorrhiza.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB9FFECFC58FA2066C5FE67.taxon	description	External morphology: Length of cormus up to 5 cm. Cormus formed by basal reticulations of creepy tubes with one or several oscular tubes % Fig. 19 A). Tubes brittle. Oscular tubes creepy * trailing over substrate with slightly curved and erecteddistal end * sometimes with few diverticula. Oscular rim gradually narrows * possessing prominent spicular crown % Figure 19 A * B). Surface echinate. Coloration of living and preserved specimens greyish white % Fig. 19 A). Spicules: Diactines % Fig. 20 A * B). Spiny diactines * mean length 194.9 µm * mean width 5.1 µm % Table 8). Extremely variable in length * without lanceolate tips * spiny. Largest diactines slightly curved; intermediate and short diactines straight. Spines in distinct rows at one end of diactines * more or less reduced in large ones % Fig. 20 B). Triactines % Fig. 20 C * D). Sagittal * T-shaped and V-shaped % mean angle 131.1 °) % Table 8) * usually recurved * unpaired actines variable in length: most frequently shorter then paired actines * but equal and longer unpaired actines rarely occur % mean length: 80.7 µm — unpaired * 94.9 µm — paired) % Table 8). Aberrant T- and V-shaped triactines present * sometimes with undulated rays % Fig. 20 D). Unpaired actines often more slender than paired actines % mean width: 5.4 µm — unpaired * 5.9 µm — paired) % Table 8). Tetractines % Fig. 20 E). Quite rare. Sagittal * T-shaped and V-shaped % mean angle 139.5 °) % Table 8) * variable in size and proportions. Unpaired actines variable in length: longer * shorter * and equal to unpaired actines % mean length: 85.1 µm — unpaired * 95.3 µm — paired * 25.6 µm — apical) % Table 8). Paired and unpaired actines equal in width % mean width: 6.2 µm — unpaired * 6.3 µm — paired) % Table 8). Apical actine curved * smooth * and slender % mean width 5.2 µm) % Table 8). Skeleton: Skeleton of oscular rim predominantly formed by both tri- and tetractines * while in other body parts tetractines absent % Fig. 19 C * D). In oscular tubes * spicules constitute organized array with their unpaired actines directed toward cormus and oriented more or less in parallel to proximo-distal axis of oscular tube % Fig. 19 C). In cormus tubes * spicule array completely disordered % Fig. 19 D). Diactines form extending oscular crown up to 500 µm % Fig. 19 B) and cover tubes’ surface in large numbers * orienting in different directions and making it hispid. Cytology: Bodywall * 9 – 14 µmthick * threelayers: exopinacoderm * loose mesohyl * and choanoderm % Fig. 21 A * B; Supporting Information * Table S 2). Flat endopinacocytes located only in distal part of oscular tube % oscular ring) replacing choanocytes. Inhalant pores scattered throughout exopinacoderm * except the oscular ring area. Exopinacocytes non-flagellated T-shaped * rarely flat % Fig. 21 C). External surface covered by glycocalyx. Cell body % height 5.8 µm * width 2.8 µm) containing spherical to oval nucleus % diameter 2.7 µm) * submersed in mesohyl. Cytoplasm with specific * spherical * electron-dense inclusions % 0.25 – 0.35 µm diameter) % Fig. 21 C). Endopinacocytes non-flagellated * flat cells * size 16.2 µm × 2.7 µm % Fig. 21 D). External surface covered by glycocalyx. Nucleus % diameter 2.7 µm) spherical without nucleolus. Cytoplasm without specific inclusions % Fig. 21 D). Choanocytes flagellated trapeziform or prismatic % height 11.4 µm * width 3.6 µm) % Fig. 21 E). Flagellum surrounded by collar of microvilli. Characteristic pyriform nucleus % diameter 2.3 µm) in apical position. Cytoplasm with phagosomes and small vacuoles % Fig. 21 E). Porocytes tubular cylindrical % height 4.6 – 8.9 µm * width 2.8 – 2.9 µm) * connecting external milieu with choanocyte tube % Fig. 21 F). Nucleus oval to spherical % diameter 2.5 µm) * sometimes with nucleolus. Cytoplasm with spherical * electron-dense inclusions * identical with inclusions of exopinacocytes * phagosomes * and small vacuoles % Fig. 21 F). Sclerocytes amoeboid * size 7.6 µm × 2.9 µm % Fig. 22 A). Nucleus usually oval or pear-shaped % diameter 2.3 µm) * sometimes with single nucleolus. Well-developed Golgi apparatus and rough endoplasmic reticulum. Cytoplasm usually with phagosomes and / or lysosomes % Fig. 22 A). Amoebocytes of different shape % from oval to amoeboid) without special inclusions * size 5.7 µm × 2.6 µm % Fig. 22 B). Nucleus spherical % diameter 2.5 µm) * sometimes with nucleolus. Myocytes fusiform cells * size 16.5 µm × 3.3 µm * located in mesohyl. Nucleus oval % 2.4 µm × 1.9 µm) * without nucleolus % Fig. 21 D). Cytoplasm with mitochondria * ribosomes * small vesicles * and cytoplasmic myofilaments. Myofilaments grouped in bundles % diameter 0.25 – 0.32 µm) that are located along the long axis of the cell % Fig. 21 D). Two morphotypes of bacterial symbionts in mesohyl. Morphotype 1 numerous % Fig. 22 C * D). Bacteria large * rod-shaped * slightly curved * diameter 0.4 – 0.5 µm * length 2.7 µm. Cell is double * smooth * and covered with fibres * cytoplasm transparent with vacuolar inclusions * nucleoid region filamentous % Fig. 22 C * D). Morphotype 2 abundant % Fig. 22 E * F). Bacteria small * rodshaped * diameter 0.19 µm * length 1.9 – 2.1 µm. Cell wall smooth * cytoplasm transparent * nucleoid region filamentous % Fig. 22 E * F). Distribution: Arctic species. In the White Sea quite rare * found in low intertidal and upper subtidal zones up to 5 – 10 m depth * on kelps and rocks.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB9FFECFC58FA2066C5FE67.taxon	biology_ecology	Reproduction: In White Sea specimens * collected in mid-June to the end of the August contained oocytes at different stages % mostly * early) of development % Figs 21 B * 22 G).	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFB9FFECFC58FA2066C5FE67.taxon	discussion	Remarks: Leucosolenia creepae sp. nov. differs from other Leucosolenia species in both external characters and the morphology of spicules. In L. somesii * diactines are of two types: % i) smooth diactines * which are variable in length * and % ii) short and highly spined ones. In Leucosolenia creepae sp. nov. * we identified only one type of diactine * which has spines on the outer tip and variable in length. However * in Leucosolenia creepae sp. nov. * spines are more expressed in small and medium-sized diactines but become hardly visible in longer diactines of ~ 250 – 300 µm in length. In L. somesii * all medium-sized diactines have smooth tips % Fig. 24 B). Leucosolenia creepae sp. nov. forms a sparse * basal reticulation with few oscular tubes * while the cormus of L. somesii is formed by a dense reticulation of extremely branched * winding tubes. From all other North Atlantic and Arctic Leucosolenia species * Leucosolenia creepae sp. nov. differs by the absence of lanceolate diactines. The mesohyl cell composition of Leucosolenia creepae sp. nov. includes only amoebocytes * myocytes * and sclerocytes * which differs it from the sympatrically living L. corallorrhiza and L. variabilis % Supporting Information * Table S 2).	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFBFFFECFF45FE2264F8FBC0.taxon	description	(Figs 23, 24; Table 9)	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFBFFFECFF45FE2264F8FBC0.taxon	materials_examined	Type material: Lectotype BMNH 1925.11.2.24 * paralectotype BMNH 1925.11.2.25 * slides of the same: BMNH 1956.4. 26.35. Type locality: Brighton Aquarium. Material studied: One specimen * ZMA Por. 17572 % external morphology * skeleton organization * spicules) % Supporting Information * Table S 1).	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFBFFFECFF45FE2264F8FBC0.taxon	description	External morphology: Length up to 12 cm. Cormus formed by dense reticulation of extremely branched * winding tubes % Fig. 23 A). Surface hispid. Coloration of living and preserved specimens greyish white. Examined specimen lacks oscular tubes. According to the original description % Bowerbank * 1874) * sponges have numerous small and large oscular tubes * bearing a spicular crown. Oscular tubes erect and slightly curved * gradually narrowing to oscular rim. Spicules: Diactines % Fig. 24 A – C). Two populations of diactines: % i) curved * smooth diactines % Fig. 24 A * C) * mean length 424.5 µm * mean width 9.9 µm % Table 9) * slightly curved * smooth * variable in length * lacking lanceolate tips * with undulated tip and % ii) straight * spiny diactines % Fig. 24 B * C) * mean length 90.0 µm * mean width 3.3 µm % Table 9) * short * strait * lacking lanceolate tips * with numerous spines in distinct rows % Fig. 24 B). Triactines % Fig. 24 D * E). Sagittal * mostly T-shaped * but V-shaped also occur % mean angle 131.7 °) % Table 9) * unpaired actines usually shorter then paired actines * but longer * unpaired actines occur rarely % mean length: 127.4 µm — unpaired * 155.2 µm — paired) % Table 9). Paired and unpaired actines equal in width % mean width: 8.2 µm — unpaired * 8.0 µm — paired) % Table 9). Abnormal triactines common * sometimes with undulated rays % Fig. 24 E). Tetractines % Fig. 24 F). Quite rare. Sagittal * mostly T-shaped * but V-shaped also occur % mean angle 139.3 °) % Table 9) * unpaired actines usually shorter then paired actines * but longer * unpaired actines occur rarely % mean length: 156.0 µm — unpaired * 178.7 µm — paired * 21.5 µm — apical) % Table 9). Apical actines curved and smooth. All actines more or less equal in width % mean width: 9.1 µm — unpaired * 9.5 µm — paired * 10.0 µm — apical) % Table 9). Skeleton: Very dense net predominantly formed by triactines * oriented in different directions * tetractines rare % Fig. 23 B). Both trichoxea populations cover surface of tubes in large numbers * orienting in different directions and making it hispid. Skeleton of osculum was not studied.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFBFFFECFF45FE2264F8FBC0.taxon	distribution	Distribution: Boreal species. Described from Brighton Aquarium with confirmed reports from the Netherlands % van Soest et al. 2007). Probably it has wider distribution in the North-East Atlantic.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFBFFFECFF45FE2264F8FBC0.taxon	biology_ecology	Reproduction: No data on reproduction time are available.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
039D223DFFBFFFECFF45FE2264F8FBC0.taxon	discussion	Remarks: Leucosolenia somesii was considered a minor synonym of L. variabilis until a recent study by van Soest et al. % 2007) was published. They showed valuable differences between these two species * based on a large number of specimens * including the type material. Here we provide the first molecular data and an updated morphological description. Our novel data confirm that L. somesii represents a distinct species * based on both morphological and molecular analyses. The re-examination of spicules of specimen ZMA Por. 17572 studied by van Soest et al. % 2007) confirms the strong correspondence of its specular characteristics to the paralectotype BMNH 1956.4.26.35 % Fig. 23 C * D). According to our phylogenetic reconstruction * the most closely related species is Arctic Leucosolenia creepae sp. nov. * with which Leucosolenia somesii shares some specific morphological features: echinate external appearance due to the high number of non-lanceolate diactines protruding to the external surface * and dimensions of tri- and tetractines. The discussion of their differences is given above under the description for Leucosolenia creepae sp. nov .. From all other North Atlantic and Arctic Leucosolenia species * L. somesii differs by the absence of lanceolate diactines.	en	Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra, Ereskovsky, Alexander (2024): The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species. Zoological Journal of the Linnean Society 200: 876-914, DOI: 10.1093/zoolinnean/zlad104
