Echiniscus pusae Marcus, 1928

Gąsiorek, Piotr & Michalczyk, Łukasz, 2025, Novel integrative data for Indomalayan echiniscids (Heterotardigrada): new species and old problems, Organisms Diversity & Evolution 25 (1), pp. 81-116 : 93-103

publication ID	https://doi.org/10.1007/s13127-023-00628-5
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scientific name	Echiniscus pusae Marcus, 1928
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Species: Echiniscus pusae Marcus, 1928 View in CoL

Table 5, Figs. 7 View Fig and 8 View Fig

The dorsal plate sculpturing of E. pusae and E. africanus is almost identical; the main difference lies in the development of polygonal epicuticular edges of pores in paired segmental plates I–II: in E. africanus , these pores are poorly developed and only in the centroposterior plate portions are they comparable with those in the scapular and caudal plates ( Fig. 4 View Fig ), whereas in E. pusae , pores are developed in the entire posterior plate portions and well-developed, similarly to the scapular and caudal plates ( Figs. 7 View Fig , 8 View Fig ). However, despite some morphological similarities, E. pusae is not directly related to the africanus complex ( Gąsiorek et al., 2022), but was uncovered as sister to the virginicusperarmatus complex (Fig. 2). An evident epicuticular layer of ornamentation that overlaps with endocuticular layer of pillars and stiff spines in all trunk positions lend morphological support for such a grouping. One of the two main Echiniscus clades that comprises the africanus , blumicanadensis, granulatus-quadrispinosus, and virginicusperarmatus complexes can be characterised by a dominant dorsal plate sculpturing with large endocuticular pillars of polygonal shape and/or large epicuticular pores with polygonal edges. Among the taxa included in the analysis, only E. quadrispinosus Richters, 1902 diverges from this pattern, rendering its sculpturing as autapomorphic.

With reports from South and Central Africa ( Bochnak et al., 2020; Gąsiorek & Kristensen, 2018; Murray, 1907; Pilato et al., 2003), the Malay Archipelago ( locus typicus on Lombok, Marcus, 1928), and Australia ( Claxton, 2004), E. pusae is likely another species with a broad geographic distribution in the tropics.

Genus: Kristenseniscus Gąsiorek et al., 2019

There are three clear morphotypes within Kristenseniscus (as currently defined, see Discussion and the problem of diphyly of the genus): (i) pronounced epicuticular matrix in the form of granules and ridges, the latter dividing scapular, paired segmental, and caudal plates into well-demarcated subplates; rare micropores sometimes present ( K. tessellatus , Fig. 9A View Fig ); (ii) pronounced epicuticular matrix in the form of granules and ridges, the latter dividing only scapular and caudal plates into poorly-demarcated subplates; micropores absent ( K. limai , Fig. 9B View Fig ); (iii) epicuticular matrix reduced (with the exception of posterior portions of median plates and anterior margins + centroposterior portions of paired segmental plates), micropores in all plates (the K. walteri complex; Figs. 9C View Fig , 10 View Fig ). In the walteri complex, the false subdivision of dorsal plates into subplates may be limited to posterior portions of paired segmental plates ( Fig. 9C View Fig ); the endocuticular layer can be complex, exhibiting well-developed pillars arranged in multangular groups ( Fig. 9C View Fig , insert). Other species in the K. walteri complex have well-demarcated subplates, which may be regular ( Fig. 10A View Fig ) or with fuzzy margins ( Fig. 10B View Fig ).

Species: Kristenseniscus exanthema sp. nov.

Tables 6, 7 and 8, Figs. 11 View Fig , 12 View Fig and 13 View Fig

Locus typicus and type material: 3°23′53″S, 129°15′41″E, 109 m asl; Indonesia, the Moluccas, Seram , Tehoru ; moss and lichen from tree bark. Holotype (mature female on the slide ID.816.04), twelve paratypic females, seven juveniles and three larvae (slides ID.701.01–2, 4, 6, 8–10, ID.722.01–2, ID.816.03–4, 6–8, 10–12, ID.817.03). All are deposited in the Institute of Zoology and Biomedical Research of the Jagiellonian University in Kraków, Poland. GoogleMaps

Etymology: From Latin exanthema = rash. The name refers to the morphology of dorsum, calling to mind the human bumpy hives (urticaria). A noun standing in apposition.

Mature females (i.e. from the third instar onwards; measurements in Table 6). Body plump ( Figs. 11 View Fig , 12 View Fig ) and dark orange. Minute red eyes present. Primary and secondary clavae typical of the Echiniscus - type; peribuccal cirri with well-developed cirrophores. Cirrus A of moderate length (30–50% of the body length), with cirrophore; flagellum sometimes bifid ( Fig. 12A View Fig ).

Dorsal plates are strongly sclerotised and well-demarcated from each other, with greatly modified tessellatus type of sculpturing, in which epicuticular granules are restricted mainly to anterior and posterior margins of paired segmental plates ( Fig. 11 View Fig ), or otherwise may be absent ( Fig. 12B View Fig ). Instead, most of the surface of dorsal armour is sculptured with conspicuous micropores, and each micropore is surrounded with dark, usually multangular endocuticular matrix ( Figs. 11 View Fig , 12 View Fig ). The sculpturing vanishes in the anterior portions of median plate m2, anterior and lateralmost portions of paired segmental plates, the narrow patch anterior to the caudal (terminal) plate in the position of m3, and in a triangular zone of the caudal plate delimited by caudal incisions and lateral plate margins ( Figs. 11 View Fig , 12A View Fig ). The cephalic plate is uniform. The cervical (neck) plate is in the form of a narrow, rectangular belt, adjacent to the scapular plate; always unsculptured ( Figs. 11 View Fig , 12 View Fig ). The scapular plate is not divided into subplates, without incisions or sutures. Two median plates: m1 unipartite, whereas m2 bipartite. Two pairs of large segmental plates, their posterior portions are divided into three subplates by two weakly marked semicircular sutures ( Figs. 11 View Fig , 12A View Fig ). One pair of intersegmental lateral platelets embedded posteriorly to the scapular plate, and the second pair placed between paired segmental plates, both always unsculptured ( Fig. 11 View Fig ). The caudal (terminal) plate non-facetted and not divided into subplates, analogously to the scapular plate ( Figs. 11 View Fig , 12 View Fig ).

Ventral cuticle smooth; a hexapartite gonopore placed anteriorly to a trilobed anus, lying between legs IV. Sculptured pedal plates and pulvini are absent. Spine I is very thin ( Fig. 11 View Fig ). Dentate collar IV is composed of numerous short teeth. Papilla on leg IV is long ( Figs. 11 View Fig , 12A View Fig ). Claws IV are higher than claws I–III. External claws on all legs are smooth. Internal claws with needle-like spurs positioned at ca. 20% of the claw height, tightly adjacent to the branches and homomorphic on all claws; spurs may be asymmetrically missing on one claw ( Fig. 11A View Fig , inserts).

Juveniles (i.e. from the second instar onwards; measurements in Table 7). Clearly smaller than adult females. Qualitatively similar to adults, excluding the fact that epicuticular granules are more easily discernible ( Fig. 13 View Fig ). Gonopore absent.

Larvae (i.e. the first instar; measurements in Table 8). Clearly smaller than juveniles. No larger morphological disparities regarding older instars. Gonopore and anus absent.

Eggs. Up to two eggs per exuvia were found.

Phylogenetic position: Kristenseniscus exanthema sp. nov. is most closely related to Kristenseniscus cf. walteri 2 (Fig. 2 and SM.3).

Phenotypic differential diagnosis: Kristenseniscus exanthema sp. nov. is the only formally described member of Kristenseniscus that has uniform scapular and caudal plates, without subplates. Kristenseniscus cf. walteri 3 from Gunung Kinabalu (Borneo), not described in this work due to the lack of molecular data and the scarcity of individuals, shares this morphological state with K. exanthema sp. nov. but is easily distinguishable based on the endocuticular morphology resembling leopard spots under PCM ( Fig. 9C View Fig , insert).

Species: Kristenseniscus limai ( da Cunha & do Nascimento Ribeiro, 1964)

Amendments to the morphology of the species (based on the populations listed in Table 1 that correspond with the morphotype depicted by da Cunha and do Nascimento Ribeiro ): Anterior and posterior portions of paired segmental plates weakly demarcated ( Figs. 14 View Fig , 15A View Fig ). Three pairs of intersegmental lateral platelets: the first embedded micrometer) of selected morphological structures of juveniles of Kristenseniscus exanthema sp. nov. (type series)

mounted in Hoyer’s medium posteriorly to the scapular plate, the second placed between paired segmental plates, and the third embedded posteriorly to the second paired segmental plate ( Fig. 14 View Fig ). Subplates of the scapular plate developed only in its anterior half, with poorly developed epicuticular granules ( Figs. 14A, C View Fig , 15B View Fig ) or no granules ( Fig. 14B View Fig ). Each posterior portion of a paired segmental plate with a slightly semicircular, lateral epicuticular ridge formed by merged granules ( Figs. 14A–C View Fig ), not visible in juveniles ( Fig. 14D View Fig ). Caudal plate with four centrally positioned subplates and three epicuticular ridges: one at the posterior plate margin and two lateral ( Figs. 14A–C View Fig , 15C View Fig ). Only pedal plate IV was sculptured. Claws anisonych, as claws IV are on average slightly higher than claws I–III, with small and homomorphic spurs ( Fig. 14D View Fig , insert).

Species: Kristenseniscus tessellatus ( Murray, 1910)

Amendments to the morphology of the species (based on the populations listed in Table 1 that correspond with the morphotype depicted by Murray): Two pairs of intersegmental lateral platelets: the first embedded posteriorly to the scapular plate and the second placed between paired segmental plates ( Fig. 16A View Fig and fig. 1 in Dastych, 1997a). The pattern of subdivision of the scapular, paired segmental and caudal plates by epicuticular ridges into subplates is stable and well-identifiable due to the strong sclerotisation of the micrometer) of selected morphological structures of larvae of Kristenseniscus exanthema sp. nov. (type series)

mounted in Hoyer’s medium plates ( Figs. 16 View Fig and 17 View Fig ). Claws heteronych, as IV are higher than claws I–III, with heteromorphic spurs, which are positioned slightly higher on claw IV branches and more divergent from them than spurs on claw I–III branches ( Fig. 18 View Fig ).

Genus: Pseudechiniscus Thulin, 1911 (amended by Vecchi et al., 2016)

Subgenus: Meridioniscus Gąsiorek et al., 2023

Species: Pseudechiniscus (Meridioniscus) celebesiensis sp. nov.

Pseudechiniscus (M.) sp. 1 in Gąsiorek et al. (2021a)

Tables 9 and 10, Figs. 19 and 20

Locus typicus and type material: 1°44′59″S, 120°32′16″E, 701 m asl; Indonesia, Celebes, Sulawesi Tengah, Terjun Saluopa; moss from tree bark. Holotype (mature female on the slide ID.411.05), seven paratypic females, three juveniles and one larva (slides ID.411.01–7, mounted together with a female of Pseudechiniscus View in CoL (M.) angelusalas Roszkowska et al., 2020 and four females of P. (M.) quadrilobatus Iharos, 1969. All are deposited in the Institute of Zoology and Biomedical Research of the Jagiellonian University in Kraków, Poland.

Etymology: The name signifies terra typica. An adjective in the nominative singular.

Mature females (i.e. from the third instar onwards; measurements in Table 9). Body is small and slender (Fig. 19), orange. Minute black eyes are present in alive specimens, dissolving during mounting in Hoyer’s medium. Primary and secondary clavae elongated (dactyloid); peribuccal cirri with well-developed cirrophores. Cirrus A very short (<25% of the body length), with cirrophore.

Dorsal plates weakly sclerotised, but well-demarcated from each other, with the modified Pseudechiniscus type of sculpturing, in which typical endocuticular pillars form ornamented belts (Fig. 19A). The space between these belts of pillars is completely smooth. Pillars are unequal in size: the largest can be found in the scapular and caudal (terminal) plates, medium-sized—in the centromedian portions of the remaining plates, and the smallest—in the lateral portions of paired segmental and intersegmental plates. Pillars are randomly joined by minute striae visible under 1000 ×magnification in LCM. The cephalic plate is uniform, with a posterior incision. The cervical (neck) plate clearly delimited from both cephalic and scapular plates as a belt of pillars (Fig. 19A). The scapular plate divided into two parts by a central transverse suture. Two unipartite median plates m1–2. Two pairs of segmental plates, poorly divided into anterior and posterior portions. One pair of intersegmental lateral platelets embedded posteriorly to the scapular plate, and the second pair placed between paired segmental plates. The pseudosegmental plate IV’ merged indistinctly with the caudal plate on the lateral sides of the body, only in the median line there is a sclerotised border with a pair of robust teeth-like projections. Incisions absent in the caudal plate (Fig. 19A).

Ventral cuticle with a system of epicuticular thickenings (Figs. 19B, 20) that replaced the usual pattern composed of endocuticular pillars (the largest remaining accumulation of pillars is present in the subcephalic zone; Fig. 20 View Fig ). A hexapartite gonopore placed anteriorly to a trilobed anus that lies between legs IV. Pedal plates and pulvini are absent, instead patches of pillars are present centrally on each leg. Spine I and dentate collar IV are absent. Papilla on leg IV is present (Fig. 19B). Claws I–IV of equal heights, very slender and spurless (Fig. 19A, insert).

Juveniles (i.e. from the second instar onwards; measurements in Table 10). Clearly smaller than adult females. Qualitatively alike adults. Gonopore absent.

Larvae (i.e. the first instar; measurements in Table 10). Clearly smaller than juveniles. No larger morphological disparities regarding older instars. Gonopore and anus absent.

Eggs. Unknown.

Phylogenetic position: Pseudechiniscus (M.) celebesiensis sp. nov. is one of the most basal unveiled lineages within the subgenus Meridioniscus according to the analyses presented in Gąsiorek et al. (2021a) ( Pseudechiniscus (M.) sp. 1 therein).

Phenotypic differential diagnosis: There are two known Pseudechiniscus (Meridioniscus) species exhibiting teeth on the posterior margin of the pseudosegmental plate IV’ and spurless claws, but P. (M.) celebesiensis sp. nov. can be differentiated from:

• P. (M.) bidenticulatus, with locus typicus in Java ( Bartoš, 1963), by the distribution of endocuticular pillars in dorsal plates (arranged in ornamented belts in P. (M.) celebesiensis sp. nov. vs uniformly distributed in P. (M.) bidenticulatus), and by the teeth IV’ morphology (robust and prominent in P. (M.) celebesiensis sp. nov. vs minute and weakly developed in P. (M.) bidenticulatus);

• P. (M.) yunnanensis, described from tropical southern China ( Wang, 2009), by the distribution of endocuticular pillars in dorsal plates (arranged in ornamented belts and joined by tiny striae in P. (M.) celebesiensis sp. nov. vs uniformly distributed and joined by large striae in P. (M.) yunnanensis), and by the presence of median plate m3 (absent in P. (M.) celebesiensis sp. nov. vs present in P. (M.) yunnanensis).