Schellencandona mercantourensis, Issartel & Marmonier, 2025

Issartel, Colin & Marmonier, Pierre, 2025, Description of five new species of Schellencandona Meisch, 1996 (Ostracoda: Candoninae) from the southern French Alps, a highly diversified area for groundwater ostracods, European Journal of Taxonomy 1022, pp. 85-133 : 102-107

Schellencandona mercantourensis sp. nov.

urn:lsid:zoobank.org:act:

Figs 8–10 , 18 , 20 ; Tables 1 , 3

Synonymy

Candoninae sp. 3 – Dole-Olivier et al. 2015: 537, table 2.

Diagnosis

Small trapezoid candonine of the genus Schellencandona (L = 545 µm). Carapace thin without ornamentation. Anterior margin widely rounded, while posterior margin more pointed, dorsal margin straight in LV and slightly concave in RV, dorso-posterior margin slightly convex. Greatest H of LV located in the anterior third (H/L=0.50) in male. Strong asymmetry between the two valves: LV overlaps the RV, RV 4% shorter in length than LV, resulting in a posterior gap between the two valves. Anterior and posterior calcified inner lamellas amounting to c. 14% and 9% of L, respectively. A1 without seta on the 3 rd podomere and 2 setae on the 6 th podomere. Male A2: EII and EIII separated with t2 and t3 transformed in male bristles, 3 z setae (z2 longer than z1 and z3), the longest claw (G2) represents 175% of EI length. Female A2: EII+III with 3 t and 2 z setae (z1 longer than z2). 2 nd podomere of the Mdp bears 3+2 setae. Endopodites of the maxilla (L5) developed in males into prehensile palps strongly asymmetrical, the right one hook-shaped with a ventro-distal angle marked by a sclerotized hump. Walking leg (L6) with d, e, f setae and one g seta. Cleaning leg (L7) 4-segmented, EII and EIII fused, with 2 setae (d1 and dp) on the protopodite. Zenker’s organ with 6 internal rings of spines. The outer lobe (a) of the hemipenis large and rectangular shaped, dorso-distally oriented. The inner lobe (b) is dorsally widely rounded. Lobe h short and ventrally rounded. Bursa copulatrix (e) rounded with a conical internal structure and a well-sclerotized dorsal strip. Female genital lobe anteriorly slightly rounded with a small posterior triangular expansion. Ocular structures not visible.

Etymology

The new species is named after the Mercantour National Park where the species was collected during a groundwater biodiversity survey.

Type material

Holotype

FRANCE • ♂, dissected appendages mounted in glycerine, valves stored in ethanol; Alpes de Haute Provence district, Colmars les Alpes municipality; 44.1789° N, 6.6206° E; 1225 m a.s.l.; Sep. 2010; M.- J. Dole-Olivier leg.; interstitial habitat of the Verdon River ; MNHN-IU-2023-708 .

Allotype

FRANCE • ♀; same data as for holotype; MNHN-IU-2023-709 .

Paratype

FRANCE • 1 ♀, dissected appendages mounted in glycerine, valves stored in ethanol; Alpes Maritimes district, Saint Etienne de Tinée; 44.2344° N, 6.9492° E; 1080 m a.s.l.; Apr. 2009; M.-J. Dole-Olivier leg.; interstitial habitat of the Tinée River ; MNHN-IU-2023-710 .

Other material examined

FRANCE • 3 juvs, undissected; collected in the Verdon River; UCBLZ.2012-3-217.

Description

MEASUREMENTS. Holotype, ♂ (MNHN-2023-708): LV: L = 545 µm, H = 275 µm (H/L = 0.50). RV: L = 520 µm, H = 245 µm (H/L = 0.47). W = 190 µm (W/L = 0.34). Allotype, ♀ (MNHN-2023-709): LV: L = 510 µm, H = 275 µm (H/L = 0.54). RV: L = 485 µm, H = 250 µm (H/L = 0.52). W = 185 µm (W/L = 0.36). Paratype, ♀ (MNHN-2023-710): LV: L = 520 µm, H = 260 µm (H/L = 0.50). RV: L = 495 µm, H = 235 µm (H/L = 0.47). W = 170 µm (W/L = 0.33).

CARAPACE. Whitish and thin, without ornamentation. Carapace trapezoid with marked cardinal angles ( Figs 8 , 18E–F ). Highest H found at anterior third of animal (i.e., 42% of L). H/L = 0.50 for male and 0.50–0.54 for females. Carapace ( Fig. 8C, G ) moderately compressed in dorsal view, with greatest W at 50% of L, representing 0.33–0.36 of L. Anterior end weakly pointed. Posterior end moderately rounded.

VALVES. For both valves ( Fig. 8 ), anterior margin widely rounded, posterior margin more pointed, dorso-posterior margin slightly convex. Both valves are strongly asymmetrical: LV overlaps RV, RV 4% shorter in length than LV, causing posterior gap between two valves ( Fig. 8A, E ). Dorsal margin straight in LV and slightly concave in RV, representing 28% of L. Ventral margin straight in LV and slightly concave in RV for both male and female ( Fig. 8D, H ). Anterior calcified inner lamella larger (14% and 11% of L for male and female respectively) than posterior one (9% of L for both sex). Fused marginal valve zone narrow, representing 2.5% of L in both male and female, with straight and dense radial pore canals, more numerous anteriorly.

ANTENNULE, A1 ( Figs 9A , 10A ). I+II: A-1l(pu), P-2l(pu) / III: 0 /IV: A-1s/ V: A-1l, P-1s /VI: A-2l/ VII: A-2l-1s(α), P-1l/VIII: D-2l-ya-1l(cs). Using IV podomere as reference, lengths of podomeres are in the ratios of 1.2-1-1.1-1-1-1.1 from III to VIII in male. ya aesthetasc very long, equal to 6× as long as IV podomere.

ANTENNA, A2 ( Figs 9B–D , 10B–D ). Protopodite: coxa with 3 setae, 2 long and smooth, 1 short and plumose; basis with 1 long posterior seta; exopodite with 1 long and 2 short setae; EI with 1 posterior aesthetasc Y (equalling 69% of EI length) and distally 2 setae (1s and 1m).

MALE A2 ( Fig. 9B–D ). EII and EIII segmented forming 2 distinct podomeres. EII with 1 short aesthetasc (y1) and 4 t setae, t1 medium, t4 short, t2 and t3 transformed in male bristles with length equal to 94% of EI length. EIII with 1 short aesthetasc (y2), 3 external z setae, z1 and z3 slightly longer than EIV length, z2 of medium size (40% of EI length). G1 reduced (72% of EI length), G2 well-developed (175% of EI length), G3 reduced to long bristle (45% of EI length). EIV with 2 claws, posteriorly 1 long (Gm, 150% of EI length) and anteriorly 1 reduced (GM, 55% of EI length), 1 aesthetasc (y3, 58% of EI length) associated with subequal seta, g seta present.

FEMALE A2 ( Fig. 10B–D ). EII and EIII fused, with anteriorly 2 short aesthetacs (y1 and y2), 3 t setae, distally 2 z setae (z1 150% of EIV length and z2 short). G2 claw reduced (45% of EI length). G1 and G3 claws well-developed and sub-equal (185 and 160% of EI length, respectively). EIV with anteriorly 1 long (GM, 147% of EI length) and posteriorly 1 reduced claw (Gm, 50% of EI length), 1 long aesthetasc (y3, 70% of EI length) with sub equal seta, g seta present.

MANDIBLE. Consisting of coxal plate and 4-segmented palp (Mdp). Coxa typically shaped, heavily chitinized with masticatory part. 1 st podomere of Mdp ( Figs 9F , 10F ) with externally exopodite plate and 2 long setae, internally with 2 long setae (1 smooth and 1 plumose S1) and 2 short setae (1 smooth, α, and 1 plumose, S2). 2 nd podomere with externally 2 setae and internally group of 3 smooth setae and second group of 2 setae (1 long and 1 short, β). 3 rd podomere with externally 3 setae, distally 1 long smooth seta (γ) and internally 3 small setae. 4 th podomere with 2 serrated and long claws (2.2 × as long as 3 rd podomere) and 3 small setae.

MAXILLULAR PALP (Mx1palp, Figs 9E , 10E ). Two-segmented: 1 st segment with 4 apical plumose setae on outer corner. 2 nd segment with 2 claw-like setae (4.7 × as long as 2 nd segment) and 4 thinner setae.

MAXILLA (L5, Figs 9I–J , 10I ). With protopodite bearing 1 anterior seta (a) and 2 exterior setae (b and d), masticatory process (endite) apically with group of 10 setae. Exopodite plate with 2 filaments. Male endopodites transformed in clasping organs strongly asymmetrical. Right one strongly sclerotized, distal end hook-shaped, ventro-distal angle marked by sclerotized hump. Left one stocky and slightly curved. Two endopodites bear 2 short but thick setae on ventral side and thin apical seta. In female, similar set of setae observed on protopodite and 2 filaments on exopodite. Endopodite with 3 short apical setae.

WALKING LEG (L6, Figs 9G , 10J ). Five-segmented. Protopodite with one d seta, EI with one e seta (not observed in male holotype), EII with f seta and EIII with one g seta. EIV with 2 short setae (h1 and h3) and long claw (h2) serrated and equalling 145% the EI length.

CLEANING LEG (L7, Figs 9K , 10G ). Four-segmented (with EII and EIII fused). Protopodite with 1 short (d1) and 1 long setae (dp, 125% of EI length). EI without seta, EII+EIII with short seta (g). EIV with 3 long setae: h1, h2 and h3 (80%, 110% and 175% of EI length, respectively).

CAUDAL RAMUS (CR, Figs 9M , 10H ). Robust with medium-sized sp seta (22%–29% of anterior margin of CR, not reaching basis of Gp), short sa seta and 2 long and curved claws (Ga and Gp representing around 69–71% and 54–65% of the anterior margin of CR, respectively), both claws serrated.

FEMALE GENITAL LOBE ( Fig. 10H ). Anteriorly slightly rounded, with small posterior triangular expansion. Oocyte medium to large (9% of valve length).

MALE GENITAL ORGANS. Zenker’s organ ( Fig. 9L ) with 6 internal rings of spines representing 15% of total length of carapace. Hemipenis ( Fig. 9H ) with medium-sized distal outer lobe (a) and rectangular shaped, dorso-distally oriented. Inner lobe (b) dorsally widely rounded and small plication on ventral side. Lobe h short and ventrally rounded. Labyrinth well-sclerotized and divided in 4 sections, section d4 weakly reticulated. Copulatory tube thin located inside rounded bursa copulatrix (e) with marked dorsal sclerotized strip and conical internal structure. M-process flat with narrow rounded dorsal part, linked to C strip that joins base of e, and thin basal part reaching d4 section of labyrinth.

OCULAR STRUCTURES. Not visible.

Ecology and distribution

Schellencandona mercantourensis sp. nov. was sampled in the Mercantour National Park. It was collected in the interstitial habitat of two alpine rivers (i.e., the Verdon and Tinée rivers, Fig 1 ) at a depth of 50 cm into the riverbed sediment of two high-elevation sites (i.e., 1225 and 1080 m a.s.l., respectively). The species was not collected from the springs sampled in the same valleys and seems restricted to the interstitial habitat of the two rivers.

Specialisation to groundwater: the very long aesthetascs (ya on A1, Y and y3 on A2), the medium to large oocyte size (close to 9% of the body length) and the lack of a visible eye suggest a specialisation of the new species to groundwater. Schellencandona mercantourensis sp. nov. may be, for the moment, considered as a species specialized in riverbed sediment, with a narrow distribution area at high elevation in the Mercantour Mountains of the southern French Alps.

Taxonomic remarks

The general shape of Schellencandona mercantourensis sp. nov. is rather similar to the trapezoid S. schellenbergi and S. simililampadis , but the new species differs by its dorsal margin parallel to the ventral one (inclined backwards in the two other species), its convex dorso-posterior margin (straight in S. schellenbergi ), and the asymmetry of the two valves (see below).

The new species differs from the other European and Asiatic species by the following four characteristics: (1) the strong asymmetry between the two valves (RV 4% shorter in length than LV inducing a posterior gap between the two valves), (2) by the shape of the L5 clasping organs (especially the strongly sclerotized hook-shaped right one) and (3) the shape of the hemipenis, rather thin, with a distally oriented a lobe and a very small but visible distal rounded h lobe. These three characteristics have never been observed in the genus Schellencandona before.

Despite these differences, Schellencandona mercantourensis sp. nov. may be related to S. simililampadis because of two light similarities: (1) a rather similar A1 chaetotaxy, without seta on podomere III and the two setae on podomere VI, and (2) the A2 with a z2 seta very long compared to z1, but not transformed in a claw like in S. simililampadis and S. schellenbergi .

The comparison between Schellencandona mercantourensis sp. nov. and the other species described here is detailed in the Discussion.

Figures

Fig. 8. Schellencandona mercantourensis sp. nov. A–D. Holotype, ♂ (MNHN-IU-2023-708) A. Right view of the undissected specimen. B. Left valve, internal view. C. Dorsal view of whole carapace. D. Right valve internal view. E–H. Allotype, ♀ (MNHN-IU-2023-709). E. Right view of the undissected specimen. F. Left valve, external view. G. Dorsal view of whole carapace. H. Right valve, external view. Scale bars = 100 µm. Arrows point to anterior margin.

Fig. 9. Schellencandona mercantourensis sp. nov., holotype, ♂ (MNHN-IU-2023-708). A. Antennule (A1) with a detail of the 7th and 8th podomeres. B. Antenna (A2). C. Detail of antenna, internal view. D. Detail of antenna, external view. E. Maxillula (Mx1) palp. F. Mandibular palp (Mdp) with details of the 2nd podomere. G. Walking leg (L6). H. Hemipenis, outer view. I. Right 5th limb (with clasping organ) J. Left clasping organ. K. Cleaning leg (L7). L. Zenker’s organ. M. Caudal ramus. Abbreviations: see Material and methods. Scale bars = 20 µm.

Fig. 10. Schellencandona mercantourensis sp. nov., allotype, ♀ (MNHN-IU-2023-709). A. Antennule (A1). B. Antenna (A2). C. Detail of antenna, external view. D. Detail of antenna, internal view. E. Maxillula (Mx1) palp. F. Mandibular palp (Mdp) with details of the 2nd podomere. G. Cleaning leg (L7). H. Caudal ramus with genital lobe. I. Maxilla (L5). J. Walking leg (L6) with a detail of EIII and EIV. Abbreviations: see Material and methods. Scale bars = 20 µm.

Fig. 18. A–B. Schellencandona danielopoli sp. nov., holotype, ♂ (MNHN-IU-2023-701). A. Entire animal, right view. B. Dorsal view. C–D. Schellencandona capderreyae sp. nov., holotype, ♂ (MNHN-IU-2023-705). C. Entire animal, right view. D. Dorsal view. E–F. Schellencandona mercantourensis sp. nov., holotype, ♂ (MNHN-IU-2023-708). E. Entire animal, left view. F. Dorsal view. G–H. Schellencandona claretae sp. nov., holotype, ♀ (MNHN-IU-2023-711). G. Entire animal, right view. H. Dorsal view. I–J. Schellencandona malardi sp. nov. male (MNHN-IU-2023-714). I. Entire animal, right view. J. Dorsal view. Scale bars = 100 µm. Arrows point to anterior margin.

Fig. 20. Hemipenis (top) and L5 clasping organs (bottom) of the five new species of Schellencandona Meisch, 1996. Scale bars = 20 µm.

Fig. 1. Geographic distribution of the species of Schellencandona Meisch, 1996 in the southern French Alps. Solid lines = rivers; X = study sites without Schellencandona; dotted lines = western extension of Alpine glaciers during the Last Glacial Maximum (based on Julian 1997; Bosq et al. 2018).