Schellencandona claretae, 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 : 108-115

Schellencandona claretae sp. nov.

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Figs 11–14 , 18 , 20 ; Tables 1 , 3

Diagnosis

Small trapezoid candonine of the genus Schellencandona (L = ~545 µm for the female and ~480 µm for the male). Carapace thin with poor ornamentation consisting of pits and a few fossae in the centre of the valves. Anterior margin widely rounded, posterior margin more pointed, dorsal margin slightly concave in both valves, dorso-posterior margin straight. Greatest H of LV located in the anterior third (H/L = 0.48). Strong asymmetry between the two valves: LV overlaps the RV, RV 5% shorter in length than LV inducing a posterior gap between the two valves. Calcified inner lamella amounting to ca 13% and 12% of L for the anterior and the posterior ones, respectively. A1 without seta on the 3 rd podomere. Male A2: EII and EIII separated with t2 and t3 transformed in male bristles, 2 z setae (z2 medium to long), the longest claw (G2) represents 180% of EI length. Female A2: EII+III with 3 t and 2 z setae. 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 e, f and 2 g setae. 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) widely rounded posteriorly and the lobe h with a sub-triangular distal expansion. Bursa copulatrix (e) conical with a ventral well-sclerotized strip. Female genital lobe rounded without posterior expansion. Ocular structures not visible.

Etymology

The new species is named after Cécile Claret who collected the species during an ecological study of the Asse River.

Type material

The only available male has an unusual shape and length of its carapace. A female is therefore chosen as the holotype.

Holotype

FRANCE • ♀, dissected appendages mounted in glycerine, valves stored in ethanol; Hautes-Alpes district, Oraison municipality; 43.8793° N, 5.9051° E; 335 m a.s.l.; Jun. 2007; C. Claret leg.; interstitial habitat of the Asse River ; MNHN-IU-2023-711 .

Allotype

FRANCE • ♂; same data as for holotype; MNHN-IU-2023-712 .

Paratype

FRANCE • 1 ♀, dissected appendages mounted in glycerine, valves stored in ethanol; Alpes de Hautes 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-2023-713 .

Other material examined

FRANCE • 5 juvs, undissected; collected in the Asse River ; UCBLZ. 2012-3-168 ; UCBLZ • 1 juv., undissected; collected in the Verdon River ; UCBLZ. 2012-3-217 .

Description

MEASUREMENTS. Holotype, ♀ (MNHN-2023-711): LV: L = 545 µm. H = 265 µm (H/L = 0.48). RV L = 515 µm, H = 250 µm (H/L = 0.48). W = 210 µm (W/L = 0.38). Paratype, ♀ (MNHN-2022-713): LV: L = 545 µm, H = 270 µm (H/L = 0.49). RV: L = 525 µm, H = 235 µm (H/L = 0.45). W = 180 µm (W/L = 0.33). Allotype, ♂ (MNHN-2023-712): LV: L = 480 µm, H = 230 µm (H/L = 0.48). RV L = 450 µm, H = 215 µm (H/L = 0.47). W = 185 µm (W/L = 0.38).

CARAPACE. Whitish and thin, with poor ornamentation of rare pits and small fossae in centre of valves. General shape of carapace trapezoid with marked cardinal angles ( Figs 11A, E, G , 18G–H ). Highest H located at third anterior part of animal (i.e., at 39% of L) with H/L = 0.48 for both male and female. Carapace viewed dorsally ( Fig. 11D, F, H ) moderately compressed, with greatest W at 50% of L in female, representing 38% of L. Carapace of male with greatest W at last third, representing 38% of L. Anterior end weakly beak-shaped in both sexes. Posterior end moderately rounded in female ( Fig 11D ) and more pointed in male ( Fig. 11H ). In female collected in Verdon River, similar general shape of carapace in lateral view ( Fig. 11E; H /L = 0.49), but slenderer than holotype in dorsal view ( Fig. 11F ), with W representing 33% of L.

VALVES. Two valves strongly asymmetrical: LV overlaps RV, RV 5% shorter in length than LV inducing posterior gap between two valves ( Fig. 11A, E, G ). For both valves, anterior margin widely rounded, while posterior margin more pointed, dorso-posterior margin straight. Dorsal margin slightly concave, representing 34% of L. Ventral margin slightly convex in LV ( Fig. 11C, J ) and slightly concave in RV for both male and female ( Fig. 11B, I ). Anterior calcified inner lamella larger (13% and 14% of L for female and male respectively) than posterior one (12% of L for female and 10% for male). Fused marginal valve zone narrow, representing 2% of L for both male and female, with straight and dense radial pore canals, more numerous anteriorly. Strong difference between male and female, in size (12% difference, see below) and in shape of the carapace, especially in dorsal view. Greatest width at 50% of length in female and at last third in male. Posterior end gently rounded in female, pointed and triangular-shaped in male.

ANTENNULE, A1 ( Figs 12A , 13A , 14A ). 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, ratios of podomeres are 1.4-1-1.3-1.4-1.4-1.2 from III to VIII. ya aesthetasc very long, equalling 7.1× as long as IV podomere. Female of Verdon River with similar set of setae on A1 and similarly long ya ( Fig. 14A ). Using IV podomere as reference, ratios of podomeres are 1.6-1-1.3-1.2-1.5-1.6 from III to VIII.

ANTENNA, A2 ( Figs 12B–D , 13B–D , 14B–D ). Protopodite: coxa with 2 setae, only 1 long and smooth seta observed, and 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 68% of EI length) and distally 2 setae (1s and 1m).

MALE A2 ( Fig. 12B–D ). EII and EIII forming 2 distinct podomeres. EII with 1 short aesthetasc (y1) and 4 t setae, t1 and t4 short, t2 and t3 transformed in male bristles with length equal to 70% of EI length. EIII with 1 short aesthetasc (y2), 2 external z setae, z1 slightly shorter than EIV length, z2 of medium size (45% of EI length). G1 reduced (60% of EI length), G2 well-developed (180% of EI length), G3 reduced to short bristle (20% of EI length). EIV with 2 claws, 1 long posteriorly (Gm, 150% of EI length) and 1 reduced anteriorly (GM, 57% of EI length), 1 medium-sized aesthetasc (y3, 42% of EI length) associated with subequal seta, g seta not observed.

FEMALE A2 ( Fig. 13B–D ). EII and EIII fused, with anteriorly 2 short aesthetascs (y1 and y2), 3 t setae, distally 2 z setae (both short). G2 claw reduced (63% of EI length). G1 and G3 claws well-developed (205% and 180% of EI length, respectively). EIV with anteriorly 1 long (GM, 170% of EI length) and posteriorly 1 reduced claw (Gm, 80% of EI length), 1 long aesthetasc (y3, 83% of EI length) with subequal seta, g seta present. Female paratype of Verdon River ( Figs 14B–D ) with similar number of t and z setae on A2. Claws generally shorter than in the holotype: G2 reduced to 45% of EI length, G1 and G3 representing 190 and 175% of EI length. EIV with anteriorly 1 long claw (GM, 160% of EI length), posteriorly 1 reduced one (Gm, 50% of EI length) and y3 representing 57% of EI length, 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 13E , 14F ) with externally exopodite plate, internally with 2 long setae (1 smooth and 1 plumose S1) and 2 short setae (1 smooth α, 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 (166% of the 3 rd podomere length in holotype and 160% of 3 rd podomere in paratype from Verdon River) and 3 small setae.

MAXILLULAR PALP (Mx1palp, Figs 12E , 13F , 14E ). Two-segmented: 1 st segment with 4 apical plumose setae on outer corner. 2 nd segment with 2 claw-like setae (370% of 2 nd segment length) and 4 thinner setae.

MAXILLA (L5, Figs 12F , 13G ). With protopodite bearing 1 anterior seta (a) and 2 exterior setae (b and d), masticatory process (endite) apically with group of 11 setae. Exopodite plate with 2 filaments. Male endopodites ( Fig. 12F–G ) transformed in clasping organs markedly asymmetrical. Right one strongly sclerotized, distal end hook-shaped, ventro-distal angle marked by a sclerotized hump. Left one more rounded and slightly curved. Two endopodites bear 2 short but thick setae on ventral side and thin apical seta. In female ( Fig 13G ), similar set of setae observed on protopodite (a, b, d). Exopodite with 2 filaments and endopodite with 3 terminal setae.

WALKING LEG (L6, Figs 12I , 13I , 14G ). Five-segmented. Protopodite with d seta (not observed in the male), EI with e seta, EII with f seta and EIII with 2 g setae (only one observed in male). EIV with 2 short setae (h1 and h3) and long claw (h2) equalling 270% EII length. In paratype from Verdon River, similar setal arrangement observed (d, e, f and 2 g) with claw h2 representing 300% EII length.

CLEANING LEG (L7, Figs 12J , 13K , 14H ). Four-segmented (with EII and EIII fused). Protopodite with 1 short (d1) and 1 long seta (dp, 130–154% of EI length). EI without seta, EII+EIII with a short seta (g). EIV with 1 medium seta h1 (60–65% of EI length) and two long setae, h2 and h3 (130%–190% of EI length, respectively). In paratype from Verdon River, similar set of setae observed, with similar length for dp and h1, but slightly shorter h2 (120%) and h3 setae (160% of EI length).

CAUDAL RAMUS (CR, Figs 12L , 13H , 14I ). Robust, with long sp seta (33% of anterior margin of CR) exceeding basis of posterior claw, short sa seta, 2 long and curved claws (Ga and Gp representing around 90% and 79% of anterior margin of CR, respectively), both claws serrated. In paratype from Verdon River, sp shorter (representing 26% of CR, not reaching basis of Gp), and Ga and Gp also shorter compared to holotype from Asse River (representing 79% and 73% of CR, respectively).

FEMALE GENITAL LOBE. Simple ( Figs 13J , 14J ) simply rounded for both the holotype ( Fig. 13J ) and paratype ( Fig. 14J ), without posterior expansion. Oocytes large (14% of valve length).

MALE GENITAL ORGANS. Zenker’s organ ( Fig. 12K ) with 6 internal rings of spines representing 15% of total length of carapace. Hemipenis ( Fig. 12H ) with distal outer lobe (a) large and subrectangular, dorso-distally oriented. Inner lobe (b) widely rounded dorsally and with small plication on ventral side. Lobe h short with sub-triangular distal expansion. Labyrinth well-sclerotized and divided in 4 sections, section d4 weakly reticulated. Thin copulatory tube located inside conical bursa copulatrix (e) with well-sclerotized ventral strip C. The M-process flat with narrow rounded dorsal part, linked to C strip joining base of e and thin basal part reaching d4 section of labyrinth.

OCULAR STRUCTURES. Not visible.

Ecology and distribution

Schellencandona claretae sp. nov. was sampled in the interstitial habitat of two rivers located in the Southern Alps, both tributaries of the Durance River (the Verdon River and the Asse River, Fig 1 ). In the Verdon River, the species occurs at high elevation (i.e., 1225 m a.s.l.), at a depth of 50 cm into the riverbed sediment, but it has never been sampled in the springs of the same valley ( Dole-Olivier et al. 2015). In the Asse River, the species occurs close to the confluence with the Durance River ( Fig. 1 ), at low elevation ( 335 m a.s.l.). In the Asse River, the species always occurred deeper than 20 cm in the riverbed sediment: at a depth of - 80 cm in the main channel and at depths of -50 and - 80 cm in the ‘backwaters’ and the ‘phreatic ponds’ (partially or totally isolated secondary channels fed by groundwater, Table 2 ), respectively.

Specialisation to groundwater: the very long aesthetascs (ya on A1, Y, and y3 on A2), the large oocyte size (close to 10% of the body length), and the lack of eyes suggest specialisation of the new species to groundwater. Schellencandona claretae sp. nov. may be considered as a species living deep in river sediment, more frequently in marginal pools than in the main active channel, with a wide elevation range. The species is known only from two tributaries of the Durance River.

Morphological remarks

Variability between male and female

We observed strong differences between the male and the two females. The only male available for this species ( allotype (MNHN-IU-2023-712)) is a mature adult with complete development of the A2 (with male bristles), of the Zenker’s organ, the testes and the hemipenis, but with a surprisingly reduced size compared to the females of both the Asse and the Verdon rivers (12% shorter than the female). In addition, this male has a rather different shape in dorsal view, with a posterior end that is more pointed and triangular. It is not possible, for the moment, to be certain whether these differences between males and females are attributable to a sexual dimorphism characteristic of the species or are linked to a teratological development of the only available male (e.g., Rossetti & Martens 1996).

Variability between populations We observed some differences between the female collected in the Asse River (type locality; holotype (MNHN-IU-2023-711)) and the female collected in the Verdon River ( paratype (MNHN-IU-2023-713)). This latter appears slenderer in dorsal view (W/L = 0.33 vs 0.38) than the Asse River individual. It also has slightly smaller claws on A2 (i.e., G2 representing 45% vs 63%, Gm representing 50% vs 80% and ya representing 57% vs 83% of EI length, respectively) and shorter terminal setae on L7 (i.e., h2 representing 120% vs 130% and h3 representing 160% vs 190% of EI length, respectively) than the Asse River individual. Similarly, the caudal ramus of the female collected in the Verdon River is shorter and stockier than in the Asse River: Ga representing around 79% vs 90% of the anterior margin length, Gp 73% vs 79%, and Sp representing 26% vs 33%, respectively.

Taxonomic remarks

The general shape of Schellencandona claretae sp. nov. is rather similar to the trapezoid S. schellenbergi and S. simililampadis , but the new species differs by the strong asymmetry between the two valves (see below), its dorsal margin parallel to the ventral one (inclined backwards in the two other species), by its rounded anterior end in dorsal view (beak-shaped in S. schellenbergi ), and its pointed posterior margin (rounded in S. simililampadis ).

The new species differs from the other European and Asiatic species by the following characteristics: (1) strong asymmetry between the two valves (length of RV 5% shorter than LV with a posterior gap between the two valves), (2) the shape of the L5 clasping organs (especially the strongly sclerotized hook-shaped right one with a distal hump) and (3) the shape of the hemipenis, rather thin, with a distally oriented a lobe and a small triangular distal h lobe.

Despite these three differences, Schellencandona claretae sp. nov. may be related to S. simililampadis because of the following two characteristics: (1) a similar chaetotaxy of the A1, without seta on the podomere III in both male and female and two setae on the podomere VI and (2) the z2 seta of the A2 being very long compared to z1 (but not transformed in a claw like in S. simililampadis and S. schellenbergi ).

The similarity between Schellencandona claretae sp. nov. and the other species described here is detailed in the Discussion section.

Figures

Fig. 11. Schellencandona claretae sp. nov. A–D. Holotype, ♀ (MNHN-IU-2023-711). A. Right view of the undissected specimen. B. Right valve, internal view. C. Left valve, internal view. D. Dorsal view of whole carapace. E–F. Paratype, ♀ (MNHN-IU-2023-713). E. Right view of the undissected specimen. F. Dorsal view of whole carapace. G–J. Allotype, ♂ (MNHN-IU-2023-712). G. Right view of the undissected specimen. H. Dorsal view of whole carapace. I. Right valve, external view with details of pits and small fossae. J. Left valve, internal view. Scale bars = 100 µm. Arrows point to the anterior margin.

Fig. 12. Schellencandona claretae sp. nov., allotype, ♂, (MNHN-IU-2023-712), Asse River. A. Antennule (A1). B. Antenna (A2). C. Detail of antenna, internal view. D. Detail of antenna, external view. E. Maxillula (Mx1) palp. F. Left 5th limb (with clasping organ). G. Right clasping organ. H. Hemipenis, outer view. I. Walking leg (L6) with details of EIV. J. Cleaning leg, left clasping organ. K. Zenker’s organ. L. Caudal ramus. Abbreviations: see Material and methods. Scale bars = 20 µm.

Fig. 13. Schellencandona claretae sp. nov., holotype, ♀ (MNHN-IU-2023-711), Asse River. A. Antennule (A1). B. Antenna (A2). C. Detail of antenna, internal view. D. Detail of antenna, external view. E. Mandibular palp (Mdp) with details of the 2nd podomere. F. Maxillula (Mx1) palp. G. Maxilla (L5). H. Caudal ramus. I. Walking leg (L6) with details of EIII and EIV. J. Caudal ramus with genital lobe. K. Cleaning leg (L7). Abbreviations: see Material and methods. Scale bars: = 20 µm.

Fig. 14. Schellencandona claretae sp. nov., paratype, ♀ (MNHN-IU-2023-713), Verdon River. 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) G. Walking leg (L6) with details of EIII and EIV. H. Cleaning leg (L7). I. Caudal ramus. J. Caudal ramus with genital lobe. 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).