Schellencandona malardi, 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 : 115-122

Schellencandona malardi sp. nov.

urn:lsid:zoobank.org:act:

Figs 15–18 , 20 ; Tables 1 , 3

Diagnosis

Small trapezoid candonine of the genus Schellencandona (L = 485 µm). Carapace thick with strong ornamentation consisting of fossae on the entire valve surface. In lateral view, anterior margin widely rounded, while posterior margin poorly curved, dorsal margin straight or slightly concave in both valves, inclined backwards (decrease of 5.5% of H between the anterior and the posterior cardinal angle), postero-dorsal and ventral margins straight. Greatest H of LV located at the third anterior part (H/L = 0.49). In dorsal view, carapace swallen (W represents 50%–55% of L), pyriform and triangular shaped both anteriorly and posteriorly, with slightly beak-shaped ends. Calcified inner lamella amounting to c. 10% and 7% of L for the anterior and the posterior parts, respectively. A1 with a seta on the anterior side of the 3 rd podomere. Male A2: EII and EIII separated with t2 and t3 transformed in male bristles, 2 short z setae (z1 longer than z2), the longest claw (G2) represents 170% 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, poorly asymmetrical, both elongated and slightly curved. Walking leg (L6) with 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. Hemipenis with an outer lobe (a) large and sub-rectangular, dorso-distally oriented. The inner lobe (b) dorsally pointed (close to a 90° angle). Bursa copulatrix (e) rounded with a curved distal strip and an internal sub-conical structure. Female genital lobe rounded anteriorly without posterior expansion. Ocular structures not visible.

Etymology

The new species is named after Florian Malard who collected the species during an ecological study of the braided rivers of the southern French Alps.

Type material

Holotype

FRANCE • ♂, dissected appendages mounted in glycerine, valves stored in ethanol; Drôme district, Monjoux municipality; 44.5023° N, 5.0889° E; 446 m a.s.l.; Jun.–Jul. 2010; C. Capderrey leg.; interstitial habitat of the Lez River ; MNHN-IU-2023-714 .

Allotype

FRANCE • ♀; same data as for holotype; MNHN-IU-2023-715 .

Paratypes

FRANCE • 1 ♂; same data as for holotype; MNHN-IU-2023-716 ; MNHN • 1 ♂; same data as for holotype; UCBLZ. 2012-3-153-5 ; UCBLZ • 1 ♀; same data as for holotype; MNHN-IU-2023-717 ; MNHN • 1 juv.; same data as for holotype; UCBLZ. 2012-3-153-6 .

Other material examined

FRANCE • several juvs, undissected; same data as for holotype; UCBLZ. 2012-3-210 .

Description

MEASUREMENTS. Holotype, ♂ (MNHN-2023-714): LV: L = 485 µm, H = 240 µm (H/L = 0.49). RV=470 µm, H=230 µm (H/L=0.49). W=245 µm (W/L=0.50). Range for males (n=2): L=485 to 500 µm, H=240 to 245 µm, W=245 to 250 µm. Allotype, ♀ (MNHN-2023-715): LV: L=465 µm, H=240 µm (H/ L=0.51). RV: L= 455 µm, H=230 µm (H/L=0.50). W=255 µm (W/L=0.55). Range for females (n=2): L=465 to 490 µm, H=230 to 240 µm, W=255 to 260 µm.

CARAPACE. Whitish, with strong ornamentation (fossae) on entire carapace surface. General shape of carapace trapezoid with marked cardinal angles ( Figs 15 , 18I–J ). Highest H located at anterior third with H/L = 0.49 and 0.51 for male and female, respectively. Carapace viewed laterally with anterior margin widely rounded, posterior margin and ventral margin straight and dorsal margin inclined backwards (5.5% decrease of H between anterior and posterior cardinal angle). Carapace viewed dorsally ( Fig. 15C, F ) very enlarged, pyriform and triangular-shaped both anteriorly and posteriorly, with greatest W located at last third of animal (at 60% of L in both male and female), representing 50% and 55% of L for male and female, respectively. Anterior and posterior ends slightly beak-shaped.

VALVES. LV overlaps the RV on all sides ( Fig. 15A, G ). Dorsal margin of LV and RV slightly concave in the male. Dorsal margin representing 37% of LV length and 33% of RV length. Dorso-posterior margin straight on both valves. Ventral margin straight in LV and RV, slightly convex near oral area ( Fig. 15B, E ). Anterior calcified inner lamella larger (around 10% of L) than posterior one (7% of L for both sexes). Fused marginal valve zone narrow, representing 2.5% of L for both male and female, with straight and dense radial pore canals, more numerous anteriorly ( Fig. 15D ).

ANTENNULE, A1 ( Figs 16A , 17A ). I+II: A-1l(pu), P-2l(pu) / III: A-1s / 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, podomeres are in ratios of 1.8-1-1.5-1-1.5-1.6 from III to VIII. ya aesthetasc very long, 10.7 × as long as IV podomere.

ANTENNA, A2 ( Figs 16B–D , 17B–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 55% to 73% of EI length in male and female, respectively) and distally 2 setae (1s and 1m).

MALE A2 ( Fig. 16B–D ). EII and EIII segmented, 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 having length equal to 90% of that of EI. EIII with 1 short aesthetasc (y2), 2 external z setae, z1 slightly longer than EIV length, z2 short (15% of EI length). G1 reduced (96% of EI length), G2 well-developed (170% of EI length), G3 reduced to short bristle (45% of EI length). EIV with 2 claws, posteriorly 1 long (Gm, 165% of EI length) and anteriorly 1 reduced (GM, 69% of EI length), 1 small aesthetasc (y3, 39% of EI length) associated with subequal seta, g seta present.

FEMALE A2 ( Fig. 17B–D ). EII and EIII fused, with anteriorly 2 short aesthetacs (y1 and y2), 3 t setae, distally 2 z setae (both short). G2 claw reduced (85% of EI length). G1 and G3 claws well-developed and sub-equal (196% EI length). EIV with anteriorly 1 long (GM, 163% of EI length) and posteriorly 1 medium-sized claw (Gm, 129% of EI length), 1 medium-sized aesthetasc (y3, 79% of EI length) with subequal 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 16E , 17F ) 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, see detail in Fig. 16E ). 3 rd podomere with externally 3 setae, distally 1 long seta (γ) and internally 3 small setae. 4 th podomere with 2 serrated and long claws (160% of the 3 rd podomere length) and 3 small setae.

MAXILLULAR PALP (Mx1palp, Figs 16F , 17E ). 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 16I–J , 17G ). 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 weakly asymmetrical, both elongated and slightly curved; right one thicker than left one. Two endopodites bear 2 short but thick setae on ventral side and thin apical seta. In female, similar set of setae observed on protopodite (a, b, d). Exopodite plate with two filaments. Endopodite ending with three short setae.

WALKING LEG (L6, Figs 16G , 17J ). Five-segmented. Protopodite without d seta, EI without e seta, EII with f seta and EIII with 2 g setae. EIV with 2 short setae (h1 and h3) and long claw (h2) serrated and equal to 250% of length of EII.

CLEANING LEG (L7, Figs 16K , 17I ). Four-segmented (with EII and EIII fused). Protopodite with 1 short (d1) and 1 long setae (dp, 140% of EI length). EI without seta, EII+EIII with g seta (short in male and longer in female, 45% of EI length). EIV with 1 medium seta h1 (62 to 69% of EI length) and two long setae, h2 and h3 (118% and 195% of EI length, respectively).

CAUDAL RAMUS (CR, Figs 16M , 17H ). Slender, with relatively short sp seta (22%–25% of anterior margin of CR, not reaching basis of Gp), short sa seta and 2 relatively short and curved claws (Ga and Gp representing around 64–66% and 47–60% of anterior margin of CR, respectively), both claws serrated.

FEMALE GENITAL LOBE. Simple ( Fig. 17H ) widely rounded anteriorly without posterior expansion. Oocytes large (10% of valve length).

MALE GENITAL ORGANS. Zenker’s organ (male, Fig. 16L ) ith 6 internal rings of spines representing 23% of total length of carapace. Hemipenis ( Fig. 16H ) with distal outer lobe (a) dorso-distally oriented, large and sub-rectangular (with dorsal angle well marked in most individuals, but not all). Inner lobe (b) dorsally pointed, close to 90° angle, and small plication on ventral side. Lobe h not visible. Labyrinth well-sclerotized and divided in 4 sections, section d4 weakly reticulated. Copulatory tube thin located inside rounded bursa copulatrix (e) with well-sclerotized and curved distal strip and internal sub-conical structure. M-process flat with narrow and widely 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 malardi sp. nov. was sampled in the interstitial habitat of a single river, the Lez River, an east-side tributary of the Rhône River ( Fig. 1 , Table 1 ), at low elevation (i.e., 446 m a.s.l.). The species was exclusively sampled in groundwater upwelling zones (at the downstream end of gravel bars), never at a depth of 30 cm, rarely at a depth of 60 cm (10%) and mostly at a depth of 90 cm into the riverbed sediment (90% of the individuals). The water collected at a depth of 90 cm had a temperature ranging from 15.5 to 17.2°C, an electrical conductivity ranging from 407 to 452 µS. cm-1, a near-neutrality pH (7.4–7.7) and a wide range of dissolved oxygen concentration ( 2.15–7.3 mg ·L- 1).

Specialisation to groundwater: the well-developed aesthetascs (especially ya on A1 and Y on A2), the large size of the oocytes (10% of carapace length) and the lack of developed eyes suggest that Schellencandona malardi sp. nov. is specialized to groundwater life. Schellencandona malardi may thus be considered as a stygobiotic species endemic to the Lez River, living deep in the river bottom sediment and in a wide range of dissolved oxygen concentrations.

Taxonomic remarks

The new species fits with all the characteristics listed by Meisch (1996) for Schellencandona (see above) except for the surface of the carapace that is strongly ornamented with fossae on its entire surface. In the genus Schellencandona , the new species differs from all the species described in Europe and in Asia by the pyriform shape of the carapace in dorsal view. This shape is, for the moment, unique in the genus Schellencandona .

Schellencandona malardi sp. nov. has a hemipenis very similar to those of S. simililampadis and S. schellenbergi (stocky shape, with a large a lobe dorso-distally oriented, the h lobe not visible and a curved distal sclerotized strip on the bursa copulatrix), but differs from those of the above-mentioned species in (1) the presence of one seta in the 3 rd podomere of A1 (absent in the two other species) and (2) the size of the z2 seta on A2 not transformed in a claw and smaller than z1 (claw-like in the two other species).

To our knowledge, the most closely related species are two unpublished species of Schellencandona collected in the Jura Mountains (Northern French Alps, noted Schellencandona sp. J 1 and sp. J 3 in Dole-Olivier et al. 2009). These two undescribed species exhibit markedly different carapace shapes compared to those of Schellencandona malardi sp. nov., yet share a striking similarity in hemipenis shape as well as A1 and A2 chaetotaxy (for example, see A2 of Schellencandona sp. J 1 in Fig 19B ). At present, Schellencandona malardi can be regarded as related to this group of Jura Mountain species; however, this classification requires a thorough evaluation following the complete description of the group.

The similarity of Schellencandona malardi sp. nov. with the other species described here is detailed in the Discussion.

Figures

Fig. 15. Schellencandona malardi sp. nov. A–E. Holotype, ♂ (MNHN-IU-2023-714). A. Right view of the undissected specimen. B. Left valve, external view. C. Dorsal view of whole carapace. D. Detail of anterior margin. E. Right valve, external view. F–G. Allotype, ♀ (MNHN-IU-2023-715). F. Ventral view of whole carapace. G. Right view of the undissected specimen. Scale bars = 100 µm. Arrows point to anterior margin.

Fig. 16. Schellencandona malardi sp. nov., holotype, ♂ (MNHN-IU-2023-714). A. Antennule (A1). B. Antenna (A2). C. Detail of antenna, internal view. D. Detail of antenna, external view. E. Mandibular palp (Mdp). F. Maxillula (Mx1) palp. G. Walking leg (L6) with details of EIII and EIV. H. Hemipenis, inner view. I. Left 5th limb (with clasping organ). J. Right 5th limb (with clasping organ). K. Cleaning leg (L7). L. Zenker’s organ. M. Caudal ramus. Abbreviations: see Material and methods. Scale bars = 20 µm.

Fig. 17. Schellencandona malardi sp. nov., allotype, ♀ (MNHN-IU-2023-715). A. Antennule (A1). 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. Maxilla (L5). H. Caudal ramus with genital lobe. I. Cleaning leg (L7). 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).

Fig. 19. A. Schellencandona simililampadis (Danielopol, 1978), detail of male A2, external view (redrawn after Danielopol 1978). B. Schellencandona sp. J1 (UCBLZ 2012-3-14-36), detail of male A2, external view. Abbreviations: see Material and methods. Scale bars = 20 µm.