Schellencandona danielopoli, 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 : 90-96

Schellencandona danielopoli sp. nov.

urn:lsid:zoobank.org:act:

Figs 2–4 , 18 , 20 ; Tables 1 , 3

Diagnosis

Small candonine (L = 0.6 mm) of the genus Schellencandona with a triangular carapace covered with pits and small fossae. Greatest H of LV located just mid-length (H/L = 0.55). For both valves, anterodorsal margin slightly concave. Anterior margin widely rounded and posterior margin more acute. The two valves are strongly asymmetrical: LV with a dorsal hump that overlaps the RV, RV with a dorsal margin straight and slightly inclined backwards. A1 with a reduced number of setae: absence of seta on EIII and only one anterior seta on EVI. A2 with a penultimate segment subdivided in males with male bristles. Only 3 t setae (in female) and 3 z setae, z2 transformed in a claw in male. Mdp with 2+3 setae and γ setae smooth. L5 protopodite with two a setae; exopodite with 2 plates and endopodite transformed in a pair of clasping hook-like organs highly asymmetrical, right one stocky and poorly arched, left one slender and curved. L6 without d and e setae, but with one f and one g setae. L7 protopodite with 2 setae, EII and EIII fused bearing a g seta, EIV with two long (h2–h3) and one medium-sized (h1) setae. Female genital lobe rounded with a flat central part and without dorsal expansion. Zenker’s organ with 6 rings of spines. Hemipenis with outer lobe a large, rounded, dorso-distally oriented, inner lobe b sub-rectangular with a rounded ventral side. Bursa copulatrix (e) rounded with a curved sclerotized distal strip and an internal conical structure. M-process very flat. Ocular structures not visible.

Etymology

The new species is named after Dan L. Danielopol for his very important contribution to the systematics of ostracods.

Type material

Holotype

FRANCE • ♂, dissected appendages mounted in glycerine, valves stored in ethanol; Alpes-de-HauteProvence district, Montmaur municipality; 44.5608° N, 5.8952° E; 879 m a.s.l.; Jun.–Jul. 2010; C. Capderrey leg.; interstitial habitat of the main channel of the Buech River in a large braided sector ; MNHN-IU-2023-701 .

Allotype

FRANCE • ♀; same data as for holotype; MNHN-IU-2023-702 .

Paratypes

FRANCE • 1 ♂, dissected appendages and valves stored in ethanol; same data as for holotype; MNHNIU-2023-703 • 1 ♂; Drôme district, Verclause municipality; 44.3810° N, 5.4255° E; 534 m a.s.l.; Jun.– Jul. 2010; C. Capderrey leg.; interstitial habitat of the main channel of the Eygues River in a braided sector ; UCBLZ 2012-3-153-2 • 1 ♀; same data as for holotype; MNHN-IU-2023-704 • 1 juv.; same data as for the holotype; UCBLZ-2012-3-153-1 • 1 juv.; same locality as for holotype; undissected; UCBLZ-2012-3-207 .

Other material examined

FRANCE • 23 specs of diverse stages; Lez River at Montjoux ; UCBLZ-2012-3-207 • 1 juv.; Lez River at Grignan ; UCBLZ-2012-3-207 • 10 specs of diverse stages; Eygues River at Verclause ; UCBLZ-2012-3-207 • 2 juvs; Ouvèze River at Entrechaux ; UCBLZ-2012-3-207 • 2 juvs; Grand Buech River at Luce la Croix Haute; UCBLZ-2012-3-207 • 60 specs of diverse stages; Petit Buech River at Montmaur ; UCBLZ • 1 juv.; Buech River at Sisteron ; UCBLZ-2012-3-207 • 5 specs of diverse stages; Les Duyes River at Mallemoisson ; UCBLZ.2012.3.207 .

Description

MEASUREMENTS. Holotype, ♂ (MNHN-2023-701): LV: L = 600 µm, H = 330 µm (H/L = 0.55). RV = 588 µm, H = 290 µm (H/L = 0.49). W = 210 µm (W/L = 0.35). Range for males (n = 2): L = 575–600 µm, H = 570–588 µm, W = 210–225 µm. Allotype, ♀ (MNHN-2023-702): LV: L = 560 µm, H = 310 µm (H/L = 0.55). RV: L = 550 µm, H = 275 µm (H/L = 0.50). W = 205 µm (W/L = 0.36). Range for females (n = 2): L = 560–565 µm. H = 310–320 µm, W = 200205 µm.

CARAPACE. Whitish with ornamentation consisting of pits (or small fossae) in central part that vanish progressively toward periphery. General shape of carapace triangular ( Figs 2 , 18A–B ). Two valves strongly asymmetrical. LV overlaps RV with hump-like dorsal margin very variable ( Fig. 2A–B ) and without marked cardinal angles. Highest H located at middle of L. H slightly superior to ½ L: H/L= 0.55 for both male and female. Carapace viewed dorsally ( Fig. 2C, I ) moderately compressed, with greatest W at middle of L. Anterior and posterior ends weakly beak-shaped. Posterior end more pointed in female.

VALVES. For both valves ( Fig. 2 ), anterior margin widely rounded, while posterior margin more acute. Dorsal margin of LV hump-like and variable in males: H/L varying from 0.55 to 0.59 ( Fig. 2A–B ). Dorso-posterior margin straight or slightly concave in both sexes. Dorso-anterior margin slightly concave in both sexes. Ventral margin slightly convex in both males and females. RV is smaller than LV, trapezoidal with cardinal angles well marked, dorsal margin straight and slightly inclined backward, and ventral margin straight. Inner calcified lamella represents 11% of body length both anteriorly and posteriorly in males and slightly larger anteriorly than posteriorly in females. Fused marginal valve zone moderately large representing 2.5% of body length, with few and straight radial pore canals.

ANTENNULE, A1 ( Figs 3A , 4A ). I+II: A-1l(Pu), P-2l(Pu) / III:0 / IV: A-1s /V: A-1l, P-1s / VI: A-1l/ VII: A-2l-1s (α), P-1l /VIII: D-2l-ya-1l(cs). Posterior setae of I+II plumose. Using IV podomere as reference, ratios of podomeres in male 1-1-1.1-0.9-1.2-1.2 from III to VIII. ya aesthetasc long, 5–6.5 × as long as IV podomere.

ANTENNA, A2 ( Figs 3B–D , 4B–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 79% of EI length) and distally 2 setae (1s and 1l).

MALE A2 ( Fig. 3B–D ). EII and EIII segmented as two individuated podomeres; EII with 1 short aesthetasc (y1) and 4 t setae, t1 long and plumose, t4 short, t2 and t3 transformed in male bristles with length equal to 63% of EI length. EIII with 1 short aesthetasc and 3 external z setae, z1 and z3 shorter than EIV, z2 transformed in claw (170% of EI length), G1 reduced (65% of EI length), G2 well-developed (170% of EI length), G3 reduced to bristle (47% of EI length). EIV with 2 claws, posteriorly 1 long (Gm, 160% of EI length), anteriorly 1 reduced (GM, 90% of EI length), 1 aesthetasc (y3, 50% of EI length) associated with slightly shorter seta, g seta present.

FEMALE A2 ( Fig. 4B–D ). EII and EIII fused with anteriorly 2 short aesthetascs (y1 and y2), 3 untransformed t setae, distally 3 z setae (z1 and z2 of medium size, z3 short), reduced G2 claw representing 60% of EI length, and 2 well-developed claws G1 and G3 (both representing 170% of EI length). EIV with anteriorly 1 long (GM, 150% of EI length) and posteriorly 1 reduced claw (Gm, 75% of EI length), 1 aesthetasc y3 (58% of EI length) associated with a subequal seta, g seta present.

MANDIBLE. Consisting of coxal plate and 4-segmented palp (Mdp). Coxa typically shaped, heavily chitinized with a masticatory part. 1 st podomere of Mdp ( Fig. 3F ) with externally exopodite plate and 2 long setae, internally with 2 long setae (1 plumose S1) and 2 short setae (1 smooth, α, 1 plumose, S2). 2 nd podomere with externally 2 setae and internally a group of 3 smooth setae and a second group of 2 setae (1 long and plumose, 1 short, β). 3 rd podomere with externally 3 setae, distally 1 long and smooth seta (γ) and internally 3 setae (2 short setae and 1 longer). 4 th podomere with 2 serrated claws (170% of 3 rd podomere length) and 3 small setae.

MAXILLULAR PALP (Mx1palp, Fig. 3E ). Two-segmented. 1 st segment with 4 apical plumose setae on outer corner. 2 nd segment with 2 claw-like setae (4× as long as 2 nd segment) and 4 thinner setae.

MAXILLA (L5, Figs 3I–J , 4E ). With protopodite bearing 2 anterior a setae and 2 exterior setae (b and d), masticatory process (endite) apically with group of 10 setae. Exopodite plate with 2 plumose filaments. Male endopodites transformed in clasping hook-like organs with relatively high asymmetry, right one stocky and poorly arched, left one slender and curved, with 2 short but thick setae on ventral side and thin apical seta. In female, similar set of setae was observed on protopodite and 2 filaments on exopodite. Endopodite with 3 short apical setae.

WALKING LEG (L6, Figs 3G , 4H ). Five-segmented. Protopodite and EI without seta, EII with 1 f seta, EIII with 1 g seta, EIV with 2 short setae (h1 and h3) and long claw (h2) and equalling 160% of EI length.

CLEANING LEG (L7, Figs 3L , 4F ). Four-segmented (with EII and EIII fused). Protopodite with 1 short (d1) and 1 long (dp, 120% of EI length) setae. EI without seta, EII+EIII with short seta (g), EIV with 1 medium-sized seta (h1, 78% of EI length) and 2 long setae (h2, h3, 130 and 140% of EI length, respectively).

CAUDAL RAMUS (CR, Figs 3M , 4G ). Robust with a medium-sized to long sp seta (30% of anterior margin of CR) exceeding the basis of posterior claw, short sa seta and 2 long and curved claws (Ga and Gp). In males, these claws are rather short, representing respectively 72% and 66% of anterior margin of CR, but very long in females (i.e., 96% and 95% respectively), both claws serrated.

FEMALE GENITAL LOBE ( Fig. 4G ). rounded with flat central part and without dorsal expansion. Oocyte large (10.5% of valve length) and rounded.

MALE GENITAL ORGANS. Zenker’s organ ( Fig. 3K ) with 6 internal rings of spines representing 23% of total length of carapace. Hemipenis ( Fig. 3H ) with large rounded distal outer lobe (a) dorsally oriented, rectangular-shaped inner lobe (b) with straight distal end, rounded ventral angle and more pointed dorsal angle, with small plication on ventral side. Lobe h not observed. Labyrinth well-sclerotized and divided in 4 sections, section d4 weakly reticulated. Copulatory tube thin located inside rounded bursa copulatrix (e) with well-sclerotized distal strip and internal conical structure. M-process dorsally rounded, linked to C strip, and ventrally thin, joining d3 section of labyrinth.

OCULAR STRUCTURES. Not visible.

Ecology and distribution

Schellencandona danielopoli sp. nov. was collected from 8 sites of the braided river study ( Capderrey et al 2013): two sites along the Lez River, one site along each of the Eygues, Ouvèze, Buech and Les Duyes rivers. The first three rivers are left-side tributaries of the Rhône River, flowing at intermediate altitudes (i.e., between 207 and 534 m a.s.l.). The last two rivers flow at higher altitudes (i.e., between 466 and 1018 m a.s.l.) in the Durance catchment, in areas close to the margin of the Würm ice sheet ( Fig. 1 ).

In these 8 sites, the animals were mainly sampled in areas fed by groundwater upwellings (i.e., for 82% of the 102 individuals collected) with increasing abundances with depth into the river sediment (16% at - 30 cm, 21% at - 60 cm and 62% at - 90 cm). Schellencandona danielopoli sp. nov. was sampled in a wide range of temperature, from 11.1°C in the Petit Buech River at Montmaur to 19.9°C in the Buech River at Sisteron ( Fig. 1 , Table 1 ). It was collected at a depth of 90 cm into the bedsediment in interstitial water with a medium electrical conductivity (329–477 µS. cm-1), a pH ranging from 7.4 and 8.1 and a wide range of dissolved oxygen concentrations ( 3.2–7.1 mg ·L- 1).

Specialisation to groundwater: the length of ya of A1 and Y of A2 (i.e., more than 5 EIV podomere length of A1 and 79% of EI length of A2, respectively), the lack of eyes and the large size of the oocyte (10.5% of valve length) suggest that Schellencandona danielopoli sp. nov. is specialized for life in groundwater ( Danielopol 1973, 1980; Issartel & Marmonier 2025) as other species of Schellencandona , with a wide geographical distribution in the Southern French Alps, a wide altitudinal range and a marked ecological preference for deep river sediment layers.

Taxonomic remarks

The general shape of the carapace of Schellencandona danielopoli sp. nov. (triangular) is rather similar to the triangular S. triquetra and S. rhodanensis , but the carapace of the new species differs by its slightly concave dorso-anterior margin, while it is straight in the two other species, and its dorsal margin slightly inclined backwards, while it is parallel to the ventral margin in the two other species ( Figs 2 , 18A ).

In addition to the carapace shape, the soft parts of Schellencandona danielopoli sp. nov. differ from those of the other European species of the genus (i.e., S. triquetra , S. belgica , S. insueta , S. mira , S. rhodanensis ), but seems closely related to S. simililampadis and S. schellenbergi because of (1) the stocky shape of the hemipenis, with a large a lobe dorso-distally oriented, the h lobe not visible and the curved distal sclerotized strip on the bursa copulatrix, (2) the A2 with a z2 seta transformed in a claw in males (see Fig. 19A for A2 of S. simililampadis ) and (3) the reduced number of setae on the A1, especially the lack of seta on the podomere III in both males and females (but a seta is present in S. schellenbergi ). In contrast, Schellencandona danielopoli differs from S. simililampadis and S. schellenbergi in the following four characteristics: (1) triangular shape of the carapace (trapezoid in the two other species), (2) single anterior seta on podomere VI of A1 (two setae in the others), (3) two a setae on L5 (one in the others), and (4) lack of d and e setae on L6 (present in S. simililampadis ).

The different populations of Schellencandona danielopoli sp. nov. do not show any significant inter-population variability in both the carapace shape (because of a high intra-population variability of the dorsal margin, see Fig. 2A–B ) and in the soft-part morphology (similar chaetotaxy in males from the Buech River ( holotype, ♂ (MNHN-IU-2023-701)), and from the Eygues River ( paratype, ♂ (UCBLZ 2012-3-153-2)).

Finally, the similarity of Schellencandona danielopoli sp. nov. with the other species described here is detailed in the Discussion.

Figures

Fig. 2. Schellencandona danielopoli sp. nov. A, C–D, E–F. Holotype, ♂ (MNHN-IU-2023-701), right view of the undissected specimen. A. Right view of an undissected male. B. Paratype, ♂ (MNHN- IU-2023-703), detail of dorsal margin. C. Dorsal view of whole carapace. D. Left valve, external view. E. Detail of anterior margin. F. Right valve, external view. G–J. Allotype, ♀ (MNHN-IU-2023-702). G. Right view of undissected female. H. Left valve, internal view. I. Dorsal view of whole carapace. J. Right valve, internal view. Scale bars = 100 µm. Arrows point to anterior margin.

Fig. 3. Schellencandona danielopoli sp. nov., holotype, ♂ (MNHN-IU-2023-701). 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). G. Walking leg (L6). H. Hemipenis, medial view. I. Right clasping organ.J. Left 5th limb (with clasping organ). K. Zenker’s organ. L. Cleaning leg (L7). M. Caudal ramus. Abbreviations: see Material and methods. Scale bars = 20 µm.

Fig. 4. Schellencandona danielopoli sp. nov., allotype, ♀ (MNHN-IU-2023-702). A. Antennule (A1). B. Antenna (A2). C. Detail of antenna, external view. D. Detail of antenna, internal view. E. Maxilla (L5). F. Cleaning leg (L7). G. Caudal ramus with genital lobe. H. Walking leg (L6). 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.