Scleroconcha tuberculata, Chavtur, Vladimir G. & Keyser, Dietmar, 2016

Chavtur, Vladimir G. & Keyser, Dietmar, 2016, Benthic myodocopid Ostracoda (Philomedidae) from the Southern Ocean, Zootaxa 4141 (1), pp. 1-70 : 6-20

Scleroconcha tuberculata sp. nov. Chavtur

( Figs. 2–11 )

Etymology. The specific name “ tuberculata ”, from the Latin “tuberculum” [engl.: small hump], refers to sclerotic tubercles on the medial eye.

Holotype. MIMB 18268—adult male, (length 4.20 mm), appendages mounted on slide and valves in ethanol (70%).

Type-locality. D/E “Ob “, 8th Soviet (Russian) Antarctic Expedition, 19. February 1963, station E, sample 2, lat. 67°40’1”S, long. 45°48’5” E, depth—unknown, sandy bottom.

Paratypes (coordinates, depth and bottom sediment see Appendix). D/E “Ob“, 8th Soviet (Russian) Antarctic Expedition, station E, sample 2: MIMB 18269—adult female (length 4.50 mm), MIMB 18270—adult female (4.45 mm), MIMB 18271—adult female (carapace deformed), MIMB 18272—adult female (4.32 mm), MIMB 18 273— immature male (3.12 mm), MIMB 18275a, b, c—adult females (4.50, 4.41 and 4.34 mm).

R /V “Academic Fedorov”, 34th Soviet (Russian) Antarctic Expedition, station 16/62, sample 2: MIMB 18274—immature male A-1 (4.04 mm).

RV “Polarstern”, ANT VIII/5, station 16-477: ZMH-K-42259—immature male A-1 (3.42 mm).

RV “Polarstern”, ANT XIII/3, station 39/05/EBS: ZMH-K-42260—immature male (3.15 mm) and ZMH-K- 42261—immature female A-1 (3.46 mm).

RV “Polarstern”, ANT XV/3, station 114: ZMH-K-42262—immature female (3.62 mm).

Additional material. See Appendix.

Diagnosis of adult female. Carapace: Length 4.32–4.53 mm. Carapace reticulate with ribs along ventral and dorsal margins, one rib lying just within antero-ventral valve margin and being present only on anterior half of valve; middle rib extending full length of valve and lying dorsal of the central muscle attachments; a lower rib extends almost full length of valve and lies below the central muscle attachments. Surface of valves with scattered undivided setae.

Seventh limb. Each limb with 10–12 setae, 6 in distal group and 4–6 in proximal group. Terminal limb with 13– 17 pegs in total (on comb and opposite comb); teeth on comb absent.

Caudal furca. Each lamella with 15–17 claws; 3rd claw slender and slightly longer than 4th claw.

Bellonci organ. Organ elongate with about 22–28 segments at proximal part (including base) and middle.

Medial eye. Large, with 3 sclerotic tubercles, 1 dorsal, 1 anterior and 1 lateral.

Diagnosis of adult male. Carapace. Length 4.20 mm.

Seventh limb. Each limb with 8–9 setae, 4 in distal group and 4 or 5 in proximal group; terminal comb with 1 bare peg and 3 pegs present on opposite comb.

Caudal furca. Each lamella with 13 claws; 3rd claw slender and slightly shorter than 4th claw.

Bellonci organ. Organ elongate with about 32 segments at proximal (including base) and middle part.

Medial eye. Large, with 3 sclerotic tubercles, 1 dorsal, 1 anterior and 1 lateral.

Description of adult female. Carapace ( Figs. 3 A–E; Plate 1 ). Length 4.32–4.53 mm. Its shape, number and position of ribs and ornamentation identical to S. appelloefi ( Skogsberg 1920: 419–420, Fig. LXXVII) and S. gallardoi ( Kornicker 1971: 194; 1975: 322, Figs. 197, 202). Middle rib lying below central muscle attachments extending almost full length of valve and straight into anterior half. Rostrum with powerful ventral process and rounded distally ( Fig. 3 B). Incisure broad and almost rectangular. Infold on rostrum unstudied (this part of carapace of all specimens was covered by sedimentary crystals. Antero-ventral inside with 11–12 striations and about 8 minute setae ( Fig. 3 D). Surface of valves with scattered undivided setae ( Fig. 3 E).

First antenna. First joint bare; second joint with 1 dorsal and 1 ventral long setae and 1 lateral relatively short seta, barely reaching fifth joint, all setae spinous; third joint with 3 setae, 1 ventral and 2 dorsal; fourth joint with 4 ventral and 2 dorsal setae; sensory seta of fifth joint with 6 proximal and 5 terminal filaments; sixth joint with long, spinous medial seta; seventh joint: a-seta spinous, somewhat longer than seta on sixth joint; b-seta with 4–5 proximal and 5 terminal filaments; c-seta with 7 proximal and 5 terminal filaments; d- and e-setae bare, subequal, longer than a-seta; f-seta with 2 proximal and 4 terminal filaments; g-seta with 6 proximal and 5 terminal filaments. Joints 2 to 5 with short spines forming clusters along ventral and dorsal margins.

Second antenna ( Fig. 3 J,K). Exopodite: first joint with minute elongate process on distal margin; distal margin joints 2–8 with spines in row and with minute basal spines; ninth joint with 7 setae consisting of 4 long and 3 short setae. Endopodite 2-jointed: first joint with 5 proximal and 1 distal setae, proximal seta in proximal group longer than others; second joint with extremely long, spinous ventral seta reaching terminal margin of exopodite, short bare seta and minute process on terminale of this joint.

Mandible ( Fig. 5 ). Coxale: endite spinous with minute seta at its base and bifurcate tip. Basale: dorsal margin with 1 long bare seta anterior to middle and 2 subterminal setae of which 1 spinous and other bare; medial side with 6 setae, 1 near middle with long proximal spines and 5 proximal (3 pectinate and 2 spinous); lateral surface with 4– 5 setae forming a row parallel to ventral margin; ventral margin with 4 distal setae. Exopodite about 3/4–4/5 length of first endopodial joint and with pointed or rounded tip and 2 long, spinous subterminal setae. Endopodite: ventral margin of first joint with 4 spinous setae; dorsal margin of second joint with 4 or 5 setae in proximal group and 6 (or rarely 7) in distal group, ventral margin of its joint with 3 setae in subterminal group and 3 setae in terminal group, proximal surface of this joint covered with short spines forming clusters; end joint with 3 claws and 4 setae.

Maxilla: Endite I with 10 spinous and pectinate setae, endite II with 6 spinous and pectinate setae, endite III with 9 spinous and pectinate setae; first endite broader than second and third endites, third endite longer than first and second endites. Endopodite: first joint with 1 α-seta and 5 β-setae; second joint with 3 a-setae (normal type), 2 b-setae (of which 1 claw and other normal), 3 c-setae (normal type) and 2 d-setae (claws).

Fifth limb ( Fig. 6 A). Epipodite appendage with about 56–61 plumose setae. Exopodite: inner margin of large tooth of second joint with rounded or small pointed tooth. Fourth plus fifth joints total with about 7 setae.

Sixth limb. Endite I with 2 terminal and 1 medial setae; endite II with 3 (rarely 4) terminal and 1 medial setae; endite III with 7–8 terminal and 1 medial setae; endite IV with 7–8 terminal and 1 medial setae; end joint with 31– 35 setae; 3–4 setae present in place of epipodial appendage; medial and lateral surface of end joint with abundant long setules. Shape of limb similar to that figured by Skogsberg (1920: 425, Fig. LXXXI).

Seventh limb ( Fig. 6 B–G). Each limb with 10–12 setae, 6 (3+3) in distal group and 4–6 (3+3, 3+2 and 2+2) in proximal group; each distal seta with 3–7 bells and each proximal seta with 4–5 bells; terminally, limb with 13–17 pegs (total on comb and opposite comb; teeth on comb absent!).

Caudal furca ( Fig. 6 H). Each lamella with 15–17 claws. 3rd claw more slender and slightly longer than 4th claw; claws 5 to 15–17 decreasing in length posteriorly along lamella.

Bellonci organ ( Figs. 3 F–I; 4 A–C). Organ elongate with about 22–28 segments at proximal part (including base) and middle; tip usually pointed or rarely blunt.

Lateral eye ( Fig. 4 I). Eye elongate with 2 undivided ommatidia.

Medial eye ( Fig. 4 A–G). Large, with 3 sclerotic tubercles, 1 dorsal, 1 anterior and 1 lateral.

Upper lip ( Fig. 4 A, B, H). Lip hirsute ventrally and with several glandular processes at tip; large rounded process present between upper lip and base of first antenna.

Description of adult male. Carapace ( Fig. 7 A–G). Length 4.20 mm. Carapace more elongate than in female, shell thin, flexible, smooth with 3 longitudinal ridges barely perceptible; caudal process similar in shape to that on female valve; incisure more open than that on female; rostrum without lateral flap. Rostral infold with about 8–9 setae in a row. Surface of valves with scattered undivided setae ( Fig. 7 G, plate 1 E).

First antenna. First joint bare, second, third and fourth joints with spines forming clusters on medial and lateral surface; second joint with 3 spinous setae, 1 dorsal, 1 ventral and 1 lateral; third joint with 1 ventral and 2 dorsal setae; fourth joint short with 2 dorsal and 4 ventral (3 thick and long and 1 thin and short) setae; fifth joint triangular, inserted ventrally between fourth and sixth joint; sensory seta with abundant long filaments on broadened proximal part and 5 short distal filaments including tip; sixth joint with disto-medial seta with long spines at middle and short distal marginal spines. Seventh joint: a-seta about same length as seta of sixth joint; bseta stout with 3 proximal and 4 distal filaments; c-seta extremely long with 13 long filaments. Eight joint: d- and e-setae bare, subequal, somewhat longer than seta of sixth joint; f-seta about same length as c-seta and with 14 filaments; g-seta with 5 proximal and 4 distal filaments.

Second antenna ( Fig. 8 A–F). Exopodite: second joint bare; joints 3 to 8 with 2–4 minute basal spines ( Fig. 8 A); ninth joint with 6 setae. Endopodite: first joint with 5 proximal and 1 distal setae ( Fig. 8 C), second joint elongate with 3 setae near middle of ventral margin, and 1 thin and short subterminal seta; third joint elongate, reflexed, with 9–10 teeth along inner margin ( Fig. 8 C–E), 2 short subterminal setae; and terminal ridges (barely visible).

Mandible ( Figs. 8 G–I; 9 A–D). Coxale endite represented by 2 distinct spines ( Fig. 8 I). Basale: medial surface with 7 setae (5 proximal and 2 distal) on left limb and 5 setae (4 proximal and 1 distal) on right limb; ventral margin with 6 setae on left limb and 8 setae on right limb (some of these with bases on lateral side); dorsal margin with 1 long bare seta distal to middle and 2 long spinous subterminal setae; medial surface of joint with clusters of spines. Exopodite on right limb reaching past middle of dorsal margin of first endopodite joint, with 2 long terminal setae (of which one spinous and other bare); on left limb exopodite aberrant and represented by a short tubercle with 1 relatively long bare seta ( Figs. 8 G, 9 A). Endopodite on right limb: first joint with 3 long and 1 short ventral setae; second joint with 7 dorsal setae (1 proximal and 6 grouped near the middle) and 2 distal groups of setae, each with 3 setae; medial surface and ventral margin of joint with spines forming clusters; end joint with 3 claws and 4 setae, of which 2 very short, 1 of medium length and 1 long. Endopodite of left limb abnormal: first joint with 3 ventral setae; second joint with 7 dorsal, 2 lateral and 4 ventral setae; medial surface and ventral margin with spines forming clusters; end joint with 3 claws and 4 setae, 1 short and 3 long; first and second joint somewhat shorter than that on right limb. All setae, as well as short and medium long claws on endopodite bare, while main claw with faint teeth.

Maxilla and Fifth limb deformed.

Sixth limb. Endites I to III deformed; endite IV with 9 setae; end joint with 29 setae; 2 setae present on place of epipodial appendage.

Seventh limb ( Fig. 9 E). Each limb with 8–9 setae, 4 in distal group (2+2) and 4 or 5 in proximal group (2+2 or 2+3); each distal seta with 3–7 bells and proximal seta with 2–4 bells; terminal comb with 1 bare peg (teeth on comb absent) and 4 bare pegs present on opposite comb.

Caudal furca ( Fig. 9 F). Each lamella with 13 claws. 3rd claw slender and slightly shorter than 4th claw; claws 5 to 13 decreasing in length posteriorly along lamella.

Copulatory appendage. Organ extremely small, inconspicuous.

Bellonci organ ( Fig. 7 H, I). Organ elongate, with about 32 segments at proximal part (including base) and middle, and with pointed tip.

Lateral eye ( Fig. 9 G). Each eye with about 48 divided ommatidia; eyes large and pigmented.

Medial eye ( Fig. 7 H, J). Large, with 3 sclerotized tubercles, 1 dorsal, 1 anterior and 1 lateral. Upper lip and anterior process of body between lip and base of first antenna similar to that of female ( Fig. 7 H).

Description of A- 1 male. Carapace ( Figs. 10 A–F; 11 C–E). Shape of carapace similar to that of adult female, but more elongate and truncate posteriorly. Length 3.15–4.04 mm. Infold of rostrum with 6–9 setae forming a vertical row.

First antenna ( Fig. 11 F). Second joint with 3 setae, 1 dorsal, 1 ventral and 1 lateral.

Second antenna ( Figs. 10 J, K; 11 G–J). Endopodite: first joint with 4 or 5 proximal and 1 distal setae; second joint with long spinous proximal setae (somewhat longer than endopodite) and 2 short bare setae near middle on ventral margin; third joint with midlength dorso-proximal setae and 2 short (3 as exception) subterminal setae.

Mandible. Coxale, exopodite and first joint of endopodite similar to that of adult female. Ventral margin of basale only with 3 distal setae. Dorsal margin of second endopodial joint with 2 setae in proximal group, 1 middle seta and 7 setae in distal group; ventral margin with 2 setae in subterminal group and 3 setae in terminal group.

Sixth limb. Endite I with 3 setae, endite II with 4 setae, endite III with 8–10 setae, endite IV with 8–9 setae, end joint with 23–26 setae; 3 setae present in place of epipodial appendage.

Seventh limb ( Fig. 10 L). Limb similar to that of adult female.

Caudal furca. Each lamella with 14 or 15 claws. 3rd claw slender and somewhat longer than 4th claw; claws 5 to 14–15 decreasing in length posterior along lamella.

Bellonci organ ( Fig. 10 I; 11 F). Organ elongate, with 11–19 segments at proximal part (including base) and middle, and pointed or rounded tip.

Medial eye, upper lip and anterior process of body ( Figs. 10 I; 11 F). Similar to that of adult female.

Description of A- 1 female. Carapace ( Figs. 10 G, H; 11 A, B). Shape of carapace similar to that of adult female or elongate as in A- 1 male. Length 3.55–3.75 mm.

Medial eye. Similar to that of adult female and male.

Comparison. The new species is closely related to S. appelloefi Skogsberg, 1920 and S. gallardoi Kornicker, 1971 , but differs in following respects: size of carapace larger, medial eye with 3 sclerotic tubercles (in other species bare), terminally seventh limb with about 13–17 pegs in female and 4 pegs in male (teeth on terminal comb absent).

Distribution and ecology. Southern Ocean, upper bathyal species. It was collected in the Weddell Sea, Prydz Bay and near the Russian Polar Station “Molodezhnaya” at the depths of 239 to 755 m on fine sand ( Fig. 1 ).

Figures

PLATE 1. Scleroconcha tuberculata sp. nov. (Female: A, D – F—MIMB 18275 a; B—MIMB 18275 b; C—MIMB 18275 c). A, B—left and right valves of carapace in lateral view; C, D—ventral view of carapace; E, F—details of sculpture in anterior (near anterior part of middle rib) and central areas of right valve.

FIGURE 1. Distribution map of species of the family Philomedidae in the Antarctic region and adjacent regions from literature and original data.

FIGURE 2. Distribution map of Scleroconcha gallardoi, S. tuberculata sp. nov., and S. species indet.

FIGURE 3. Scleroconcha tuberculata sp. nov. (Female: A, C—MIMB 18275; B, D, E, G—MIMB 18270; F—MIMB 18271; H, J—MIMB 18269; I, K—MIMB 18272). A, B—left valve of carapace in lateral and inside views; C—carapace in ventral view; D—detail of antero-ventral infold of left valve (marginal setae cut); E—detail of setae on left valve, lateral view; F – Idistal part of Bellonci organ; J, K—endopodite of 2 nd antenna.

FIGURE 4. Scleroconcha tuberculata sp. nov. (Female: A, G, I—MIMB 18269; B, F—MIMB 18272; C, D, H—MIMB 18270; E—MIMB 18271). A, B—upper lip, anterior process, medial eye and Bellonci organ; C—medial eye and Bellonci organ; D-G—medial eye and base of Bellonci organ; H—upper lip and anterior process, I—lateral eye.

FIGURE 5. Scleroconcha tuberculata sp. nov. (Female: A, B, D, F, H, J—MIMB 18269; C, I, K— 18272; E, G— 18271; L— MIMB 18270). A—mandible (not all setae shown); B-C—exopodite and details of 1 st endopodial joint and basale of mandible; D—dorsal margin of 2 nd endopodial joint of mandible; E-F—exopodite and detail of 1 st endopodial joint of mandible; G-Ldetail of 2 nd exopodial joint of 5 th limb.

FIGURE 6. Scleroconcha tuberculata sp. nov. (Female: A, C—MIMB 18271; B, D, H—MIMB 18272; E, F—MIMB 18269; G—MIMB 18270). A—exopodial joints 1 – 5 of 5 th limb; B – G—tip of 7 th limb; H—detail of caudal furca.

FIGURE 7. Scleroconcha tuberculata sp. nov. (Male: MIMB 18268). A, B—right and left valve of carapace in lateral view; C—carapace in ventral view; D—rostrum in lateral view; E—infold of rostrum; F—infold of rostrum and anterior detail of carapace; G—pits of middle right valve; H—upper lip, anterior process, medial eye and Bellonci organ; I—distal part of Bellonci organ; J—medial eye and base of Bellonci organ.

FIGURE 8. Scleroconcha tuberculata sp. nov. (Male: MIMB 18268). 2 nd antenna: A—exopodial joint 3 – 9 (setae not shown); B—exopodial joints 1 – 3; C, D—endopodite of left and right limb; E—detail of 3 rd endopodial joint; F— 1 st endopodial joint. Mandible: G, H—basale, exopodite (abnormal on left limb) and endopodite (setae shown only for basale); I—endite of coxale.

FIGURE 9. Scleroconcha tuberculata sp. nov. (Male: MIMB 18268). A, B—exopodite (abnormal on left limb), 1 st endopodial joint and detail of basale; C, D— 2 nd and 3 rd endopodial joints; E—tip of 7 th limb; F—detail of caudal furca; G—lateral eye.

FIGURE 10. Scleroconcha tuberculata sp. nov. (Immature male: A, D, I – L—MIMB 18273; B—MIMB 18274; C, E—ZMH- K- 42259; F—ZMH-K- 42260. Immature female: G, H—ZMH-K- 42261). A – C—left valves of carapace in lateral view; D – Gright valves in lateral view (for panel D ribs not shown); H—carapace in ventral view; I—upper lip, anterior process, medial eye and Bellonci organ; J, K—endopodite of 2 nd antenna; L—tip of 7 th limb.

FIGURE 11. Scleroconcha tuberculata sp. nov. (Immature female: A, B—ZMH-K- 42262; immature male: C – J—ZMH-K- 42259). A—left valve of carapace in lateral view; B—carapace in ventral view; C—infold of rostrum and detail of anterior margin; D, E—infold of caudal process of right valve; F— 1 st and 2 nd joints of 1 st antenna, medial eye and Bellonci organ; Gendopodite and details of protopodite and exopodite of 2 nd antenna; I, H—tip of 3 rd endopodial joint of 2 nd antenna; J—ventroproximal detail of mandible basale.