Philomedes rotunda Skogsberg, 1920

Chavtur, Vladimir G. & Keyser, Dietmar, 2016, Benthic myodocopid Ostracoda (Philomedidae) from the Southern Ocean, Zootaxa 4141 (1), pp. 1-70 : 54-58

Philomedes rotunda Skogsberg, 1920

( Figs. 34 , 35 )

1920 Philomedes (Philomedes) rotunda Skogsberg : 366, 367, 368, 414, Figs. 75, 76. 1962 Philomedes rotunda Skogsberg, 1920 —Poulsen: 345 [key].

1975 Philomedes rotunda Skogsberg, 1920 —Kornicker: 245–248, Figs. 131, 132 (map), 144–146. 1986 Philomedes rotunda Skogsberg, 1920 —Kempf: 590 (key).

Studied material (coordinates, depth and sediment see Appendix). 52th Russian Antarctic Expedition Prydz Bay, station 7, sample 36: MIMB 18314 —adult female (2.37 mm).

Station 8, sample 37: MIMB 18316—immature male (1.87 mm).

Station 10, sample 54: MIMB 18 312—adult female (2.35 mm).

Station 10, sample 55: MIMB 18 313—adult female (2.50 mm).

Station 12, sample 65: MIMB 18 315—adult female (2.80 mm).

Additional material. See Appendix.

Diagnosis of female ( Kornicker 1975, with additional remarks). Carapace: oval in lateral outline with minute caudal process, surface reticulate, length 1.90–2.80 mm.

First antenna: 2nd joint with 3 setae, 1 ventral, 1 lateral and 1 dorsal.

Second antenna: 1st joint of endopodite with 6 setae, 5 proximal and 1 distal; 2nd joint with 1 long and 0 (usually) or 1 (rarely) short ventral seta and 1 long terminal seta.

Mandible: dorsal margin of basale with 3 setae, 1 near middle and 2 subterminal.

Sixth limb: epipodite with 3–4 setae.

Seventh limb: each limb with 15–26 setae, 2–5 pegs present on opposite terminal comb.

Caudal furca: each lamella with 9–13 claws.

Bellonci organ: 2-jointed, with pointed tip.

Lateral eye: minute, with 2 ommatidia.

Anterior process (above upper lip): developed, large and triangular.

Male unknown.

Supplementary description of adult female. Carapace ( Figs. 34 A–E). Length 1.90–2.30 mm (in literature: 1.90–2.17 mm).

Infold on rostrum with 10–14 setae forming a row. Antero-ventral inside with 10–16 setae and 9–11 striations. Posterior infold with 5–6 short setae. Surface reticulate and with very rare setae.

First antenna ( Fig. 34 I, J, M). Second joint with 3 spinous setae, 1 dorsal, 1 midlength seta and 1 long ventral seta.

Second antenna ( Fig. 34 N, O). First joint with 5 or (usually) 6 setae, 4 or 5 proximal and 1 distal; second joint elongate ( Skogsberg 1920: short and thick (!) as in P. globosa ) and with 1 long spinous ventral seta and 1 midlength subterminal bare seta.

Mandible ( Fig. 35 F–K). Basale: dorsal margin with 3 setae, 1 near middle and 2 subterminal; medial side with 6 setae, 3 pectinate and 3 normal type; lateral surface with 4 (rarely) or 5 setae forming a row parallel to ventral margin; ventral margin with 4 or 5 distal setae. Exopodite somewhat shorter than first endopodial joint ( Fig. 35 G, I). Endopodite: first joint with 4 ventral setae; dorsal margin of second joint with 2–4 setae in proximal group and 5 or (usually) 6 setae in distal group, ventral margin with 1–3 setae in subterminal group and 2–3 in terminal group. Right limb in MIMB 18313 abnormal ( Fig. 35 F, H): coxal endite only with 1 seta and without tooth; lateral surface and ventral margin of basale total with 6 setae, of which 1 stout and pectinate; exopodite short and without setae; endopodite: first joint only with 3 ventral setae, dorsal margin of second joint without setae and ventral margin only with 1 terminal seta; third joint only with 1 peg-like short seta.

Sixth limb. Endite I with 3 terminal and 1 medial setae, endite II with 3 (usually) or 2 terminal and 1 medial setae, endite III with 8 (usually) or 7 terminal and 1 medial setae, endite IV with 6–9 terminal and 1 medial setae, end joint with 17–26 setae; 3–4 setae present in place of epipodial appendage.

Seventh limb ( Fig. 35 L–N). Each limb with 17–20 (in literature: 23–26) setae, 4–5 setae (2+2 or 2+3) in distal group and 12–15 setae (4+8, 5+7, 5+8, 6+9 and 7+8) in proximal group; each seta with 3–6 bells and some wreaths of short, stiff setules, placed obliquely. Terminal comb with 15–18 alate teeth; 2–5 long pegs present on opposite comb.

Caudal furca ( Fig. 30 P). Limb with 10+11, 11+11, 11+12 or 11+13 claws.

Bellonci organ ( Fig. 34 F–J). Organ elongate, 1- or 2-jointed and longer than first joint of first antenna. Its tip pointed or with 1–2 minute spines.

Medial eye ( Fig. 34 I, J). Smooth.

Lateral eye. Small with 2 ommatidia.

Upper lip ( Fig. 34 I–L). Lip ventrally hirsute, terminally blunt, without or with several glandular processes.

Anterior process on body ( Figs. 34 I, J; 35 B–D). Large, triangular and with short or long terminal process.

Supplementary description of A- 1 male. Carapace. Length 1.87 mm.

Second antenna ( Fig. 34 E). Same as that illustrated by Skogsberg (1920: 415, Fig. LXXV-4). Our specimen differs in having only 4 proximal setae on first endopodial joint.

Mandible. Similar to that of adult female.

Sixth limb. Endite I with 3 terminal and 1 medial setae, endite II with 3 or 4 terminal and 1 medial setae, endite III with 8 terminal and 1 medial setae,

endite IV with 8 terminal and 1 medial setae, end joint with 20 setae; 2 or 3 present in place of epipodial appendage.

Seventh limb. Each limb with 15 setae, 4–5 (2+2 or 2+3) distal and 10–11 (4+6 or 5+6) proximal; each seta with 2–4 bells. Terminal comb with 10 alate teeth; 2 or 3 pegs present on opposite comb.

Caudal furca. Limb with 10+10 claws.

Medial eye ( Fig. 35 A). Smooth.

Lateral eye ( Fig. 35 O). Eye developed, with about 17 ommatidia.

Bellonci organ ( Fig. 35 A). Organ elongate, 1-jointed, terminally with minute process and some spines.

Upper lip ( Fig. 35 A). As in adult female.

Anterior process on body ( Fig. 35 A). Large, triangular.

Distribution and ecology. Subantarctic-antarctic sublitoral species. It was collected in South Georgia ( Skogsberg 1920; Kornicker 1975), Weddell Sea and Prydz Bay (present study) between 54° and 71° S ( Fig. 31 ) districts of the Antarctic at depths of 7 to 237 m, on hard and soft substrates: rock, stone, gravel, muddy sand and clay bottom with scattered algae.

Figures

FIGURE 30. Philomedes charcoti (Male: MIMB 18306). A—detail of reticulation in central area of right valve in lateral view; B—medial eye and Bellonci organ; C—upper lip, anterior process, medial eye, Bellonci organ, 1 st and 2 nd joints of 1 st antenna; D—seta of 5 th joint of 1 st antenna; E—endopodite of 2 nd antenna; F— 2 nd endopodial joint of 2 nd antenna; G—details of coxale and basale of mandible; H, I—exopodite, 1 st endopodial joint and detail of basale of mandible; J—coxale endite of mandible; K—copulatory appendage and caudal furca; L, M—lateral eye.

FIGURE 31. Distribution map of Philomedes orbicularis, P. rotunda and P. tetrathrix

FIGURE 34. Philomedes rotunda (Female: A, M, N—MIMB 18314; B, F, K—MIMB 18313; D, E, G, J, L, O—MIMB 18312; C, H, I, P—MIMB 18315). A – C—left valve of carapace in lateral view; D—right valve in lateral view; E—detail of reticulation in central area of left valve in lateral view; F—Bellonci organ; G, H—distal part of Bellonci organ; I, J—upper lip, anterior process, medial eye, Bellonci organ, 1 st and 2 nd joints of 1 st antenna; K, L—upper lip; M— 2 nd joint of 1 st antenna; N, O—endopodite of 2 nd antenna; P—caudal furca.

FIGURE 35. Philomedes rotunda (Immature male: A, E, O—NINB 18316; female: B, F, H, J, K – M—MIMB 18313; C, G, I— MIMB 18312; D, N—MIMB 18315). A—upper lip, anterior process, medial eye, Bellonci organ; B – D—anterior process of body; E—endopodite of 2 nd antenna; F—abnormal left mandible (dorsal setae not shown); G—exopodite and dorsal part of basale and 1 st endopodial joint of mandible; H—exopodite (abnormal) and 1 st endopodial joint of left mandible; I—exopodite (normal) of mandible; J—ventral arming of mandibular basale (abnormal); K—ventral pectinate seta of mandibular basale; L – N—tip of 7 th limb; O—lateral eye.