Philomedes rotunda Skogsberg 1920

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.