Benthic myodocopid Ostracoda (Philomedidae) from the Southern Ocean Author Chavtur, Vladimir G. Author Keyser, Dietmar text Zootaxa 2016 4141 1 1 70 journal article 10.11646/zootaxa.4141.1.1 5f6dfb77-a313-4996-b2c8-1f944ab63ad7 1175-5326 260445 6033C3F3-85B8-4665-A7AF-7C0E4B230ABC Philomedes tetrathrix Kornicker, 1975 ( Figs. 36–40 ) 1975 Philomedes tetrathrix Kornicker : 255–262, Figs. 131, 132 (map), 151–156. 1990 Philomedes cf. P. tetrathrix Kornicker, 1975 —Hartmann: 199. Studied material (coordinates, depth and sediment see Appendix). RV “Polarstern”PS 61 ANT XIX/3, station 46- 7: ZMH-K-42271—immature female ( 2.12 mm ) and ZMH-K-42272—immature male ( 2.05 mm ); ZMH-K- 42273—immature male ( 2.22 mm ). ANT XIX/4, station 141-9: ZMH-K-42270—adult male ( 3.47 mm ). Station 143-1: ZMH-K-42269—adult female ( 2.46 mm ). Diagnosis of female ( Kornicker 1975, with additional remarks ). Carapace : with truncate posterior, length 1.92–2.78 mm . First antenna : 2nd joint with 2 setae, 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 2–3 short ventral setae and 1 long terminal seta. Mandible : dorsal margin of basale with 5 setae, 3 near middle and 2 subterminal. Sixth limb : epipodite with 3 setae. Seventh limb : each limb with 23–33 setae, 5 distal and 21–28 proximal; 2–3 pegs present on opposite terminal comb. Caudal furca : each lamella with 10 claws. Bellonci organ : 1-jointed, with rounded tip. Lateral eye : small, with 2–3 ommatidia or only with pigment. Anterior process (above upper lip): developed, large, horn-like and curved. Diagnosis of male. Carapace : length 3.47 mm . First antenna : 2nd joint with 2 setae, 1 lateral and 1 dorsal. Second antenna : 1st joint of endopodite with 6 seta, 5 proximal and 1 distal; proximal seta of 3rd joint thin about 1/3 (or shorter) of the joint’s length. Mandible : dorsal margin of basale with 5 setae, 3 near middle and 2 subterminal; coxale endite absent. Sixth limb : epipodite with 3 setae. Seventh limb : each limb with 25–26 seta, 5 distal and 20–21 proximal; 2 or 3 pegs present on opposite terminal comb. Caudal furca : each lamella with 8 claws. Bellonci organ : 1-jointed, with rounded tip. Anterior process (above upper lip): developed, large, with terminal crank-like process. Supplementary description of adult female. Carapace (36 A). Length 2.40 mm . Carapace with truncate posterior. Infold on rostrum with 12–15 setae. Antero-ventral inside with 5–9 setae ( 16–18 in Kornicker 1975 ) and 15 striations. Posterior infold with 5 setae. Carapace with distinct small reticulate structure ( Kornicker 1975: 256— “faint reticulate structure visible in transmitted light” ). First antenna ( Fig. 36 D). Second joint with 2 setae, 1 dorsal and 1 lateral. Second antenna ( Fig. 36 I, J). First joint of exopodite with short disto-medial spine. Second endopodial joint with 5 setae ( 4 in Kornicker 1975 ), 1 long spinous and 3 short bare ventral setae and 1 reflexed terminal seta. Mandible ( Fig. 36 K, L). Basale: dorsal margin with 5 setae; medial side with 6 setae, 3 pectinate and 3 usual type ; lateral surface with 5 setae forming a row parallel to ventral margin; ventral margin with 3 distal setae. Endopodite: first joint with 4 ventral setae; dorsal margin of second joint with 2 setae in distal group, 5 setae ( 6 in Kornicker 1975 ) in proximal group and 1 seta between these groups, and ventral margin with 2 or 3 setae in distal group and 3 setae in subterminal group. Sixth limb . Endite I with 2 terminal and 1 medial setae, endite II with 3 terminal and 1 medial setae, endite III with 7 or 8 terminal and 1 medial setae, endite IV with 8 terminal and 1 medial setae, end joint with 28; 3 setae present in place of epipodial appendage. Seventh limb . Each limb with 23–25 setae, 5 (3+2) distal setae and 18–20 (6+12 or 9+11) proximal setae; each seta with 3–7 bells. Terminal comb with 10–11 alate teeth; 2 pegs present in place of epipodial appendage. Caudal process . Limb with 10+10 claws. Bellonci organ ( Fig. 36 D). Elongate, 1-jointed, with rounded tip and somewhat shorter than first joint of first antenna. Medial eye ( Fig. 36 D, F). Large, pigmented. Lateral eye ( Fig. 36 D). Eye small, slightly pigmented, without ommatidia. Upper lip ( Fig. 36 D, G, H). Ventrally hirsute, terminally blunt, with several glandular processes. Anterior process on body ( Fig. 36 D). Process large, horn-like. Description of adult male. Carapace ( Figs. 36 B, C; 37 A–E). Length 3.47 mm . Carapace with truncate posterior and oval caudal process. Infold on rostrum with 24 setae forming L-shaped row, and 1 minute seta present on infold posterior to incisure. Anteroventral inside with 6–8 setae. Posterior infold with 5 or 7 minute spines ( Figs. 37 C, D). Carapace with faint small reticulate structure visible in transmitted light ( Fig. 36 C). First antenna ( Figs. 36 E; 37 G; 38 B, C). Second joint with 1 dorsal and 1 lateral setae. Sensory setae of fifth joint with knee near middle and 5 terminal filaments ( Fig. 38 B). Second antenna ( Fig. 38 D–G). Exopodite: first joint with long and short, thin and thick distal spines on lateral surface and sclerotized rounded process on terminal margin ( Fig. 38 C); ninth joint with 5 setae, 3 long and 2 short ( Fig. 38 D). Endopodite: first joint with 5 proximal and 1 distal setae. Second joint with 3 short setae, 2 stout and 1 normal type ; 2 muscles bands, both extend from middle of this joint to proximal margin of third joint. Third joint with relatively short proximal seta (about 1/3 or somewhat shorter than length of joint), 2 minute subterminal setae and about 8 terminal ridges; lateral surface of distal part wrinkled ( Fig. 38 E, G). Mandible ( Fig. 39 A–D). Coxale endite reduced ( Fig. 39 C, D). Basale: dorsal margin with 5 setae; medial side with 6 setae; lateral surface with 4 setae forming a row parallel to ventral margin; ventral margin with 2 or 3 distal setae. Exopodite: about 2/5 length of first endopodial joint. Endopodite: first joint with 5 ventral setae; dorsal margin with 2 setae in distal group, 6 setae in proximal group and 1 seta between these groups, ventral margin with 3 setae in subterminal and 3 in terminal groups. Fifth limb ( Fig. 39 E). First and second joints on exopodite each with 1 elongate evenly tapering hirsute flat tooth and 3 setae; third joint with 3+2 setae; fourth plus fifth joints in total with 6 setae. Endite I with 4 setae, endite II with 8 setae and endite III with 10 setae. Sixth limb . Endite I with 2 terminal and 1 medial setae, endite II with 3 terminal and 1 medial setae, endite III with 7 terminal and 1 medial setae, endite IV with 7 terminal and 1 medial setae, end joint with 18 setae; 3 setae present in place of epipodial appendage. Seventh limb ( Fig. 39 F–H). Each limb with 25–26 setae, 5 (2+3) distal setae and 20–21 (10+10 or 10+11) proximal setae; each seta with 4–8 bells. Terminal comb with 10 alate teeth; 2 or 3 pegs present on opposite comb. Caudal furca ( Fig. 40 A, B). Limb with 8+8 claws. Each lamella elongate and slim. Copulatory appendage ( Fig. 40 A–C). Limb longer than half length of furcal lamella. Each lobe with some setae. Bellonci organ ( Figs. 36 E; 38 A). Elongate, 1-jointed, with rounded tip and shorter than first joint of first antenna. Medial eye ( Figs. 36 E; 38 A). Eye large and pigmented. Lateral eye ( Fig. 38 H). Eye large and pigmented. FIGURE 36. Philomedes tetrathrix (Female: A, D, F–L—ZMH-K-42269; B, C, E—ZMH-K-42270). A—left valve of carapace in lateral view; B—right valve in lateral view; C—detail of reticulation in central area of right valve in lateral view; D, E—upper lip, anterior process, medial and lateral eyes (lateral eye not shown on panel E), Bellonci organ, 1st and 2nd joints of antenna; F—tip of medial eye and base of Bellonci organ; G—anterior process of body; H—upper lip; I, J—endopodite of 2nd antenna; K, L—exopodite, dorsal of basale and 1st endopodial joint (all joints shown on panel K) of mandible. FIGURE 37. Philomedes tetrathrix (Male: ZMH-K-42270). A—infold of anterior part of left valve of carapace; B—anterior part of right vale in lateral view; C, D—infold of caudal process of right and left valves; E—detail of infold on caudal process of left valve; F—upper lip and anterior process of body; G—detail of 1st and 2nd joints of 1st antenna. FIGURE 38. Philomedes tetrathrix (Male: ZMH-K-42270). A—medial eye and Bellonci organ, B—terminal part of 1st antenna (not all setae shown); C—detail of 1st and 2nd exopodial joints of 2nd antenna; D—exopodial joints 7–9 of 2nd antenna; E, F—endopodite of 2nd antenna; G—detail of 3rd endopodial joint of 2nd antenna; H—lateral eye. FIGURE 39. Philomedes tetrathrix (Male: A–E, G, H—ZMH-K-42270; F—ZMH-K-42269). A, B—basale, exopodite and 1st endopodial joint of mandible; C, D—details of ventral surface of coxale and basale of mandible; E—exopodial joints 1–5 of 5th limb (not all setae on 1st and 2nd joints shown); F–H—tip of 7th limb. FIGURE 40. Philomedes tetrathrix (Male: A–E, G, H—ZMH-K-42270; female: F—ZMH-K-42269). A, B—copulatory appendage and caudal furca (detail on panel B); C—limb of copulatory appendage; D–F—right valves in lateral view; G, Hendopodite of 2nd antenna. Upper lip ( Figs. 36 E; 37 F). Terminally rounded with some glandular processes. Anterior process on body ( Figs. 36 E; 37 F). Process relatively large, rounded and terminally with long curved process. Supplementary description of A- 2 male . Carapace ( Fig. 40 E, F). Length 2.05–2.22 mm . Infold in rostrum with 14 setae forming L-shaped row. Antero-ventral inside with 5 setae and 15 striations. Posterior infold with 3 minute spines. Carapace smooth, without visible ornamentation. Height of posterior half of carapace slightly more than that of anterior half. Second antenna ( Fig. 40 G, H). Endopodite: first joint with 3 proximal and 1 distal setae (right endopodite aberrated: see Fig. 40 G); second joint with 1 long spinous and 1 short bare ventral setae; third joint with 1 midlength dorsal and 1 short terminal setae. Mandible . Basale: dorsal with 4 setae, 2 near middle and 2 subterminal, medial side with 3 pectinate and 3 regular setae, lateral surface with 4 setae, ventral margin with 2 distal setae. Endopodite: first joint with 4 ventral setae; dorsal margin of second joint with 2 setae in distal group, 6 setae in proximal group and 1 seta between these group. Seventh limb . Limb with 27 setae, 5 (3+2) distal setae and 22 (11+11) proximal setae. 2 pegs present on opposite terminal comb. Caudal furca . Limb with 8+8 claws. Medial eye , upper lip anterior and process on body . Similar to that of adult female. Remarks . Our specimen of an adult female differs from females described by Kornicker (1975) in the following: carapace with distinct reticulate structure, less setae on antero-ventral inside of carapace and presence of 4 setae on ventral margin of second endopodial joint of second antenna. Distribution and ecology . Subantarctic-antarctic sublitoral-abyssal species. It has been collected in the Atlantic Sector of the Southern Ocean between 43° and 62°S ( Fig. 31 ) at depths of 146 to 3382 m ( Kornicker 1975 ; Hartmann 1990 ; present study) on soft substrates: volcanic sand, medium-to-coarse sand and small pebbles ( Kornicker 1975 ).