Philomedes tetrathrix Kornicker, 1975

Chavtur, Vladimir G. & Keyser, Dietmar, 2016, Benthic myodocopid Ostracoda (Philomedidae) from the Southern Ocean, Zootaxa 4141 (1), pp. 1-70 : 58-65

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.

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).

Figures

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

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, 1 st and 2 nd 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 2 nd antenna; K, L—exopodite, dorsal of basale and 1 st 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 1 st and 2 nd joints of 1 st antenna.

FIGURE 38. Philomedes tetrathrix (Male: ZMH-K- 42270). A—medial eye and Bellonci organ, B—terminal part of 1 st antenna (not all setae shown); C—detail of 1 st and 2 nd exopodial joints of 2 nd antenna; D—exopodial joints 7 – 9 of 2 nd antenna; E, F—endopodite of 2 nd antenna; G—detail of 3 rd endopodial joint of 2 nd 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 1 st endopodial joint of mandible; C, D—details of ventral surface of coxale and basale of mandible; E—exopodial joints 1 – 5 of 5 th limb (not all setae on 1 st and 2 nd joints shown); F – H—tip of 7 th 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 2 nd antenna.