dcsimg

Comprehensive Description

provided by Smithsonian Contributions to Zoology
Philomedes subantarctica

HOLOTYPE.—USNM 127977, gravid ♀, length 2.70 mm. Valves and some appendages in alcohol, remaining appendages on slides.

TYPE-LOCALITY.—Eltanin Cruise 6, station 340, Subantarctic.

PARATYPES.—USNM 127978, adult ♀; USNM 128040, 128041, 2 adult ♂ ♂; USNM 128042, 7 juveniles, all from same sample as holotype.

ADDITIONAL SPECIMENS.—USNM 137376, gravid ♀; USNM 137377, 1 gravid ♀, 2 adult ♀ ♀, 4 juveniles; USNM 137383, adult ♀; USNM 137384, 1 juvenile. USNM 137376, 137377 from Vema Cruise 14, station V–14–2; USNM 137383, 137384 from Vema Cruise 18, V–18–12. USNM 138034, 1 adult ♀ with distorted carapace, length about 2.93 mm, height about 1.72 mm, + 1 juvenile, both from Eltanin Cruise 6, station 354.

DIAGNOSIS OF FEMALE.—Posterior with small caudal process; length 2.60–2.70 mm; surface with abundant short stout hairs.

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

Second antenna: 1st endopodial joint with 8 or 9 bristles, 2nd with 5.

Mandible: Dorsal margin of basale with 5 or 6 bristles.

Sixth limb: Each limb with about 42 bristles on end joint.

Seventh limb: Each limb with 27 or 28 bristles; terminus with about 11 short pegs opposite comb (pegs arranged in circle with slightly longer peg in middle).

Furca: Each lamella with 10 or 11 claws.

DESCRIPTION OF FEMALE (Figures 157–161).—Carapace with prominent rostrum, broad incisur and small caudal process; ventral margin more rounded than dorsal margin; anterior and inferior corners of rostrum evenly rounded; anterior margin of rostrum straight with small protuberance at lower end (Figures 157, 158a-i, 160).

Ornamentation: Carapace smooth but with minute pores visible under high magnification; short stout hairs abundant; few long hairs with broad base scattered over valve surface and along ventral margin.

Infold (Figure 158c,e,g-i): Infold broad along anterior, ventral, and lower part of posterior margins; infold on rostrum with 26 or 27 bifurcate, spinous bristles; 1 small bristle present on infold posterior to incisur; anteroventral part with 11 striae and 17 spinous double bristles; infold along ventral margin bare; ridge paralleling inner margin of posteroventral and posterior infold with about 57 bristles in groups of 1 to 5 bristles; “pocket” present in infold of caudal process; anterior margin of “pocket” with 9 to 12 short bare bristles; posterior margin of “pocket” with 5 or 6 short bare bristles along upper half; 4 or 5 short bristles present on posteroventral infold between its outer margin and ridge with 57 bristles.

Selvage: Lamellar prolongation striate, fringed, with additional long hairs with bases at middle of lateral side of anteroventral prolongation.

Size (Figure 131): USNM 127977, length 2.70 mm, height 1.88 mm; USNM 127978, length 2.63 mm, height 2.02 mm; USNM 137376, length 2.60 mm, height 1.88 mm; USNM 137383, length 2.68 mm, height 1.88 mm.

First antenna: 1st joint with spines forming clusters on lateral surface near distodorsal corner, and on medial surface near distoventral corner; 2nd joint with spines along dorsal margin and on lateral surface near distodorsal corner and with 3 spinous bristles, 1 ventral, 1 dorsal, 1 lateral; 3rd joint with 3 terminal bristles, 1 spinous ventral, 2 dorsal (1 short bare, 1 longer spinous); 4th joint with 5 terminal spinous bristles, 4 ventral, 1 dorsal; sensory bristle of 5th joint with 5 short proximal filaments and 3 longer terminal filaments not including stem; medial bristle of 6th joint with long proximal and short distal marginal spines. Seventh joint: a-bristle similar to bristle of 6th joint but slightly longer; b-bristle proximal part obscure, distal part with 3 long filaments excluding tip; c-bristle with 4 short proximal filaments and 3 terminal filaments excluding stem. Eighth joint: d- and e-bristles bare; f-bristle with 3 proximal and 3 terminal filaments excluding stem; g-bristle with 3 proximal and 4 terminal filaments excluding stem; filaments of all bristles bare.

Second antenna (Figure 158j-l): Protopodite bare. Endopodite 2-jointed: 1st joint with 8 or 9 bare bristles forming 2 groups, proximal group with 5 or 6 bristles, distal group with 2 to 4; 2nd joint with 4 ventral bristles with wreaths of long spines and 1 recurved bare terminal bristle. Exdopodite: 1st joint with small distomedial spine; bristles of 2nd to 9th joints bare; bristles on 6th to 8th joints broken; joints 3 to 8 with small basal spines; distal margins of joints 2 to 8 with short spines forming row; joint 9 with 7 bristles, 5 long broken, 2 shorter bare.

Mandible (Figure 158m): Coxale endite spinous with bifurcate tip and small bristle near base. Basale: dorsal margin with 5 or 6 bristles, 3 or 4 near middle, 2 terminal, all with wreaths of long spines; medial surface with 6 proximal bristles near ventral margin, 3 stout pectinate, 3 slender with wreaths of long spines; ventral margin with 3 or 4 distal long bristles with wreaths of long proximal spines and short distal spines; lateral surface with 7 to 9 bristles oriented venteriad, these form row approaching ventral margin proximally (the proximal bristle being on, or very close to, ventral margin). Exopodite about 80 percent length of dorsal margin of 1st endopodite joint, hirsute near pointed tip, outer bristle with short marginal spines, inner longer bristle with proximal wreaths of long spines and distal short spines (exopodite of right mandible of USNM 127977 aberrant with 3 bristles, all with proximal wreaths of long spines and short distal spines). Endopodite: ventral margin of 1st joint with 4 terminal bristles, 2 long, 2 short; dorsal margin of 2nd joint with 5 or 6 bristles in proximal group and 6 in distal group; ventral margin with 3 bristles in both proximal and distal groups; end joint with 3 claws and 4 bristles; surface of coxale, basale, and 2nd endopodite joint with spines forming clusters.

Maxilla (Figure 158n): Endite I with 11 bristles, endite II with 6, and endite III with 1 proximal and about 8 distal bristles. Exopodite very short with 3 bristles: proximal bristle short with short marginal spines; terminal bristles with long proximal and short distal spines. Distal margin of basale with 3 bristles. Endopodite: 1st joint spinous with spinous α-bristle, β-bristles obscure; end joint with 5 spinous a-bristles, 2 b-bristles (anterior of these spinous, posterior clawlike), c-bristles obscure, 3 d-bristles (2 anterior bristles clawlike).

Fifth limb (Figure 159a-c): Epipodial appendage with 62 bristles. Exopodite 1st joint: triangular protuberance in front of main tooth with proximal node on medial margin; 4 teeth of main tooth with secondary teeth along medial margin. Exopodite 2nd joint: large triangular tooth with 2 nodes on medial margin; lateral corner with indication of socket but without minute bristle; posterior side with usual stout bristle and group of 3 bristles distal to it. Exopodite 3rd joint: medial lobe with 3 spinous bristles, one of these also pectinate; outer lobe with 2 bristles with long slender proximal spines and short distal spines. Fourth and 5th joints fused, with 6 spinous bristles.

Sixth limb (Figure 159d): Epipodial appendage with 5 hirsute bristles; 1st endite with 3 bristles, 1 short medial, 2 terminal (1 long, 1 short—the short terminal bristle is medial to longer bristle); 2nd endite with 4 bristles, 1 medial, 3 terminal; 3rd endite with 9 bristles, 1 medial, 8 terminal; 4th endite slightly narrower than 3rd endite and with 9 bristles, 1 medial, 8 terminal; end joint with 42 marginal bristles (about 15 medial, 9 lateral, 18 ventral); all bristles on limb with marginal hairs or spines; medial and lateral surfaces of end joint and lateral surfaces of endites I to IV extremely hirsute; end joint extending posteriorly.

Seventh limb (Figure 159e): Each limb with 27 or 28 bristles, 5 in distal group (3 dorsal, 2 ventral) and 22 or 23 proximal (8 ventral, 14 or 15 dorsal); each bristle with 3–6 bells and distal marginal spines; end comb with 13 or 14 alate teeth plus middle recurved longer tooth; 11 short pegs on dorsal side opposite comb (pegs arranged in circle with slightly longer peg in middle).

Furca (Figure 159f): Usual type for genus with all claws separated from lamella by suture and decreasing in length and stoutness proximally along lamella; each lamella with 10 or 11 claws; teeth in medial row of claw 1 slightly larger than those in lateral row and teeth near middle of row larger than those at either end; long hairs present at inner bases of claws and following last claw.

Eyes and rod-shaped organ (Figure 159g,h): Lateral eye minute with 3 small ommatidia; medial eye large, bare, pigmented; rod-shaped organ elongate, 2-jointed, with rounded tip bearing minute spine (always?).

Upper lip (Figure 159g): Lip hirsute with several anterior spines; single rounded process present between lip and medial eye.

Posterior (Figure 159i): Posterior margin and area hirsute.

Eggs: USNM 127977 and 137376 with 23 eggs.

Parasites (Figures 159j, 161): Segmented filaments attached to terminus of 7th limbs between comb, and cup-shaped stalked protistans attached to carapace near incisur and caudal process. USNM 137383 with 1 choniostomatid ♂ and ♀ and 5 choniostomatid ovisacs.

DESCRIPTION OF ADULT MALE (Figure 162).—Carapace in lateral view more elongate than that of female and with shallow incisur. Selvage and distribution of bristles on infold more or less similar to those on that of female. Carapace smooth but with minute pores and faint reticulations visible in transmitted light. Long hairs with broad bases and shorter slender hairs scattered over valve surface and along margins; short stout hairs abundant on the female carapace absent on the male (Figure 162a-c).

Size (Figure 131): USNM 128040, length 2.65 mm, height 1.48 mm; USNM 128041, length 2.70 mm, height 1.61 mm (not dissected).

First antenna: 1st joint bare; 2nd joint spinous with 2 bristles with short marginal spines, 1 bristle dorsal, subterminal, 1 lateral near ventral margin, also subterminal; 3rd joint separated from 4th by suture and with 1 ventral bristle with long proximal and short distal spines, and 2 spinous dorsal bristles (1 very short with short marginal spines, 1 longer with proximal long spines and distal short spines); 4th claw short with 1 dorsal bristle with proximal long spines and distal short spines, and 4 ventral bristles, all with short marginal spines, some also with few proximal long spines; sensory bristle of minute 5th joint with numerous thin filaments on broad base (distal part of bristle broken); bristle of 6th joint about twice length of combined 7th and 8th joints and with proximal long spines and distal short spines. Seventh and 8th joints: a-bristle shorter than bristle of 6th joint and with short marginal spines; b- and g-bristles broken; long c- and f-bristles broken, with 10 to 12 short filaments on remaining part, filaments bifurcate at tip; d- and e-bristles bare.

Second antenna (Figure 162e): Protopodite bare. Endopodite 3-jointed: 1st joint with 7 or 8 bristles forming 2 groups, proximal group with 5 bare bristles, distal group with 2 or 3 bristles, some or all with long proximal marginal spines; 2nd joint with 3 ventral bristles with short marginal spines, proximal bristle more slender than others; 3rd joint with slender proximal bristle and 2 short subterminal bristles, tip of joint with 5 or 6 ridges. Exopodite: 1st joint with few slender spines along ventral margin and small medial terminal spine; bristle of 2nd joint reaching 5th joint and with 4 small spines near middle of ventral margin; joints 2 to 8 with short spines forming row along terminal margin; joint 3 longer than joint 2; small basal spines present on joints 3 or 4 to 8; 9th joint with 4 long medial bristles and 2 short lateral bristles; bristles of joints 3 to 9 with natatory hairs and without spines.

Mandible (Figure 162f): Coxale endite reduced, bifurcate, with short bristle near base about length of endite. Basale: medial surface with 6 proximal bristles, all with short marginal spines; ventral margin with 3 bristles distal to middle, all with long proximal and short distal spines; lateral surface with 5 or 6 bristles oriented venteriad, these form row approaching ventral margin proximally (proximal bristle actually on ventral side of margin on specimen examined), all bristles with long proximal and short distal spines; dorsal margin with 5 or 6 bristles (3 or 4 short bristles near middle with short marginal spines, 1 short terminal with short marginal spines, 1 long terminal with long spines near middle). Exopodite about 70 percent length of dorsal margin of 1st endopodite joint, hirsute at tip, shorter outer bristle and longer inner bristle both with short marginal spines. Endopodite: ventral margin of 1st joint with 5 long bristles, 1 or 2 of these with short marginal spines, remaining with long proximal and short distal spines; dorsal margin of 2nd joint with 2 groups of bare bristles, about 5 bristles in proximal and 6 in distal group; ventral margin with 3 bristles in both proximal and distal groups; claws and bristles of end joint missing; medial surfaces of basale and 2nd endopodite joint with short spines forming clusters.

Maxilla (Figure 162g): Limb reduced; plumose bristle of coxale unusually long and broad; exopodite small with usual 3 spinous bristles.

Fifth limb (Figure 162h): Usual type for genus. Exopodite: outer lobe of 3rd joint with 2 stout plumose bristles, inner lobe with 3 bristles; 4th plus 5th joints with 6 bristles.

Sixth limb (Figure 162i): Epipodial appendage with 4 hirsute bristles; 1st endite with 3 bristles, 1 short medial, 2 terminal (1 long, 1 short); 2nd endite with 4 bristles, 1 medial, 2 terminal; 3rd endite with 9 bristles, 1 medial, 8 terminal; 4th endite with 10 bristles, 1 medial, 9 terminal; 4th endite very slightly narrower than 3rd; end joint with 26 to 29 bristles; lateral surfaces of endites 2 to 4, and medial and lateral surfaces of end joint hirsute.

Seventh limb (Figure 162j): Each limb with 25 or 26 bristles, 5 in distal group (2 ventral, 3 dorsal) and 20 or 21 in proximal group (7 or 8 ventral, 12 or 13 dorsal); each bristle with 3 to 5 bells and distal marginal spines; end comb with 10 teeth plus longer middle tooth; margins of teeth obscure, but seem spined; 8 short pegs on dorsal side opposite comb (pegs arranged in circle with longest peg in middle).

Furca: Each lamella with 9 claws, otherwise similar to that of female.

Eyes and rod-shaped organ (Figure 162k,l): Lateral eye large with about 42 ommatidia and black pigment between them; medial eye similar to that of female; rod-shaped organ elongate, 2-jointed with tip drawn out in slender spine.

Upper lip (Figure 162k): Lip similar to that of female except without hairs.

Posterior margin: Similar to that of female.

Copulatory organ (Figure 162m,n): Organ very small with 2 lobes, shorter lobe with 3 bristles; longer lobe with 2 bristles on end joint.

Parasites: None.

DESCRIPTION OF JUVENILE, USNM 138034.—Seventh limb: see Figure 163.

SEXUAL DIMORPHISM.—In addition to usual difference in shape, male carapace does not have abundant short stout hairs present on female. Lateral surface of basale of mandible bears only 5 or 6 bristles compared to 7 to 9 on female’s mandible. End joint of the 6th limb bears 26 to 29 bristles compared to 42 bristles on 6th limb of female. Dorsal margin of terminus of 7th limb bears only 8 pegs compared to 11 on 7th limb of female.

COMPARISONS.—The carapace outline and details of the caudal process of the new species resemble Philomedes lilljeborgi (G. O. Sars, 1865), (see Skogsberg, 1920:402 for detailed description of P. lilljeborgi). The 7th limbs differ in that those of P. lilljeborgi bear 10 to 12 bristles, whereas, the 7th limbs of P. subantarctica have 25 to 28 bristles. The pegs on the dorsal margin of the terminus of the 7th limbs also differ in their distribution—those on P. lilljeborgi form 2 rows, whereas, those on P. subantarctica form a circle with 1 central peg. The 6th limb of the female P. subantarctica bears about 42 bristles on the end joint compared to 28–33 for P. lilljeborgi. The large number of bristles (8 or 9 on female; 7 or 8 on male) on the 1st joint of the endopodite of the 2nd antenna of P. subantarctica may also be significant because no more than 6 have been described on this joint of P. lilljeborgi.

Poulsen (1962:346) identified a male ostracod as Philomedes lilljeborgi (Sars). The high number of bristles (27–30) on the 7th limb and the low number of bristles (3) on the dorsal margin of the basale of the mandible on that specimen suggest that it is not conspecific with P. lilljeborgi. Poulsen’s specimen differs from P. subantarctica in having fewer bristles on the 1st joint of the endopodite of the 2nd antenna, a separation between the distal 2 bristles of the 2nd joint of the endopodite, and more bristles on the dorsal margin and lateral surface of the basale of the mandible.

DISTRIBUTION.—This species was collected east of Argentina in both Subantarctic and Subantarctic-to-35°S regions at depths of 129 to 1976 m (Figure 132).
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bibliographic citation
Kornicker, Louis S. 1975. "Antarctic Ostracoda (Myodocopina) Parts 1 and 2." Smithsonian Contributions to Zoology. 1-720. https://doi.org/10.5479/si.00810282.163