"Philomedes species A, Kornicker, 1971:192, fig. 17 [?].
HOLOTYPE—USNM 126219, gravid female, length 1.68 mm. Valves and some appendages in alcohol, remaining appendages on slides.
TYPE-LOCALITY—USCGC Glacier Cruise 2, station 0009, Weddell Sea.
ETYMOLOGY—The specific name "heptathrix" from the Greek "hepta" [= seven] and "thrix" [ = hair] refers to the 7 bristles on the dorsal margin of the mandibular basale on many specimens, and on the 1st endopodial joint of the 2nd antenna.
PARATYPES—USNM 126220, adult male; USNM 126221, gravid female; USNM 126222, adult female; USNM 126223, adult male; USNM 126224, 48 adult males, 53 adult females,481 juveniles; USNM 127276, adult female. Paratypes from same sample as holotype.
ADDITIONAL SPECIMENS—USNM 127251, adult female; USNM 127256, 3 juveniles, USNM 127255, adult female; USNM 127257, adult female; USNM 127258, adult female (not dissected) + adult male; USNM 127490, adult female; USNM 127493, gravid female; USNM 127494, adult male. USNM 127251 from IWSOE, USCGC Glacier Cruise 2, station 0007; USNM 127255, 127256, same cruise, station 0002; USNM 127257, 127258, same cruise, station 0008; USNM 127490, 127493, 127494, from Deep Freeze I, USS Edisto, stations 5, 6, 8 combined.
DIAGNOSIS OF FEMALE—Posterior rounded with narrow caudal process; length 1.60-1.78 mm.
First antenna: 2nd joint with 3 bristles, 1 ventral, 1 dorsal, 1 lateral.
Second antenna: 1st joint of endopodite with 7 bristles, 2nd with 5.
Mandible: Dorsal margin of basale with 6 or 7 bristles.
Seventh limb: Each limb with 9-12 bristles; 2 or 3 pegs present opposing terminal comb.
Furca: Each limb with 10 or 11 claws.
Lateral eye: Small with 2 or 3 ommatidia.
DESCRIPTION OF FEMALE—Carapace oval in lateral view with prominent rostrum and broad incisur; posterior rounded with narrow caudal process; anterior corner of rostrum rounded, inferior corner more acute and with minute protuberance at tip; anterior margin of rostrum straight.
Infold: Infold broad along anterior and posterior parts of valve, narrow ventrally; infold on rostrum with 19 long bristles forming L-shaped row, some with faint marginal spines; 1 small bristle present on infold posterior to incisur; anteroventral part with 9 or 10 striae and 17 short bristles; no bristles observed on ventral infold except near posterior; posterior infold with inner row of about 21 minute bristles, middle row of about 9 short bristles, and outer row of about 8 somewhat stouter bristles just within posterior edge of valve.
Marginal pore canals: Numerous canals present along anterior ventral and posterior margins leading to minute bristles or pores along valve edge and to longer bristles on outer surfaces of valve near edge.
Selvage: Lamellar prolongation with marginal fringe present along anterior, ventral, and posterior margins; prolongation with typical segmentation along rostrum, incisur, and ventral margin; medial surface of prolongation below incisur and along anteroventral margin with long hairs in addition to marginal fringe.
Ornamentation: Carapace smooth but with faint reticulations; bristles present on anterior, ventral, and posterior margins and sparsely distributed on lateral surface.
Size: USNM 126219, gravid female, length 1.68 mm, height 1.19 mm; USNM 126221, length 1.73 mm, height 1.25 mm; USNM 127251, length 1.78 mm, height 1.28 mm; USNM 127255, length 1.78 mm, height 1.32 mm; USNM 127257 (right valve dimensions), length 1.78 mm, height 1.23 mm; USNM 127258, length 1.75 mm, height 1.26 mm; USNM 127490, length 1.60 mm, height 1.29 mm; USNM 127493, length 1.73 mm, height 1.36 mm.
First antenna: Spines forming clusters present on 1st, 2nd, medial surface on 3rd and 5th joints; 2nd joint with 3 bristles, 1 ventral, 1 dorsal, 1 lateral, all with wreaths of long spines proximally and faint short spines distally; 3rd joint with 3 bristles, 1 ventral, 2 dorsal; 4th joint with 5 bristles, 4 ventral, 1 dorsal; 5th to 8th joints normal for genus.
Second antenna: Protopodite spinous along ventral and dorsal margins and on medial surface inward from margins. Endopodite 2-jointed: 1st joint with 7 bristles, 5 in proximal group, 2 in distal group; 2nd joint with 4 ventral bristles, 1 long with long proximal and short distal spines, 3 short with faint short marginal spines, and 1 recurved terminal bristle. Exopodite: bristles of joints 6 to 8 and 4 long bristles of joint 9 broken; bristles of joints 2 to 5 with spines forming row along middle of ventral margin and without natatory hairs; 9th joint with 7 bristles, 4 long, broken, bare, 3 short, unequal in length, with short marginal spines; small medial spine present on distal margin of 1st joint; joints 2 to 8 with several rows of short spines on medial surface and small basal spines.
Mandible: Coxale endite spinous with bifurcate tip and small bristle near base. Basale: dorsal margin with 6 or 7 bristles; medial surface with 5 or 6 (usually 6) proximal bristles near ventral margin, 2 or 3 (usually 3) stout pectinate, 3 slender; ventral margin with 3 (rarely 4) distal bristles; lateral surface with 5 slender bristles oriented venteriad. Exopodite about 80 percent length of dorsal margin of 1st endopodite joint, hirsute near pointed tip; both inner and outer bristle with short marginal spines. Endopodite: ventral margin of 1st joint with 4 terminal bristles; dorsal margin of 2nd joint with 3 bristles in proximal group and 5 or 6 in distal group; ventral margin with 3 bristles in proximal and distal groups; end joint with 3 claws and 4 bristles. All joints of mandible except end joint with clusters of surface spines. Number of dorsal and ventral bristles on mandibular basales of five specimens from type-locality is as follows:
Specimen
Left Mandible
Left Mandible
Right Mandible
Right Mandible
Dorsal
Ventral
Dorsal
Ventral
USNM 126219
7
3
7
3
USNM 126221
7
3
1
2
USNM 126222
7
3
7
3
USNM 127276
6
3
6
3
USNM 127490
6
3
6
3
Right mandible on USNM 126221: Mandibles of USNM 126219, USNM 126222, and left mandible of USNM 126221 same; right mandible of latter specimen with joint proportions normal but otherwise aberrant. Coxale endite consisting of single prong. Basale: dorsal margin with 1 bristle near middle, none terminally, proximal medial bristles not present; ventral margin with 2 distal bristles; lateral surface with 4 bristles oriented venteriad. Exopodite about 50 percent length of dorsal margin of 1st endopodite joint and with 1 bristle. Endopodite: 1st joint with 1 ventral bristle; dorsal margin of 2nd joint with 1 bristle; base of bristle proximal to middle; ventral margin with 2 bristles; 3rd joint with 4 bristles ar^l 1 claw.
Maxilla: Dorsal margin of precoxale and coxale with epipodial fringe; endite I with 10 bristles, endite II with 4, and endite III with 1 proximal and 10 distal bristles; anterior coxale bristle stout, spinous; anterior basale bristle short, bare; remaining 2 basale bristles long, spinous. Exopodite with 3 bristles: 1 short with short marginal spines; outer anterior bristle long with medium length marginal spines becoming progressively shorter distally on bristle; inner bristle long with wreaths of long spines proximally and short spines distally. Endopodite: anteromedial surface of 1st joint spinous; a-bristle long with wreaths of marginal spines proximally, no short marginal spines observed distally; 5 6-bristles present, all except 1 with few stout marginal spines; end joint with 3 a-bristles 2 b-bristles, 3 c-bristles and 3 d-bristles; 1 b-bristle and 2 d-bristles clawlike.
Fifth limb: Epipodial appendage with about 54 bristles; 3 endites present of usual type for genus. Exopodite 1st joint: anterior side with 2 bristles in middle of distal margin and 1 stout and 2 small faint bristles near lateral corner; 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, distal node bifurcate consisting of blunt distal process and pointed proximal process; posterior side of lateral corner of triangular tooth with fairly large spinous bristle (in other members of subfamily this bristle, when present, is minute and bare); anterior side of joint with long stout proximal bristle (pectinate near tip), and usual group of 3 bristles distal to basis of stout bristle. Exopodite 3rd joint: medial lobe with 3 bristles, all dentate or spinose; lateral lobe with 2 bristles with long proximal and short distal spines. Fourth and 5th joints with surface hairs and 6 spinous bristles.
Sixth limb: Epipodial appendage with 3 bristles with long proximal and short distal marginal spines; 1st endite with 2 or 3 bristles, 1 medial and 1 or 2 terminal; 2nd endite with 4 or 5 bristles, 1 medial, 3 or 4 terminal; 3rd endite with 8 or 9 bristles, 1 medial, 7 or 8 terminal; 4th endite with 8 or 9 bristles, 1 medial, 7 or 8 terminal; end joint with 23 bristles; all bristles on limb with marginal hairs or spines; long hairs present on medial and lateral surfaces of end joint. The distribution of bristles on endites of three specimens is listed below:
Endites
Endites
Endites
Endites
I
II
III
IV
USNM 126219
Left limb
2
4
9
8
Right limb
3
4
9
9
USNM 127490
Left limb
3
5
8
9
Right limb
Fragment
4
8
9
USNM 127493
Left limb
3
4
8
9
Right limb
3
4
9
9
Seventh limb: Each limb with 9 to 12 bristles, 5 in distal group and 4 to 7 distributed along limb proximal to distal group; each bristle with 3-5 bells and distal marginal spines; end comb with 13 to 15 teeth, middle tooth longer than others and recurved; all teeth alate; 2 or 3 small blunt pegs present opposite comb. The number and distribution of bristles on six specimens are as follows (A and B are opposing limbs):
A
A
A
B
B
B
Proximal
Distal
Total
Proximal
Distal
Total
USNM 126219
6
5
11
Appendage lost
-
-
USNM 126221
7
5
12
6
5
11
USNM 126222
4
5
9
6
5
11
USNM 127276
5
5
10
7
5
12
USNM 127490
5
5
10
5
5
10
USNM 127493
6
5
11
6
5
11
Furca: 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; medial row of marginal teeth of claw 1 larger than lateral row and with larger teeth near middle; proximal 4 or 5 bristles with spines along both margins; long hairs present on lamellae at bases of distal 4 or 5 claws and following last claw.
Eyes and rod-shaped organ: Lateral eye small with 2 or 3 ommatidia; medial eye large, pigmented, bare; rod-shaped organ elongated, 2-jointed, with rounded tip.
Upper lip: Lip hirsute with several spines near tip; rounded process present between lip and base of 1st antenna.
Posterior: Posterior margin and area hirsute.
Eggs: USNM 126219 and USNM 126221 with 4 eggs in marsupium; USNM 127493 with 16 eggs.
DESCRIPTION OF MALE—Carapace more elongate than that of female; angle formed between inferior margin of rostrum and anterior margin of carapace below rostrum obtuse, not acute as on female; small protuberance present on anterior margin near inferior corner of rostrum.
Infold: Infold broad along anterior and posterior parts of shell, narrow ventrally; infold on rostrum with 4 bristles along ventral margin, and 13 or 14 bristles paralleling anterior margin; 1 minute bristle present on infold below rostrum; about 12 bristles present in row on anteroventral infold; infold of caudal process with about 29 bristles forming row on or near list and 4 to 6 scattered bristles between list and posterior shell margin; 4 or 5 bristles present along posterior margin of infold of caudal process.
Selvage: Similar to that on female.
Ornamentation: Unlike female carapace, that of male strongly punctate; faint reticulations visible in transmitted light, especially on caudal process; bristles present along anterior, ventral, posterior margins, and scattered over valve surface.
Size: USNM 126220, length 1.94 mm, height 1.08 mm; USNM 126223, length 2.03 mm, height 1.19 mm; USNM 127258, length 1.75 mm, height 1.26 mm; USNM 127494, length 2.07 mm, height 1.16 mm.
First antenna: 1st joint bare; 2nd joint with spines forming clusters on medial surface and along ventral margin, and with 3 bristles: ventral bristle with long proximal and short distal spines; dorsal bristle with short marginal spines, lateral bristle reaching middle of 3rd joint. Third joint short, with 3 bristles, 1 ventral, 2 dorsal, and short spines forming clusters on medial surface; 4th joint with clusters of spines forming clusters on medial surface and 5 bristles, 4 ventral, 1 dorsal; sensory bristle of 5th joint with numerous filaments on broadened proximal part and 5 filaments forming tip; 6th joint with spinous medial bristle and few small spines forming clusters on medial surface. Seventh joint: a-bristle short spinous; b-bristle with 3 proximal and 4 terminal filaments; c-bristle very long with 13 marginal filaments (tip of bristle broken). Eighth joint: d- and e-bristle bare, similar in length, longer than b-bristle; f-bristle very long with 11 marginal filaments; g-bristle with 3 proximal and 4 terminal filaments.
Second antenna: Protopodite bare. Endopodite 3-jointed: 1st joint with 5 proximal bristles and 1 distal bristle; 2nd joint elongate with 3 ventral bristles near middle, proximal bristle more slender than remaining bristles; 3rd joint elongate, reflexed on 2nd joint, with 1 proximal bristle and 2 short subterminal bristles. Exopodite: 1st joint with short medial spine; bristle on 2nd joint with 8 ventral spines near middle; 9th joint with 4 long and 2 short bristles; bristles of joints 3 to 9 with natatory hairs; joints 2 to 8 with comb of short spines along distal margin; joints 3 to 8 with small basal spine.
Mandible: Coxale endite small with small adjacent bristle. Basale: medial surface with 5 or 6 short proximal bristles near ventral margin (2 pectinate, 3 or 4 spinous); proximal lateral surface and ventral margin with 4 spinous bristles; distal ventral margin with 2 or 3 (usually 3) spinous bristles; dorsal margin with 3 or 4 (usually 4) short bristles near middle and 2 terminal. Exopodite about 57 percent length of dorsal margin of 1st exopodite joint, with 2 terminal bristles, both with short marginal spines. Endopodite: 1st joint with 3 or 4 (usually 4) spinous ventral bristles; dorsal margin of 2nd joint with spinous bristles in 2 groups, proximal group with 3 bristles, distal group near middle of margin with 6 bristles; ventral margin with spinous bristles in 2 groups, each with 3 bristles; end joint with 3 claws and 4 bristles, all claws with minute teeth along ventral margins, medial and lateral claws also with teeth along middle of dorsal margin, lateral claw longer than medial claw, medial claw longer than dorsal claw. Medial surfaces of basale and 1st and 2nd joints of endopodite with spines forming clusters.
Maxilla and 5th limb: Both appendages reduced, epipodial appendage of 5th limb with 47 bristles.
Sixth limb: 1st and 2nd endites with 3 spinous bristles; 3rd and 4th endites with I proximal and 8 terminal bristles; end joint with 16 bristles, 7 plumose, remaining with long proximal and short distal spines; 3 short bristles present in place of epipodial appendage; short spines forming clusters present on lateral surface of end joint, long hairs on medial surface.
Seventh limb: 5 to 7 bristles in proximal group; 5 bristles in distal group; each bristle with 3 or 4 bells, some bristles with faint marginal spines distally; terminal comb with 9 to II alate teeth, middle tooth longer than others and curved; 2 small pegs present opposite comb.
Furca: Each lamella with 9 or 10 claws decreasing in length posteriorly along lamella; all claws separated from lamella by sutures; hairs present at bases of claws 1 to 5 and following last claw.
Eyes and rod-shaped organ: Lateral eyes large with about 23 ommatidia. Medial eye only slightly smaller than lateral eye, pigmented. Rod-shaped organ 2-jointed with rounded tip.
Upper lip: Lip elongate anteriorly with faint spines at tip.
Copulatory organ: Elongate reaching to base of 1st claw of furca.
Posterior: Posterior margin hirsute.
SEXUAL DIMORPHISM—In addition to usual differences, 1st joint of endopodite of 2nd antenna of male has 6 bristles compared to 7 on female, dorsal margin of the mandibular basale of male bears only 5 or 6 (usually 6) compared to 6 or 7 (usually 7) on that of the female, and end joint of 6th limb bears 16 bristles compared to 23 on female.
Community structure: The sample from station 0009 contained 50 adult males, 57 adult females, and 481 juveniles. Four eggs were present in 2 of the adult females; remaining females were without eggs. Many adult females were observed with broken bristles on the exopodites of their 2nd antennae.
COMPARISONS—This species is closely related to a specimen from McMurdo sound designated by Kornicker (1971) as Philomedes species A. That specimen is slightly larger than those from the Weddell Sea. Despite this and other minor differences Philomedes species A is placed herein in the synonymy of P. heptathrix, but with a question mark. The large number of bristles on both the endopodite of the 2nd antenna and the dorsal margin of the mandibular basale, combined with the presence of only 2 or 3 terminal pegs opposite the comb on the 7th limb, permits easy separation of P. heptathrix from previously described species of Philomedes.
DISTRIBUTION—This species was collected only in the Weddell Sea and in the vicinity of the Ross Sea, primarily at shelf depths." (Kornicker 1975, p.248-255)
