"Philomedes trithrix, new species
Figs. 6-12
Holotype. USNM 125200, gravid female, length 2.61 mm, height 1.97 mm. Valves and some appendages in alcohol, remaining appendages on slides.
Paratypes from Arthur Harbor, Anvers Island. USNM125201 gravid female, Station 3, July 14, 1967; USNM 125202, female without eggs, Station 2, June 20, 1967; without eggs (returned to Mr. James K. Lowry), Station 2, June 20, 1967; USNM 125203, USNM 125204, adult males, Station 2, May 17, 1967; USNM 125208, female without eggs, Station 2, July 15, 1967; USNM 125209-125212, 4 juveniles from Station 2, female July 15, 1967; USNM 125213-125215, 3 juveniles from Station 3, February 20, 1967.
Paratypes from off Greenwich Island. USNM 125390, adult female, Station 45; USNM 125391, adult female, Station 47; USNM 125392, adult female, Station 37; USNM 125393, adult female, 10 eggs in brood chamber, Station 55; USNM 125394, juvenile male, Station 47; USNM 123395, adult female, 5 eggs in brood chamber, Station 42; USNM 125396, adult female with eggs in brood chamber (not dissected), Station 58. In addition, 182 specimens were returned to Tomas Cekalovic K., Curador del Museo, Departamento de Zoologia, In-stituto Central de Biologia, Universidad de Concepcion, Concepción, Chile.
Paratype from Melchior Harbor. USNM 125493, adult female , Stations 32-63.
Type locality. Arthur Harbor, Anvers Island, Station 3.
Other localities. Arthur Harbor, Anvers Island, Station 2; Greenwich Island vicinity, Stations 21, 22, 23, 24, 25, 26, 27, 29, 31, 32, 34, 35, 37, 41, 42, 43, 44, 45, 47, 48, 51, 52, 54, 55, 56, 58, 60, 61; USS Staten Island, Stations 32-63, Melchior Harbor, off Gamma Island.
Etymology. The specific name `trithrix,' from the Greek `tri,' three, and `thrix,' hair, refers to the three bristles on the second joint of the endopodite of the female second antenna.
Distribution. The number of specimens collected at each station is as follows: Arthur Harbor, Station 2 (numeral following date is number of specimens): May 17, 1967-2; June 20, 1967-2; July 15, 1967‑5. Arthur Harbor Station 3: February. 20, 1967-3; July 14, 1967-2. Greenwich Island vicinity (numbers are station and number of specimens): 21-4, 22-5, 23-3, 24-3, 25-9, 26-6, 27-6, 29-1, 31-5, 32-1, 34-4, 35-2, 37-8, 41-6, 42-11, 43-2, 44-4, 45-1, 47-7, 48-3, 51-2, 52-5, 54-3, 55-22, 56-26, 58-36, 60-1, 61-3. One specimen was collected in Melchior Harbor, off Gamma Island, USS Staten Island Stations 32-63. Specimens were collected at depths ranging from 33 meters to 355 meters and on bottoms consisting of sand, fine sand, sandy mud, silts, and mud. In Arthur Harbor, the temperature ranged from -1.7°C to 0°C, and the salinity was normally 34 parts per thousand.
Description of female. Carapace oval in lateral view with greatest height near middle; broad rostrum overlapping large wide incisur; each valve with small caudal process not always showing in lateral view.
Ornamentation: Surface with faint pits, numerous small spinelike hairs, and few scattered very long hairs.
Infold: Infold of rostrum with 14-18 long, spinous bristles paralleling anterior margin and 3-4 bristles paralleling ventral margin; infold posterior to incisur with short bristle; anteroventral part of infold striate and with about 16 spinous bristles; caudal process with 2-4 bristles along outer edge and 3-5 bristles at middle of infold; infold along posterior and ventral margins with numerous minute bristles along inner margin.
Selvage: Striate lamella prolongation with fringed edge consisting of long and short spines present on all except hinge margins of each valve.
Muscle scars: Central muscle scars not clearly visible laterally.
Size: USNM 125200, gravid female, length 2.61 mm, height 1.97 mm; USNM 125201, gravid female, length 2.59 mm; height 1.99 mm; USNM 125202, adult female, length 2.65 mm, height 2.00 mm; adult female, length 2.58 mm, height 1.90 mm; USNM 125208, female without eggs, length 2.50 mm, height 1.91 mm; USNM 125390, adult female, eggs within body, bristles of second antennae broken, length 2.33 mm, height 1.77 mm; USNM 125391, adult female, eggs within body, bristles of second antennae broken, length 2.46 mm, height 1.81 Irma; USNM 125393, gravid female, 10 eggs in brood chamber, length 2.59 mm, height 1.91 mm; USNM 125493, female without eggs, length 2.48 mm, height 1.79 mm. Range: length 2.33-2.65 mm; height 1.77-2.00 mm.
First antenna: First and second joint with spines in clusters on medial and lateral surfaces; second joint with ventral, dorsal, and lateral bristle, all with wreaths of long spines; third joint with 1 ventral and 2 dorsal spinous bristles; fourth joint with 4 spinous bristles, 3 ventral, 1 dorsal; bristle on fifth joint with 4 proximal and 4 terminal filaments; bristle on sixth, joint with wreath of long spines and short spines distally; a-bristle spinous; b-bristle with 1 proximal filament and 4 terminal filaments; c-bristle with 5 proximal and 4 terminal filaments; d- and e-bristles bare and of equal length; f- and g-bristles with 3 proximal and 4 terminal bristles.
Second antenna: Endopodite 2-jointed: First joint with 5 bristles, 4 in proximal group, 1 distal; second joint elongate with proximal, distal, and terminal bristle: proximal bristle 2 to 2½ times length of joint, with numerous long spines along middle part and short spines distally; distal bristle about half length of proximal bristle, with few long spines near middle and short spines distally; terminal spine usually recurved, bare; short spines forming few small clusters on joint surface. Exopodite: First joint with small terminal medial spine; joints 2 to 8 with minute spines forming clusters along distal margin; bristle of second joint extends well past ninth joint; ninth joint with 6 bristles, 4 long, 1 medium and 1 short; bristles on joints 6 to 8 and 4 long bristles on ninth joint broken; medium and short bristle of ninth joint with spines, all remaining bristles without spines and natatory hairs.
Two gravid females (USNM 125200, USNM 125201) and 1 adult female without eggs (USNM 125202) from Anvers Island and others from Greenwich Island stations are as described above. One adult female without eggs (USNM 125208) differs from the above description in having the long bristles of the exopodite unbroken. The long bristles on joints 6 to 9 are about 3 times the length of bristles on joints 2 to 5 and have natatory hairs.
Mandible: Coxale endite large, bifurcate, with short, triangular teeth and long, thin spines; small bristle present at basis of endite; basale with 6 medial-proximal bristles: 3 with wreaths of long hairs, 3 with stout marginal teeth; 4 spinous bristles forming row on lateral surface paralleling ventral margin (proximal bristle of the 4 is on ventral margin on some specimens); 3 distal bristles present on ventral margin; dorsal margin of basale with 2 terminal bristles and 2 bristles distal to middle, all bristles with long spines; long spines forming clusters on medial and lateral surface of coxale and basale; exopodite about 80% length of first endopodite joint and bearing 2 bristles longer than exopodite; first endopodite joint with 5 ventral spines; dorsal margin of second endopodite joint with 3 groups of bristles: with proximal group with 2-4 bristles, middle group 1 bristle, distal group with 6 bristles; ventral margin with 2 groups of bristles: proximal group with 4 bristles, distal group with 3 bristles; medial surface of joint with spines forming clusters; end joint with 3 bare claws and 4 bristles.
Maxilla: Normal for genus; first endopodite joint with 1 alpha- and 4 beta-bristles, all with marginal spines.
Fifth limb: Epipodial appendage with 58 bristles; first endite with 6 bristles; main tooth lowed first exopodite joint with large, square tooth fol- lowed by 2 teeth with serrate edge and small spinelike tooth; triangular, smooth protuberance present an- terior to main tooth; small bristle present on posterior side near outer corner of large tooth of second endopiodite joint; posterior side of second joint with usual 4 bristles; third endopodite joint with usual 3 inner bristles and 2 outer bristles, both outer bristles with long marginal spines; fourth and fifth joints hirsute, with 7 spinous bristles.
Sixth lamb: Epipodial appendage with 3 spinous bristles; first endite with 3 spinous bristles, 2 short, 1 long; second endite with 4 spinous bristles, proximal 3 terminal; third and fourth endite each with 9 spinous bristles, 1 proximal, 8 terminal; end joint with 27-28 spinous bristles; lateral and medial surfaces of end joint hirsute.
Seventh lamb: Each limb with total of 36-43 bristles, each with 3-8 bells and a few short marginal spines distally; terminal comb with 9-15 curved teeth having lateral wings and 1 or 2 small teeth on each side at base; 7-12 pegs about 3½ times long as wide present opposite comb.
Furca: Distribution of claws normal for genus; 11 to 13 claws present; claws 7 to 10 or 13 with fine spines along anterior and posterior margins and could be considered secondary; claws 1–6 with teeth along concave margin; long spines forming medial clusters at base of claws.
Rod-shaped organ and medial eye: Medial eye well developed. Rod-shaped organ elongate, widening in middle, weakly 2-jointed on some specimens.
Lateral eye: Small with only 2 or 3 ommatophores.
Upper lip and anterior: Upper lip simple hirsute, projecting anteriorly. Single pointed projection present in the middle of anterior margin between upper lip and rod-shaped organ.
Eggs: 13 oval eggs in brood chamber of USNM 125200; 7 eggs in chamber of USNM 125201; 10 eggs in chamber of USNM 125393; 5 eggs in chamber of USNM 123395.
Epibiota: Many appendages with filamentous and stalked protistans.
Description of adult male: Carapace more elongate than female and with prominent caudal process; surface with few scattered long and short hairs; small pits, usually faint or absent on female, abundant on male; central muscle scars consisting of about 11 individual scars. Size: USNM 125203, length 2.53 mm, height 1.55 mm; USNM 125204, length 2.61 mm, height 1.55 mm.
First antenna: Second, third, fourth, sixth joints with clusters of spines on medial surface; second joint with 3 bristles: 1 ventral, 1 dorsal, 1 lateral; third joint with 1 ventral and 2 dorsal bristles; fourth joint with 2 spinous bristles: 3 ventral, 1 dorsal; sensory bristle of small fifth joint with many filaments on the broad proximal part and 4 terminally; sixth joint with short medial bristle; bristles of joints 7-8 typical for genus.
Second antenna: Endopodite 3-jointed: First joint with 5 bristles, 4 proximal and 1 distal; distal bristle about same length as proximal bristles; second joint with 3 spinous bristles; third joint with 1 proximal and 2 short subterminal bristles; ridges present at tip of third joint. Exopodite: bristle of second joint without marginal spines or natatory hairs; bristles of joints 3-8 with natatory hairs; ninth joint with 4 long and 1 short bristles, short bristle with few hairs, long bristles with many long hairs.
Mandible: Coxale endite small, bifurcate at tip, with short bristle at base. Basale: medial surface with clusters of spines and 6 bristles, 5 proximal and 1 near middle; ventral margin with 5 spinous bristles; dorsal margin with 4 bristles as on female. Exopodite about 60% length of first endopodite joint and bearing 2 bristles similar to female. Endopodite: First joint with clusters of spines on medial surface and 5 ventral spines; second joint with clusters of spines on medial surface; ventral margin of second joint with 3 bristles in proximal and distal groups; dorsal margin as in female; end joint as in female.
Maxilla, fifth limb: Reduced, typical for genus.
Sixth limb: Epipodial appendage with 3 plumose bristles; first endite with 3 bristles; second endite with 1 proximal and 3 distal bristles; third endite with 1 proximal and 8 terminal bristles; fourth endite with 1 proximal and 6 terminal bristles; end joint with 18 bristles; surface of endites 2-4 and end joint hirsute.
Seventh limb: Each limb with total of 29 to 31 bristles (1 specimen), each bristle with 2-4 bells; terminal comb with about 10 curved teeth; 3 pegs present opposite comb.
Furca: Each lamella with 9 to 10 claws.
Rod-shaped organ and medial eye: Similar to female.
Lateral eye: Large with about 20 divided ommatophores in lateral view.
Copulatory organ: Elongate but small, about two-thirds the length of claw 1 of furca.
Upper lip: Similar to that of female.
Description of ? male instar II.
Carapace: Similar in shape to adult male; size: USNM 125213, length 0.83 mm, height 0.58 mm.
First antenna: Third joint right limb with 2 bristles, 1 ventral, 1 dorsal; left limb with 3 bristles, 1 ventral, 2 dorsal; fourth joint with 1 dorsal and no ventral bristles.
Second antenna: Ninth joint of exopodite with 3 bristles; all exopodite bristles with short marginal teeth or spines.
Endopodite (2-jointed): First joint with 1 bristle; second joint with 1 spinous ventral bristle and 1 recurved terminal bristle.
Mandible: Dorsal margin of basale with 1 bristle near middle and 2 terminal.
Sixth limb: Bilobed with 1 bristle between lobes; both lobes with long marginal spines.
Seventh limb: Short, bare.
Furca: Each limb with 6 claws. Lateral eye small with 2 or 3 ommatophores.
Description of ? female instar III.
Carapace: Similar in shape and ornamentation to adult female, but with more prominent caudal process.
Size: USNM 125209, length 1.52 mm, height 1.22; USNM 125210, length 1.65 mm, height 1.22 mm.
First antenna: Fourth joint with 1 ventral and 1 dorsal bristle, number of bristles on remaining joints similar to adult female.
Second antenna: Ninth joint with 3-4 bristles, shortest of these with short spines, others bare; bristles of joints 2-8 bare; first joint with short medial spine.
Endopodite (weakly 3-jointed): First joint with 3 bristles; second joint with 2 ventral bristles; third joint with 1 coiled or recurved dorsal bristle and 1 short terminal bristle.
Fifth limb: Epipodial appendage with 39 bristles.
Sixth limb: Has numerous bristles.
Seventh limb: Long, bare.
Furca: Each lamella with 8 claws.
Medial eye: Similar to adult.
Rod-shaped organ: 1- or 2-jointed with 1 or 2 hairs at tip.
Description of ? male instar ? IV.
Carapace: Similar in shape to adult male.
Size: USNM 125214, length 1.52 mm, height 1.01 mm.
First antenna: Ventral margin of second joint with 2 bristles; fourth joint with 1 dorsal and 2 ventral bristles.
Second antenna: Endopodite: Similar to ? female instar III.
Mandible: Dorsal margin of basale with 4 bristles.
Sixth limb: Numerous bristles.
Seventh limb: 4 proximal and 4 distal tapering bristles.
Lateral eye: Small with about 3 ommatophores.
Furca: Each lamella with 8 claws.
Description of male instar ? V.
Carapace: Similar in shape to adult male.
Size: USNM 125215, length 1.84 mm, height 1.22 mm; USNM 125394, length 1.82 mm, height 1.15 mm.
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First antenna: Second joint with 2 ventral bristles and no dorsal bristles; fourth joint with 2 ventral and 1 dorsal bristles; number of bristles on other joint same as on adult female.
Second antenna: Endopodite (3-jointed): first joint with 4 short bristles; second joint with 1 long and 2 short ventral bristles; third joint with 1 long, recurved dorsal bristle and 2 short terminal bristles.
Exopodite: Bristles of joints 6-9 short and without natatory hairs.
Mandible: Dorsal margin of basale with 4 bristles as in adult.
Seventh limb: 9 tapering bristles, 5 in distal group and 4 in proximal group; terminus with comb of about 11 teeth opposing 2 pegs.
Furca: Each lamella with 9 claws.
Lateral eye: USNM 12515, similar to adult female; USNM 125394, similar to adult male but smaller.
Description of female instar ? V.
Carapace: Similar in shape and ornamentation to adult female.
Size: USNM 125211, length 1.87 mm, height 1.65 mm; USNM 125212, length 2.16 mm, height 1.63 mm.
First antenna: Fourth joint with 3 bristles, 2 ventral and 1 dorsal; number of bristles on remaining joints similar to adult female.
Second antenna: Ninth joint of exopodite with 5 bristles; bristles of joints 2-8 and long bristles of ninth joint bare; bristles of joints 6-9 relatively short. Endopodite (2-jointed):femalefemale joint with 4 bristles; second joint as on adult female.
Seventh limb: Each limb with 37-39 tapering bristles, each with 2-3 bells; terminal comb with about 13 teeth; 5-8 pegs present opposite comb.
Furca: Each lamella with 9-10 claws.
Development. An insufficient number of instars (8) were examined to do more than sketch the development of the species. The reproductive organs are not well developed in early instars, so they are not useful for determining the sex of specimens. In late stages the morphology of the endopodite of the second antenna is useful for determining sex, but in early stages it is not sufficiently known to be used with certainty. It was observed that in the N-1 stage the male and female could easily be distinguished by the lateral outline of the carapace, which resembles that of the adult; i.e., the female has a minute caudal process, whereas the male has a prolonged one. It was also observed that similar differences were present in the shape of carapaces of earlier instars whose sexes were unknown. The shape of the carapace was then used to identify the sex of the early instars. I am uncertain about the reliability of the method and therefore must consider the sex determinations of the earlier instars to be tentative. This is indicated by a ‘?’ before the sex indication. I presented a key [Kornicker, 1969a] for identifying instars I, II, and III; that key is used herein for identifying those stages.
Sexual dimorphism. The carapace of the male is more elongate than the female and has a more prominent caudal process, more distinct surface pits, and fewer short surface hairs. Sexual differences between the first and second antennae, mandible, maxilla, and fifth limb are of the usual type for the genus. The sixth limb of the male has fewer terminal bristles on the third and fourth endites and only 18 bristles on the end joint compared to 27-28 on the end joint of the female. The seventh limb of the male bears only 29-31 bristles and 3 terminal pegs, compared to 39-43 bristles and 7-12 terminal pegs in the female. The furca of the male bears 9-10 claws, compared to 11-13 in the female.
Remarks. Possibly the males described herein as P. trithrix are not conspecific with that species. The distinct pitting on the carapace of the male and the presence of only 3 pegs on the male seventh limb compared to 7-12 on the female are differences that suggest nonconspecificity. Males and females have been considered conspecific because of the following reasons: (1) The number of bristles on the seventh limbs of both sexes (29-31 on male, 39-43 on female) is higher than previously reported for species of the genus. (2) The dorsal margins of the basales of the mandibles of both the males and females have 4 bristles having similar positions on the margin. Not man species in the genus have precisely this number.
Comparisons. P. trithrix differs from P. charcoti in having more bristles on the seventh limb and in having more than 2 bristles on the second joint of the endopodite of the second antenna.
P. trithrix differs from P. rotunda Skogsberg, 1920, in having more bristles on the female seventh limb seventh limb (37-43 bristles compared to 23-26). The terminus of the seventh limb on the female of P. rotunda has only 3 Pegs compared to 7-12 for P. trithrix. The dorsal margin of the basale of the mandible of P. rotunda bears only 3 bristles compared to 4 on P. trithrix. The length of the female P. rotunda is 1.9-2.1 mm compared to 2.33-2.65 mm for P. trithrix. The carapace of P. trithrix has a small caudal process that is not present on P. rotunda.
In the key to species of Philomedes given by Poulsen [1962, p. 345] the present species would key out to Philomedes curvata Poulsen, 1962. P. trithrix differs from that species in having more bristles on the end joint of the sixth limb and also on the seventh limb. The female of P. trithrix has a lateral eye that is absent on P. curvata.
The carapace of the adult female of P. trithrix is similar to the carapace of P. orbicularis illustrated by Brady [1907, pl. 1, figs. 1, 2]; however, the appendages illustrated by Brady [pl. 1, figs. 8, 9, 11] do not resemble the appendages of P. trithrix. Possibly the appendages illustrated by Brady are not from P. orbicularis (see discussion herein under P. orbicularis). When P. orbicularis becomes better known, it may be necessary to place P. trithrix in its synonymy. " (Kornicker 1971, p. 176-185)
