Metavargula adinothrix Kornicker 1975

"HOLOTYPE — USNM 125825, female, length 5.22 mm. Valves and some appendages in alcohol, remaining appendages on slides.

TYPE-LOCALITY—Eltanin Cruise 7, station 480, Atlantic Quadrant, Antarctica.

ETYMOLOGY—The specific name “adinothrix,” from the Greek “adinos” [= thick, dense, crowded] and “thrix” [= hair], refers to the abundance of bristles on the 7^th limb and in place of the epipodial appendage of the 6^th limb.

PARATYPES—USNM 125829, adult, female; USNM 125831, stage III instar, length 2.95 mm, height 1.69 mm; USNM 125974, 15 specimens, mostly juveniles; USNM 126120, 1 juvenile, length 4.31 mm, height 2.26 mm; USNM 126121, 1 juvenile, length 4.49 mm, height 2.57 mm. USNM 125829, 125831, 125974, 126120 from Eltanin Cruise 6,.station 350; USNM 126121 from Eltanin Cruise 27, station 1980.

ADDITIONAL SPECIMENS—USNM 138141, 1 juvenile (not dissected), length 3.72 mm, height 1.99 mm, + 1 juvenile with only small part of shell, both from Eltanin Cruise 6, station 394; USNM 137469, ovigerous female dissected by N. Hidings, his number 233, appendages missing, valves and upper lip present, right valve length 6.31 mm, height 3.96 mm, from Vema Cruise 17, station V- 17-63.

DIAGNOSIS—Carapace length of adult female, 5.22-6.31 mm.

Sixth limb: 10 small bristles in place of epipodial appendage.

Seventh limb: Each limb with about 54 bristles.

Furca: Each lamella with 8 claws.

DESCRIPTION OF FEMALE—Carapace with broadly rounded anterior and fairly deep incisor; posterior with elongate upsweeping caudal siphon.

Ornamentation: Surface smooth but scalelike under high magnification.

Infold: Infold broad in area of rostrum and caudal process, narrower elsewhere; infold behind rostrum with about 24 bristles; infold behind incisur with 1 small bristle; infold of anteroventral and ventral margin with 16 short bristles followed by 7 to 10 minute bristles or pores and then about 20 short bristles; list on infold in front of caudal process with about 34 small processes and about 10 minute bristles; vestment in area of caudal process with reticulate structure.

Selvage: Wide lamellar prolongation with smooth outer margin present along anterior and ventral margins, being quite broad in area of incisur; prolongation striate along lower margin of incisur and anteroventral valve margin.

Central muscle scars: Scars indistinct but consisting of 16 to 19 individual scars; in 1 juvenile specimen in process of molting individual scars are arranged in a series of inverted chevrons.

Size: USNM 125825, length 5.22 mm, height 3.08 mm; USNM 125829, length 5.91 mm, height 3.37 mm; USNM 137469, right valve, length 6.31 mm, height 3.96 mm.

First antenna: 3^rd and 4^th joints each with ventral and dorsal bristle; sensory bristle of 5^th joint with 9 long proximal filaments and 2 shorter distal filaments, tip bifurcate; bristle of 6^th joint bare, about one and one-half times length of joint. Seventh joint: a-bristle bare, slightly longer than bristle of 6^th joint; b-bristle with 4 short filaments; c-bristle with 9 filaments. Eighth joint: d- and e-bristles about half length of c-bristle and about one and three-quarters length of b-bristle; f- and g-bristles broken but with at least 9 filaments; proximal filaments of g-bristle with few marginal teeth.

Second antenna: Protopodite with short bare medial bristle. Endopodite weakly 2-jointed: 1^st joint with 3 bare proximal bristles, 1 long and 2 short, and 1 long distal bristle with few spines; 2^nd joint short with long terminal filament. Exopodite: bristle of 2^nd joint with about 17 minute spines along ventral margin and about 7 proximal spines along dorsal margin, bifurcate tip reaching 9^th joint; bristles on joints 3 to 9 with natatory hairs and without spines; 9^th joint with 4 bristles, 3 long, 1 short; joints 3 to 8 with short spines forming row along distal margins; joints 3 to 9 with basal spines; basal spines smaller on proximal joints, but lateral spine on 9^th joint smaller than basal spine of 8^th joint.

Mandible: Coxale endite spinous with 2 terminal spines stouter than others and with short peg between them; short process and bristle present at base of endite. Basale: dorsal margin with 1 distal bristle with few marginal spines and 2 terminal bristles, both with short marginal spines; ventral margin with 2 a-bristles with bases on medial side, 1 very short, 1 b-bristle with base on lateral surface, 2 c-bristles (1 long spinous proximal, other short bare) and 2 d-bristles. Exopodite slightly longer than dorsal margin of 1^st exopodite joint and with 2 spinous bristles, tip of exopodite hirsute. Endopodite: ventral margin of 1^st joint with 4 bristles, 2 long spinous, 2 short bare; ventral margin of 2^nd joint spinous, with 3 groups of bristles having 1, 1, and 2 bristles, all short; medial bristle of terminal pair broad and with teeth along inner margin; dorsal margin of 2^nd joint with about 6 long and 10 short bristles; end joint with 4 claws (one of these more bristlelike than others) and 3 bristles.

Maxilla: Coxale with stout plumose bristle. Exopodite broad with usual 3 bristles, all with long marginal spines proximally. Endopodite: cutting edge of 1^st endopodite joint with 3 large teeth; 2 a-bristles present, outer bristle spinous, inner shorter bristle bare; 3 6-bristles present with spines along inner margin; 2^nd joint with 4 a-bristles consisting of 2 slender bare inner bristles and 2 longer outer bristles with a few proximal marginal spines; 3 b-bristles present, middle bristle bare, others with spines on inner margin; 4 c-bristles present, short bristle bare, others with marginal spines; 3 d-bristles present, 2 inner bristles nonannulate and bare, outer bristle annulate and with marginal spines.

Fifth limb: Epipodial appendage with 64 hirsute bristles; distoanterior process of protopodite small; 1^st endite with 6 spinous bristles, 2^nd endite with 5 large spinous bristles and 1 small bare posterior bristle; 3^rd endite with 7 spinous bristles; main tooth of 1^st endopodite joint consisting of usual 6 pectinate teeth and peg with proximal posterior bristle; anterior side of 1^st joint with 4 bristles, 2 long, 2 short, all with marginal spines; 2^nd endopodite joint with plumose anterior bristle and numerous bristles on margin adjacent to main tooth of 1^st joint; inner lobe of 3^rd joint with 3 bristles, shorter bristle spinous, other 2 with only 1 or 2 spines; outer lobe with 2 spinous bristles; 4^th plus 5^th joints united with small spined peg at border; 4^th joint with 4 bristles, 5^th with 2; posterior surfaces of endopodite joints 2 to 5 hirsute.

Left 6^th limb: 10 small bare bristles in place of epipodial appendage; 1^st endite with 4 bristles, 3 medial, 1 terminal; 2^nd endite with 6 bristles, 4 medial, 2 terminal; 3^rd and 4^th endites each with 3 terminal bristles; medial bristles of endites with slender marginal hairs; terminal bristle of 1^st endite with long marginal spines; terminal bristles of remaining endites with fronds of long spines proximally and short spines distally; end joint with 19 bristles, 2 posterior bristles hirsute, others with long proximal spines and short distal spines; medial surface of endites and end joint hirsute; ventral margin of end joint with lateral spines except in space between 4 posterior bristles and 15 anterior bristles.

Right 6^th limb: 2^nd endite with 8 bristles, 5 medial, 3 terminal; 4^th endite with 4 bristles, 1 medial, 3 terminal; end joint with 18 bristles. In remaining characters, right limb same as left.

Seventh limb: Distal group with 27 bristles, 15 ventral, 12 dorsal, each with 3 to 6 bells; proximal group with 24 bristles, 11 ventral, 13 dorsal, each with 3 to 6 bells; terminal comb with 11 elongate recurved teeth with marginal spines; elongate incurved peg present opposite comb; teeth and peg annulate.

Furca: Each lamella with 8 claws separated from lamella by suture; claws decrease in length posteriorly along lamella, each claw with teeth along posterior margin.

Upper lip: Anterior part large, unpaired and with crenulate margin; 1 pair of posterior tusks present; bulge posterior to tusks hirsute.

Lateral eye: Eyes small, pigmented, each with 3 or 4 ommatidia.

Medial eye and rod-shaped organ: Medial eye large, pigmented along midline. Rod-shaped organ short, cylindrical.

Genitalia and brushlike organ: Genitalia with pustulose surface and attached cuplike structures (spermatophores?). Brushlike cluster of 7 or more minute annulate bristles present dorsal to genitalia.

Eggs: USNM 137469 with 28 eggs.

Parasites: USNM 125829 contained within its shell, attached to the body in the area of the lateral right eye, a female copepod (Choniostomatidae). USNM 125825 contained within its shell, attached to the posterodorsal part of the body, 2 isopod larvae. USNM 126120 also contained an isopod, either a larva or an adult male. Remaining specimens without parasites.

DESCRIPTION OF JUVENILE— It is similar to that on the adult female.

COMPARISONS—This species is larger than other members of the genus and has many more bristles both on the 7^th limb and in place of the epipodial appendage of the 6^th limb.

DISTRIBUTION—This species has been collected from Antarctic, Subantarctic, and Subantarctic-to-35°S regions (lat. 48°S to 59°S) at bathyal and abyssal depths (1796-3775 m)." (Kornicker 1975, p.131-138)