"Thaumatoconcha radiata, new species FIGURES 3-8,10b, 11l, 12j, 18d-f; 19-23; 24a-i; 25-34
HOLOTYPE—USNM 143794, adult female, some appendages on slides, carapace and some appendages in alcohol.
TYPE-LOCALITY—USCGC Glacier station 0022, 73°29'S, 30°24'6"W, Weddell Sea, 3035 m.
PARATYPES—USNM 126136, 74 specimens; USNM 127272A, B, 2 specimens; USNM 143753, ca. 1200 specimens; USNM 143754A-C, 49 specimens; USNM 126139, 1 juvenile; USNM 143858, 12 specimens; USNM 143799, 176 specimens. USNM 126136 and 126139 from type-locality.
OTHER LOCALITIES—USNM 127272 from USNS Eltanin, Cruise 4, station 127, 61°45'S, 61° 14’W, Drake Passage, 4758 m; USNM 143753 from R. V. Atlantis II, Cruise 60, station 245A, 36°55'42"S, 53°01'24"W, South Atlantic, 2707 m; USNM 143754 from R. V. Atlantis II, Cruise 60, station 259, 37°13'18"S, 52°45'00"W, South Atlantic, 3305- 3317 m; USNM 143858A-D from R. V. Vema Cruise 14, station V-14-25 (Lamont Geological Observatory station 49) 56°43'S, 27°41'W, 2747 m; USNM 143799 from R. V. Atlantis II, Cruise 60, station 262A, 36°05'12"S, 52°17'54"W, South Atlantic, 2440-2480 m.
ETYMOLOGY—The specific name radiata is in reference to the radial structure of the adductor muscle attachments.
DIAGNOSIS—Surface smooth with 4 or 5 anteroventral ridges and straight anteroventral margin; dorsal margin of 3rd joint of 1st antenna longer than dorsal margin of 4th joint; endopodite of mandible with 1 dorsal bristle on 1st joint and 2 on 2nd joint; rod-shaped organ with rounded tip; tip of male copulatory organ with long straight tooth and with numerous short teeth.
DESCRIPTION OF ADULT FEMALE—Valves subround, height of anterior margin greater than posterior; straight anteroventral margin delimited by a dorsal and a ventral forward pointing, short, truncated pro-tuberance; anterodorsal margin broadly convex, merging with short straight dorsal margin at point about one-third greatest length; posterior margin evenly rounded; ventral margin curving gently forward and downward to point approximately below subcentral adductor musclescar, then curving upward to join anteroventral margin below protuberance. Dorsal outline subelliptical, greatest width in front of midlength; end outline subelliptical, greatest width slightly below midheight.
Ornamentation: Surface smooth; widely spaced pore-canals with hairs that branch distally observed near anterior margin; anteroventral surface with 4 thin ridges parallel to valve margin (some individuals have a discontinuous 5th ridge); upper protuberance located between the 2 ridges closest to the contact margin, in form of truncated pentagonal pyramid with 5 thin ridges forming corners; ridge on posterior corner perpendicular to contact margin; remaining 4 ridges each join one of the 2 ridges closest to contact margin; cross-ridges form crude reticulations around protuberance; lower protuberance located between 2nd and 4th thin ridges, covered with irregular reticulations formed by cross-ridges and capped by a rimmed pore containing a single hair; 2 of the thin ridges extend along ventral margin, of these, ridge closest to contact margin continues to hinge margin, other terminates at posteroventral margin.
Adductor muscle attachment scar: Scar subcentrally located in area of greatest width; subround, greatest diameter trending towards posterior end of hinge; scar consists of from 19 to 24 subequal wedged-shaped segments more-or-less radially arranged.
Size: USNM 143794 (holotype), left valve, length 1.90 mm, height 1.63 mm; right valve, length 1.88 mm, height 1.67 mm. USNM 126136Y, left valve, length 1.94 mm, height 1.69 mm; right valve, length 1.94 mm, height 1.72 mm. USNM 126136Z, complete specimen, length 2.02 mm, height 1.61 mm; USNM 126136G, complete specimen, length 1.97 mm, height 1.71 mm; USNM 126136H, complete specimen, length 1.98 mm, height 1.71 mm. USNM 143753A, left valve only, length 1.72 mm, height 1.50 mm; USNM 143753E, left valve only, length 1.72 mm, height 1.49 mm; USNM 143753N, left valve only, length 1.79 mm, height 1.58 mm; USNM 143753P, complete specimen, length 1.83 mm, height 1.60 mm; USNM 143753R, complete specimen, length 1.85 mm, height 1.59 mm; USNM 143753W, right valve only, length 1.66 mm, height 1.49 mm; USNM 143753KK, disarticulated valves, left valve, length 1.77 mm, height 1.50 mm; right valve, length 1.76 mm, height 1.46 mm; USNM 143753XX, right valve only, length 1.76 mm, height 1.60 mm. USNM 143754A, complete specimen, length 1.88 mm, height 1.70 mm. USNM 143858A, length 2.03 mm, height 1.74 mm; USNM 143858B, length 2.13 mm, height 1.83 mm. USNM 143799A, complete specimen, length 1.84 mm, height 1.66 mm.
First antenna: Limb with 8 joints: 1st joint with minute spines on lateral surface (near distal margin), numerous long spines on medial surface, 1 dorsal bristle with short marginal spines, and 1 spinous lateral bristle on small protuberance; 2nd joint with 1 ventral bristle reaching to or beyond 8th joint and 1 dorsal bristle reaching 5th to 8th joints, both bristles with short marginal spines; 3rd and 4th joints fused except in sclerotized areas on ventral and dorsal margins; 3rd joint distinctly longer than 4th joint; 3rd joint with long spines on ventral and dorsal margins and on medial surface (rarely with ventral bristle); 4th joint with few short marginal spines and rarely with minute terminal bristle on ventral margin; 5th joint with few short spines on dorsal margin and with 3 terminal ventral bristles, 1 short (not always present), and 2 long with widely separated short marginal spines; 6th joint with few spines along dorsal margin; 7th joint with 1 short ringed dorsal bristle with short marginal spines and 2 terminal ventral bristles with widely separated short marginal spines; 8th joint with 1 short terminal dorsal bristle with short marginal spines, and 2 long terminal bristles with widely separated short marginal spines.
Second antenna: Protopodite with long hairs forming clusters along ventral margin; lateral surface with numerous blunt spines on arcuate sclerite proximal to base of endopodite. Endopodite weakly 3-jointed: 1st joint with medial spines, 1 ventral and 2 dorsal bristles, both with short marginal spines; 2nd joint narrower and longer than 1st joint, with medial spines along ventral margin and on medial surface, 1 lateral bristle with short marginal spines, and 4 terminal bristles on ventral half of distal margin, all with widely separated short marginal spines; 3rd joint with 3 terminal bristles (rarely 2 or 4): 1 short, ventral, with closely spaced short marginal spines, and 2 longer, with more widely spaced marginal spines; suture separating 3rd and 4th joints present only on medial side. Exopodite 9-jointed (rarely with 8): 1st joint with suture dividing it into long proximal and short distal parts, with spines along ventral margin and forming row along terminal margin; joints 2—8 each with 1 long bristle with natatory hairs and short spines along ventral margin (number of bristles with spines varies); 9th joint with 3 (only 2 on some specimens) bristles, 1 long and 1 medium with natatory hairs, 1 short with short marginal spines (when short bristle is absent, medium bristle bears only spines); joints without basal spines but with some distal hairs.
Mandible: Coxale endite with proximal and distal sets of teeth separated by small space; proximal set consisting of 4 broad teeth plus rounded tooth near space; about 3 clusters of very densely packed spines present medially between each tooth (bases of cluster extending onto medial surface of endite); 1 ointed or blunt spinous bristle present in space between proximal and distal sets of teeth; distal set of teeth consisting of 2 flat teeth; proximal flat tooth consisting of 1 large lateral cusp and 6 or 7 small pointed medial cusps; distal flat tooth with 6 pointed cusps (cusp 2 counting from lateral side onger than others); 1 spinous bristle present on lateral side of base of proximal flat tooth and about half length of adjacent cusp; medial and lateral surfaces of endite with short spines forming clusters on distal part near teeth. Basale: teeth of endite with 5 triangular cusps with minute serrations along margins; posterior margin of endite with single proximal bristle and distal blunt bristle with minute short tube-like process at tip (process visible at X 1000); anterior margin of endite with 1 bristle; lateral side of endite hirsute with 4 or 5 spinous bristles varying in location on different specimens, and short triangular process with minute teeth on lateral side near anterior margin; medial side of basale with cluster of long hairs near outer edge and mound with 1 long outer bristle with very long proximal hairs and short distal spines, and 1 long inner bristle with short spines. Endopodite 3-jointed with 1st and 2nd joints about same length and 3rd joint shorter; 1st joint with 1 spinous dorsal bristle and spines forming clusters on lateral and medial surfaces and along ventral margin; ventral margin of 2nd joint with 3 or 4 spinous bristles (2 or 3 near middle, 1 terminal); dorsal margin of 2nd joint with 2 claw-like bristles, both with marginal spines (distal bristle slightly broader at base than proximal bristle); terminal end of 3rd joint with 3 lateral spinous bristles (middle of these claw-like and about twice length of others) and 4 medial spinous bristles (1 of these on or near ventral margin).
Maxilla: Endite I with ca. 11 bristles; endite II with 9-11 bristles; endite III with ca. 7 bristles; some endite bristles broad, flat, pectinate. Basale with long dorsal bristle with long proximal and short distal spines; ventral margin of basale with long bristle with short marginal spines (this bristle may be on 1st endopodite joint). Endopodite: 1st joint hirsute, with 5 or 6 slender spinous bristles on anterior (dorsal) margin, 2 terminal spinous bristles and 1 short subterminal bristle on posterior (ventral) margin, and 1 short proximal spinous bristle with base on medial surface; anterior edge of terminal margin of end joint with 1 stout claw-like bristle with minute blunt teeth along middle of anterior edge, and short spines along middle of posterior edge; terminal margin of end joint with 7 slender bristles, and 1 long stout posterior bristle with short marginal spines; anterior margin of joint with short spines.
Fifth limb: Epipodial appendage with bristles in 3 groups, each with 5, 5, and 4 plumose bristles. Protopodite and endopodite with total of 23 bristles; distal endopodite joint with short triangular tooth-like process. Exopodite 3-jointed: 1st joint with 1 long spinous terminal bristle near dorsal margin, and 7 bristles near ventral margin; 2nd joint hirsute, slender, longer than 1st, with 3 midbristles near or on ventral margin; end joint with 1 short spinous bristle, and 1 long claw-like bristle with spines along ventral margin.
Sixth limb: Epipodial appendage with ca. 15 plumose bristles; protopodite hirsute, unjointed, with 4 bristles near or on ventral margin. Exopodite 4-jointed: 1st joint divided by weak suture into proximal part with 2 spinous ventral bristles, and short distal part with 2 spinous bristles on ventral edge of terminal margin (some variation noted on number and distribution of bristles); small process with 3 plumose bristles present on dorsal corner of terminal margin of 1st joint; 2nd and 3rd joints hirsute, completely fused, with 3 ventral and 1 dorsal bristles, all with long marginal spines; end joint with 1 slender bristle with short marginal spines, and 1 terminal claw-like bristle with short spines along ventral margin.
Seventh limb: Small, tapered, with 2 long spinous terminal bristles.
Furca: Each lamella with 2 long anterior claws separated by suture from lamella followed by 6 short claws joined to lamella; 1 small process oriented posteriorly present following other claws; lamellae with spines forming rows; each claw with teeth along anterior and posterior margins.
Rod-shaped organ: Elongate, 1-jointed or weakly 2-jointed with rounded tip, reaching just beyond terminal margin of 1st joint of 1st antenna.
Posterior of body: Single process with minute marginal spines present proximal to furcal lamellae; posterior margin distinctly divided into narrow segments; segmentation becoming less distinct anteriorly.
Lips: Upper lip projecting posteriorly and with 2 short stout outer processes and 2 narrower inner pointed processes which may have glandular opening at tip. Lower lip consisting of 2 triangular flaps, each with sclerotized pointed process at tip.
FOOD—USNM 143753KK with fragments of appendages of myodocopid ostracodes and possibly other crustacea in gut.
DESCRIPTION OF ADULT MALE—Similar in shape and ornamentation to that of female but slightly smaller.
Size: USNM 143753C, left valve only, length 1.69 mm, height 1.40 mm; USNM 143753V, left valve only, length 1.66 mm, height 1.39 mm; USNM 143753AA, left valve only, length 1.64 mm, height 1.46 mm. USNM 143753JJ, disarticulated valves: left valve, length 1.61 mm, height 1.35 mm; right valve length 1.64 mm, height 1.40 mm. USNM 127272A disarticulated valves, right valve, length 1.99 mm, height 1.74 mm; left valve, length 1.97 mm, height 1.73 mm. USNM 143754B, complete specimen, length 1.77 mm, height 1.53 mm. USNM 143858D, complete specimen, length 1.91 mm, height 1.67 mm. USNM 143799B, complete specimen, length 1.72 mm, height 1.54 mm.
First antenna: Limb with 8 distinct joints; 1st joint similar to those of adult female; 2nd joint with 1 ventral bristle reaching beyond 8th joint and 1 dorsal bristle reaching to about middle of 4th joint, both bristles with short marginal spines; 3rd joint spinous, much smaller than 2nd; 4th joint smaller than 3rd and with 2 long bare ventral bristles; 5th joint short, with 3 ventral bristles (longest of these with curved hairs along ventral margin, others bare); 6th joint without bristles; 7th joint with 2 long bare ventral bristles and 1 short spinous dorsal bristle; 8th joint with 2 long bare bristles and 1 short spinous bristle.
Second antenna: Protopodite and exopodite similar to those of adult female. Endopodite: 1st and 2nd joints similar to those of adult female; 2nd joint weakly separated from 3rd; 3rd joint with large curved sclerotized hook-like process with 2 minute spines at tip; surface of hook pustulose near tip; base of process either on medial side of joint or terminal. (Length and curvature of hook-like process varies among specimens of the same species and between the left and right appendages of the same specimen.)
Mandible, maxilla, 5th limb, 6th limb, 7th limb, furca, rod-shaped organ, posterior of body; lips: Similar to those appendages on adult female, but with a few differences in number of bristles on mandible, maxilla, 5th and 6th limbs.
Copulatory organ: Single organ present on left side of animal consisting of 2 parts: anterior part elongate with ca. 8 teeth at tip; posterior part about one-half length of anterior part, tapered, styliform with 3 hair-like bristles at tip.
DESCRIPTION OF FEMALE A-l INSTAR—Carapace similar in shape to that of adult female.
Size: USNM 143753F, right valve only, length 1.56 mm, height 1.35 mm; USNM 143753DD, complete specimen, length 1.56 mm, height 1.37.
First antenna: Limb with 8 joints: 1st joint with long hairs on medial surface and 1 dorsal and 1 lateral bristle similar to those on adult female; 2nd joint with 1 ventral bristle reaching to distal end of 6th joint and 1 dorsal bristle reaching to middle of 5th or 6th joints, both bristles with short marginal spines; 3rd joint with long spines on ventral and dorsal margins and medial surface; 3rd and 4th joints fused; 4th joint with few clusters of marginal spines on ventral and dorsal margins and minute terminal ventral bristle (right limb of USNM 143753F also with 2 terminal broad, flat, transparent bristles); 3rd joint distinctly longer than 4th joint; 5th joint with few short spines along dorsal margin and 3 terminal ventral bristles (1 short inner bristle on lateral side; 2 long outer bristles with widely separated short marginal spines); 6th joint with few clusters of short spines on lateral and medial sides near dorsal margin; 7th and 8th joints similar to those on adult female.
Second antenna: Similar to that of female adult except 3rd joint of endopodite with 5 bristles, 3 short, 2 medium; terminal joint of exopodite with 2 bristles, 1 long with ventral spines and natatory hairs, 1 medium with only spines.
Mandible, maxilla, 5th, 6th and 7th limbs, posterior of body, and upper lip: General morphology similar to that of adult female.
Furca: Similar to that of adult female except with only 5 short claws.
Rod-shaped organ: Elongate, 1-jointed or weakly 2-jointed; USNM 143753DD with rounded tip similar to that on adult female; USNM 143753F with tapered tip, unusual for this species.
DESCRIPTION OF MALE A-l INSTAR—Carapace similar in shape to that of A-l female.
Size: USNM 143753CC, complete specimen, length 1.55 mm, height 1.33 mm. USNM 143753MM, disarticulated specimen, right valve broken; left valve, length 1.50 mm, height 1.27 mm. USNM 127272B, complete specimen, length 1.74 mm, height 1.52 mm.
First antenna: Similar to limb of A-l female with following exceptions: ventral margin of 4th joint with 2 fairly long terminal bristles with broad proximal part and 1 minute inner bristle (the latter bristle not present on all limbs); ventral margin of 5th joint with 2 long bristles, 1 short bristle, and 1 minute inner bristle (the latter bristle not present on all limbs).
Second antenna: Similar to limb on A-l female with following exceptions: 3rd joint of endopodite thumb-like with 5 (rarely 4) short terminal bristles.
Mandible, maxilla, 5th, 6th, and 7th limbs, posterior of body, upper lip: General morphology similar to that of adult female.
Furca: Similar to that of A-l female.
Rod-shaped organ: Elongate, 1-jointed with rounded tip.
Copulatory organ: Shorter than that on adult; anterior part with about 3 minute teeth at tip; posterior part about one-half length anterior part, not tapered or styliform like that on adult, with 3 small bristles at tip.
DESCRIPTION OF ATYPICALLY DEVELOPED MALE A-l INSTAR—Carapace similar in shape to normal A-l male.
Size: USNM 143753Y, left valve only, length 1.47 mm, height 1.28 mm.
First antenna: Similar to that on normal A-l male with following exceptions: ventral margin of 4th joint with 2 short terminal bristles; ventral margin of 5th joint with 3 terminal bristles.
Second antenna: Similar to that on female A-l instar except shape of 3rd joint on endopodite approaching that of male A-l instar.
Mandible, maxilla, 5th, 6th, and 7th limbs, posterior of body, upper lip: General morphology similar to that of adult female.
Furca: Similar to that of A-l female.
Rod-shaped organ: Bifurcate (abnormality), ventral organ longer and narrower than dorsal organ and with rounded tip; dorsal organ with tapered tip and minute terminal process; both organs with few spines on surface.
Copulatory organ: Smaller than that on normal A-l instar; anterior lobe with 1 long spine or bristle and ca. 4 minute teeth; posterior lobe with 3 bristles somewhat longer than those on normal A-l instar.
Remarks: This specimen, although having a carapace similar in size to other A-l instars, bears an endopodite on the 2nd antenna and a copulatory organ that seem to be in degree of development between the A-l and A-2 instars.
DESCRIPTION OF FEMALE A-2 INSTAR—Carapace similar in shape to that of adult female.
Size: USNM 126136B, left valve only, length 1.34 mm, height 1.19 mm. USNM 143753H, right valve only, length 1.29 mm, height 1.12 mm; USNM 143753BB, right valve only, length 1.29 mm, height 1.17 mm. USNM 143753OO, complete specimen, length 1.24 mm, height 1.12 mm. USNM 143753PP, disarticulated valves: right valve, length 1.27 mm, height 1.12 mm; left valve, length 1.30 mm, height 1.13 mm.
First antenna: Similar to that on A-l female with following exceptions: ventral bristle on 2nd joint shorter than dorsal bristle; ventral margin of 4th joint with 1 or 2 short terminal bristles or with 1 short bristle and 1 longer bristle reaching past 5th joint; ventral margin of 7th joint with 1 long bristle, 1 medium length bristle, and 1 minute bristle (latter bristle not always present).
Second antenna: Similar to that on female A-l instar except inner bristle on 2nd joint of endopodite very short and 3rd joint with 4 or 5 bristles.
Mandible, maxilla, 5th, 6th, and 7th limbs, posterior of body, upper lip: General morphology similar to that of adult female.
Furca: Similar to that of A-l female except with only 4 short claws.
Rod-shaped organ: Elongate, 1-jointed with rounded tip.
DESCRIPTION OF MALE A-2 INSTAR—Carapace similar in shape to that of A-2 female.
Size: USNM 126136A, disarticulated valves, right valve, length 1.35 mm, height 1.15 mm; left valve, length 1.37 mm, height 1.15 mm. USNM 1261361, complete specimen, length 1.26 mm, height 1.14 mm. USNM 143753K, complete specimen, length 1.21 mm, height 1.09 mm; USNM 143753X, complete specimen, length 1.28 mm, height 1.11 mm.
First antenna: Same as that on A-2 female except ventral margin of 4th joint with 2 bristles: 1 lateral bristle almost reaching or just reaching beyond distal margin of 5th joint; 1 medial bristle about half length lateral bristle. (The female A-2 instar USNM 126136B has bristles on the 4th joint similar to those on the male A-l instars examined.)
Second antenna: Similar to that on A-2 female except 3rd joint of endopodite thumb-like (thumb less well defined than that on A-l male).
Mandible, maxilla, 5th, 6th, and 7th limbs, posterior of body, upper lip: General morphology similar to that of adult female.
Furca: Similar to that of A-2 female.
Rod-shaped organ: Elongate, 1-jointed. USNM 126136A, 143753X, 143753K with tapered tip, the latter with minute process at tip; USNM 1261361 with rounded tip.
Copulatory organ: With long anterior lobe with 1 spine-like tooth and shorter posterior lobe with 1 short terminal bristle.
DESCRIPTION OF A-3 INSTAR—No sexual dimorphism observed. Carapace similar in shape to that of A-2 instars.
Size: USNM 143753L, complete specimen, length 1.10 mm, height 0.93 mm; USNM 143753Z, left valve only, length 1.03 mm, height 0.91 mm; USNM 143753FF, complete specimen, length 1.09 mm, height 0.92 mm; USNM 143753II, disarticulated valves: right valve, length 1.10 mm, height 0.97 mm; left valve, length 1.11 mm, height 0.96 mm; USNM 143753NN, complete specimen, length 1.12 mm, height 0.98 mm.
First antenna: Similar to that of female A-2 instar with following exceptions: lateral bristle of 1st joint shorter than dorsal bristle; 2nd joint without ventral bristle; ventral margin of 4th joint with 1 or 2 minute bristles, or 1 minute bristle and 1 longer bristle almost reaching distal margin of 5th joint; ventral margin of 5th joint with 2 bristles, 1 long, 1 short (about same length as 5th joint); ventral margin of 7th joint with 1 long terminal bristle, 1 short bristle about twice length of 8th joint, and 1 minute bristle (the minute bristle or both the minute and short bristle not always present).
Second antenna: Similar to that on female A-l instar with following exceptions: Endopodite: 1st joint with 1 dorsal bristle; 2nd joint without lateral bristle and with 3 terminal bristles on ventral half of distal margin; 3rd joint with 4 bristles. Exopodite: 9th joint minute and not distinctly separated from 8th joint.
Mandible, maxilla, 5th, 6th, and 7th limbs, posterior of body, upper lip: General morphology similar to that of adult female.
Furca: Similar to that of A-2 female except with only 3 short claws.
Rod-shaped organ: Elongate, 1-jointed with slightly or distinctly tapered tip.
Copulatory organ: Not developed.
DESCRIPTION OF A-4 INSTAR—No sexual dimorphism observed. Carapace similar in shape to that of A-3 instar.
Size: USNM 143753M, complete specimen, length 1.00 mm, height 0.87 mm; USNM 143753U, left valve only, length 0.94 mm, height 0.81 mm; USNM 143753HH, complete specimen, length 0.94 mm, height 0.82 mm; USNM 143753RR, disarticulate valves: right valve, length 0.93 mm, height 0.81 mm; left valve, length 0.95 mm, height 0.82 mm.
First antenna: Similar to that of A-3 instar with following exceptions: 1st joint without lateral bristle; ventral margin of 4th joint without bristles; 5th joint with 1 long ventral bristle, ventral margin of 7th joint with 1 long and 1 very short bristle.
Second antenna: Similar to that on A-3 instar with following exceptions: Endopodite: no dorsal bristle present on 1st joint; 2 terminal bristles on 2nd joint (inner of these very short); medioventral bristle on terminal margin of 3rd joint very short. Exopodite: 1st joint not divided into 2 parts; 8th and 9th joints fused, with 2 bristles, 1 long with natatory hairs and marginal spines, the other medium with only marginal spines (the natatory bristle is considered here to be on the 8th joint and the spined bristle on the 9th).
Mandible, maxilla, 5th limb, posterior of body, upper lip: General morphology similar to that of adult female.
Sixth limb: Reduced but with many bristles.
Seventh limb: Absent.
Furca: Similar to that of A-3 female except with only 2 short claws.
Rod-shaped organ: Elongate, 1-jointed with rounded or tapered tip.
DESCRIPTION OF A-5 INSTAR—No sexual dimorphism observed. Carapace similar in shape to that of A—4 instar; 4th thin ridge on anteroventral surface discontinuous.
Size: USNM 143753G, complete specimen, length 0.80 mm, height 0.62 mm; USNM 1437531, complete specimen, length 0.82 mm, height 0.73 mm; USNM 143753EE, complete specimen, length 0.80 mm, height 0.71 mm, USNM 143753GG, complete specimen, length 0.85 mm, height 0.71 mm. USNM 143753QQ, disarticulated valves: right valve, length 0.79 mm, height 0.69 mm, left valve, length 0.80 mm, height 0.69 mm.
First antenna: Similar to that of A-A instar with following exceptions: 2nd joint without bristles; ventral margin of 7th joint with 1 long bristle; 8th joint with 2 bristles, 1 medium, 1 long.
Second antenna: Similar to that of A-4 instar except 2nd endopodite joint with only 1 long bristle. (Remarks: USNM 143753G was in process of molting.)
Mandible, maxilla, 5th limb, posterior of body, upper lip: General morphology similar to that of adult female.
Sixth limb: Rudimentary without bristles.
Seventh limb: Absent.
Furca: Similar to that of A—4 female except with only 1 short claw.
Rod-shaped organ: Elongate, 1-jointed with round or tapered tip, some with a minute terminal process.
DESCRIPTION OF A-6 INSTAR—No sexual dimorphism observed. Carapace similar in shape to that of A-5 instar; only 3 ridges on anteroventral surface.
Size: USNM 143753B, right valve only, length 0.71 mm, height 0.60 mm; USNM 143753D, complete specimen, length 0.69 mm, height 0.59 mm; USNM 143753J, left valve only, length 0.67 mm, height 0.56 mm; USNM 143753O, complete specimen, length 0.67 mm, height 0.58 mm; USNM 143753Q, right valve only, length 0.70 mm, height 0.60 mm; USNM 143753S, complete specimen, length 0.73 mm, height 0.58 mm. USNM 143753LL, disarticulated valves: right valve, length 0.71 mm. height 0.61 mm; left valve, length 0.68 mm, height 0.60 mm. USNM 143753SS, complete specimen, length 0.67 mm. height 0.59 mm.
First antenna: Similar to that of A-5 instar except without bristles on 1st joint.
Second antenna: Similar to that of A-5 instar except no bristles on the 1st endopodite joint.
Mandible, maxilla, 5th limb, posterior of body, upper lip: General morphology similar to that of adult female.
Sixth and seventh limbs: Absent.
Furca: Similar to that of A-3 female except without well-developed short claws, and claw 2 not separated from lamella by suture.
Rod-shaped organ: Elongate, 1-jointed with tapered or irregular tip.
Ontogeny: Summarized on p. 7.
“NUMBER OF GROWTH STAGES—Thirty-seven specimens, including representatives of all size classes, were removed from 1200 specimens of Thaumatoconcha radiata, new species, in a single sample (R.V. Atlantis II Cruise 60, station 245A). The selected specimens were measured and then dissected. The appearance of appendages and the spacing of clusters of the various sizes of carapaces plotted on a length-height graph indicate that the sample contained 6 juvenile instars in addition to male and female adults of this species. Examination of all collections containing all the species of Thaumatoconcha did not produce any specimens whose carapace size or developmental stage indicated an A-7 growth stage in the genus. Growth factors are shown on Tables 2 and 3. The carapace length of the smallest specimens of T. radiata in the sample from station 245A varied from 0.67 to 0.73 mm, and the height from 0.56 to 0.60 mm. According to Mrs. Susan P. Garner, Woods Hole Oceanographic Institution (letter of 23 July 1973), this sample is from the residue retained on a 0.297 mm screen. Using the growth factor calculated for this species, an A-7 growth stage, if present, would have been retained on the screen. The sample is from a depth of 2707 m, considered to be a low energy, stable environment. Reproduction is assumed to be nonseasonal, and migration negligible. Therefore, we conclude that the 7 stages represent the complete ontogeny of T. radiata and, most likely, the other species in the genus.
The furca of living thaumatocyprids bears 2 long anterior claws followed by short claws. Except for Danielopolina orghidani (Danielopol, 1972), the furca of adults bears 6 short claws, and the number of short claws is decreased by one in each previous growth stage (Table 1). Thus, the number of short claws on each lamella of the furca is diagnostic of the growth stages in living species of the Thaumatocyprididae. The furca of the adult D. orghidani, a cave form, bears only 4 short claws; the number of short claws on the furcae of its juvenile is unknown.
DEVELOPMENT OF GROWTH STAGES—The earliest juvenile, the A-6 instar, does not have the 6th and 7th limbs; this is discussed under the description of Thaumatoconcha radiata. The 6th limb of the A-5 instar is a small bare lobe; this limb has many bristles on the A-4 instar. The 7th limb appears on the A-3 instar. The copulatory limb of the male appears on the A-2 instar. The male cannot be recognized in earlier instars. Investigation of juveniles selected at random from other species of Thaumatoconcha indicates that the order of appearance and general development of limbs conform to those of T. radiata.
In general, the morphology of the carapace of the instars is similar to that of the adult. It was not possible to differentiate males and females in A-6 to A-3 instars. The average growth factor of the shell excluding the growth factor between the preadult and adult male is 1.17. This estimated factor was obtained by averaging both the length and height factors between male and female instars. The growth factor between the preadult and adult male is quite low, 1.08 for both length and height growth factors.
ORDER OF APPEARANCE OF APPENDAGES—The A-6 instar bears a rod-shaped organ, 1st and 2nd antennae, mandibles, maxillae, and 5th limbs. The 6th limb appears as a small lobe without bristles (anlage) on the A-5 instar (this was observed on at least 1 side of specimens examined, but was not always observed on both sides of the same specimen). The 6th limb has many bristles on the A-4 instars. The 7th limb appears on the A-3 instar. The copulatory limb of the male appears on the A-2 instar.
First antenna: This limb contains 8 joints in instars A-6 to A-l and on adults, but only on the adult male is the 4th joint separated from the 3rd by a distinct suture. The 3rd and 6th joints are without bristles in both instars and adults. Remaining joints have fewer bristles in early instars than in late instars and adults. An exception is the 4th joints on female appendages, which have no bristles on instars A-6 to A-4 (sex undifferentiated), at least 1 bristle on instars A-3 to A-l, and may have no bristles on the adult (some adults have 1 bristle). The 2 bristles on the 4th joint of the male appendage are much longer on adults than on instars A-l and A-2. The male A-l instars have 4 bristles on the 5th joint of some specimens, whereas the adults have only 3, but this may be the result of intraspecific variability. The presence of more bristles on the 7th joints of A-2 and A-3 instars than on adults may also be attributed to intraspecific variability.
Second antenna: Exopodite: The 8th and 9th joints are fused on instars A-6 to A-4 and are separated by a suture on instars A-3 to adults. The fused 8th and 9th joints on instars A-6 to A-4 bear 1 bristle; the 9th joints on instars A-3 to A-l bear 2 bristles, and the 9th joints on adults bear 3. Endopodite: 3 joints are present on all instars and on adults. Fewer bristles are present on joints 1 and 2 of early instars than on later instars and adults, but the full accompaniment of bristles is reached on instar A-2. The 3rd joint is unusual in that the adult appendage bears fewer bristles than that of the A—1 instar. This is especially noticeable in the male, because the adult bears on the 3rd joint a hook-like process which might represent a bristle, but could also be an extension of the joint.
Mandible, maxilla, fifth limb: General morphology on all juvenile instars similar to that of the adult female.
Sixth limb: This limb first appears in instar A-5 as a lobe without bristles. It is small, but with numerous bristles on the A-4 instar, and is fully developed on the A-3 instar to adult.
Seventh limb: This limb first appears in the A-3 instar and has 2 bristles like on the adult.
Furca: The claws of the furca may be divided into long anterior claws, short middle claws, and a posterior process. Instars A-6 to adults bear 2 long anterior claws and 1 posterior process. The number of short middle claws increases from 0 on the A-6 instar to 6 on the adult. One short claw is added in each instar.
Rod-shaped organ: This organ is 1-jointed or weakly 2-jointed in instars A-6 to adults. The tip is evenly rounded on adults; however, both rounded and tapered tips were observed on instars.
Posterior of body, lips: General morphology similar to that on adults.
Male copulatory appendage: The A-2 instar is the earliest stage on which the copulatory appendage was observed. The anterior lobe bears 1 spine-like terminal tooth on the A-2 instar, 3 or 4 minute teeth on the A-l instar, and about 8 larger teeth on the adult. The posterior lobe is sausage-shaped in the A-2 and A-l instars and styliform on the adult. The tip of the process bears 1 bristle on instar A-2, 3 bristles on instar A-l, and 3 hairs on the adult.” (Kornicker & Sohn 1976, p.7-16)
COMPARISONS—See Table 13." (Kornicker & Sohn 1976, p.40-58)
