Comprehensive Description

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Description

"Thaumatoconcha, new genus

 

 

TYPE-SPECIES—Thaumatoconcha radiata, new species.

 

 

ETYMOLOGY—Name derived from a combination of the Greek thauma (wonder, marvel) + konche (shell).

 

 

This genus contains 8 species, all new and one additional taxon in open nomenclature: T. radiata, T. sandersi, T. hessleri, T. tuberculata, T. caraionae, T. elongata, T. polythrix, T. punctata, and Thaumatoconcha species A.

 

 

DISTRIBUTION—Atlantic Ocean, 32°N to 73°S; Pacific Ocean, 7°S to 70°S.

 

 

HABITAT—Benthic.

 

 

DIAGNOSIS—Carapace with ridges restricted to anteroventral surface of carapace; short anteroventral protuberances crudely reticulated; without posterodorsal tubercles except T. tuberculata; 1st antenna with 2 bristles on 1st joint; rod-shaped organ well developed. Surface smooth or coarsely to finely punctate, some species with small pustules visible with SEM; anteroventral surface with 1 to 11 thin ridges parallel to valve margin; cross-ridges on and near anteroventral protuberances; only 1species, T. tuberculata, with minute posterodorsal tubercule on right valve located posterior to similar tubercle on left valve. Dimensions of carapaces are compared in Figures 16, 17.

 

 

First antenna: 1st joint with 2 bristles, 1 dorsal, 1 lateral; 7th joint with 3 bristles, 2 ventral, 1 dorsal; 8th joint with 3 bristles.

 

 

Second antenna: First endopodial joint with 3 bristles, 1 ventral, 2 dorsal.

 

 

Fifth limb: 2nd exopodial joint without terminal bristle on ventral margin; 3rd exopodial joint with 2 (rarely 3) bristles.

 

 

Sixth limb: Process on dorsal corner of 1st exopodial joint with 3 bristles; 4th exopodial joint with 2 bristles.

 

 

Rod-shaped organ: Elongate with rounded or pointed tip.

 

 

DESCRIPTION OF APPENDAGES OF ADULT FEMALE—

 

 

First antenna: First joint with 1 dorsal and 1 lateral bristle; 2nd joint with 1 dorsal and 1 ventral bristle; 3rd and 4th joints fused except at sclerotized dorsal and ventral margins, especially the former; segment of dorsal margin of 3rd joint longer than that of 4th joint except for T. hessleri and Thaumatoconcha species A; 3rd and 4th joints usually without bristles, but rarely with a ventral bristle; 5th joint with 2 or 3 ventral bristles; 7th joint with 3 bristles, 2 -ventral, 1 dorsal; 8th joint with 3 bristles.

 

 

Second antenna: Protopodite without bristles. Endopodite 3-jointed: 1st joint with 3 bristles, 1 ventral, 2 dorsal; 2nd joint with 5 bristles, 1 ventral, 4 terminal; 3rd joint with 2 or 3 bristles. Exopodite with 8 joints, except T. radiata, T. punctata, and T. tuberculata which have 9: 1st joint divided into long proximal and short distal parts, without medial bristle; joints 2 to 8 with natatory bristles; 9th joint with 2 bristles, except T. radiata which has either 2 or 3.

 

 

Mandible: Proximal flat tooth of distal set on coxale endite with 1 large lateral cusp and 6 or 7 small pointed cusps. Basale: anterior margin of endite with 1 bristle; posterior margin with 3, rarely 2, proximal bristles, and usual blunt distal bristle; lateral side with flat knife-like process and 5, rarely 4, bristles. Endopodite: dorsal margin of 1st joint with 1 bristle, except T. polythrix which has 5 or 6 bristles; ventral margin of 2nd joint with 3 or 4 bristles; dorsal margin of 2nd joint with 2 bristles, except T. polythrix which has 3 bristles; 3rd joint with 6 or 7 bristles: 3 lateral (middle of these clawlike and longer than others), 3 or 4 medial (1 of these on or near ventral margin).

 

 

Maxilla: Endite I with 9-12 bristles; endite II with 8-11 bristles; endite III with 6-8 bristles. Basale with 2 bristles, 1 ventral, 1 dorsal. Endopodite: anterior margin of 1st joint with 5 or 6 bristles, except T. polythrix which has 7; posterior margin with 2 or 3 bristles; 2nd joint with 8 or 9 bristles, 1 of these is stout and claw-like, another, with base on posterior margin, is long and stout with short marginal spines.

 

 

Fifth limb: Epipodial appendage with 14 bristles arranged in 3 groups—5, 5, and 4. Protopodite and endopodite with 15-23 bristles. Exopodite: dorsal margin of 1st joint with usual single bristle; ventral margin of 1st joint with 6-10 bristles; ventral margin of 2nd joint with 2 or 3 midbristles; 3rd joint with 1 long claw-like bristle and 1 shorter bristle.

 

 

Sixth limb: Epipodial appendage with 15 plumose bristles; protopodite with 4 bristles, except T. polythrix which has 5 or more. Exopodite: process on dorsal corner of 1st joint with 3 bristles; 1st joint with 3-6 additional bristles, except T. polythrix which may have as many as 8; 4th joint with 1 long claw-like bristle and 1 shorter bristle.

 

 

Seventh limb: Small with 2 long spinous 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 claws.

 

 

Rod-shaped organ: Elongate, 1-jointed or weakly 2-jointed with tapered or rounded tip.

 

 

Posterior of body: Single process present proximal to furcal lamellae; posterior margin distinctly divided into narrow segments.

 

 

Lips: Upper lip: proximal part with triangular sclerotized lateral process on each side oriented anteriorly; distal part with 4 spine-like processes at tip oriented posteriorly; T. punctata with additional small processes on distal part of lip.

 

 

DESCRIPTION OF ADULT MALE—Similar in shape and ornamentation to that of female but slightly smaller.

 

 

First antenna: Joints 1, 2, and 3 similar to those of female, except 3rd and 4th joints separated by well-defined suture on some species (T. radiata, T. elongata, T. polythrix, T. sandersi); 4th joint with 2 ventral bristles; 5th joint with 3 ventral bristles, the longer of these with short marginal hairs (sensory bristle); 6th to 8th joints similar to those of female.

 

 

Second antenna: Protopodite and exopodite similar to those of female. Endopodite: 1st and 2nd joints similar to those of female; 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.

 

 

Mandible, maxilla, 5th limb, 6th limb, 7th limb, furca, rod-shaped organ, posterior, lips: Similar to those of female, but with few differences in numbers of bristles on mandible, 5th and 6th limbs that could be attributed to interspecific variability. An exception might be the 1st joint of the exopodite of the 6th limb of T. polythrix with 5 or 6 bristles compared to 8 on female.

 

 

Copulatory organ: Single organ consisting of 2 parts present on left side of body: anterior part elongate with either a recurved process, T. sandersi, a single long tooth-like process, T. caraionae, T. elongate, T. polythrix, a long tooth-like process with a minute tooth at its base, T. tuberculata, or about 8 teeth, T. radiata; posterior part shorter than anterior part, tapered, styliform with 3 hair-like bristles at tip.

 

 

COMPARISONS—See Table 13.

 

 

SHELL STRUCTURE—An outer layer of shell flaked off many specimens during the freeze-drying process used prior to SEM micrography. We observed that when the outer layer of shell is present, details of the central muscle attachment scar are not visible in reflected light or in SEM micrographs when the shell is viewed from the outside. The scar is visible when the outer layer has flaked off. Hemispherical nodules similar to those described by Sohn and Kornicker (1969:101) from Vargula hilgendorfii (Müller, 1890) were observed on a few carapaces of Thaumatoconcha radiata." (Kornicker & Sohn 1976, p.35-40)

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Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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