Crosniera wennerae, Heard, Richard W. & King, Rachael A., 2007

Heard, Richard W. & King, Rachael A., 2007, Crosniera wennerae, a new species of thalassinidean (Crustacea: Decapoda: Thomassiniidae) from the South Atlantic Bight, Zootaxa 1644, pp. 41-49 : 42-46

Crosniera wennerae sp. nov.

Figures 1–3

Material examined. HOLOTYPE. USNM 174403, non-ovigerous female, total length 20 mm, off North Carolina, USA, 33°00.97'N, 77°20.20'W, 318 m, Texas Instruments/Minerals Management Service Station 1F, 10 February 1977.

Diagnosis. Female. Rostrum acute. Eyes poorly developed, each with two ommatidia and some pigment, lobes subacute distally. Maxilliped 2 and 3 each with well-developed exopod, extending beyond articulation of merus and carpus. Maxilliped 3 merus inner margin smooth. Telson without lateral spines. Uropodal margins smooth, endopod without spine on lateral margins.

Description. Female holotype.

Rostrum acutely tipped, not reaching beyond eyes. Carapace 6 mm in length, without mid-dorsal keel; linea thalassinica relatively short, extending posteriorly less than 1/3 length of carapace, vertical row of six setae in antennal region of anterior carapace, three outer-most setae longest and plumose; cervical groove barely evident. Abdominal segment 2 longer than all others, with medial and anterior ventrolateral margins lightly fringed with setae, posteroventral margin with dense cluster of setae; abdominal segments 3–5 each with cluster of setae near ventrolateral margin just past mid-length; segment 6 posterelateral margins each with cluster of three long, simple setae extending to mid-region of telson. Telson dorsal surface smooth with a pair of proximal shallow lobes on lateral margins, with 7–8 long simple dorsal setae at 1/3 length; posterior margin broadly rounded and fringed with plumose setae, with two groups of 3 long submarginal simple setae near each distolateral margin.

Eyestalks stout, with blunt tips, dorsally rounded and flattened ventrally; eyes each with two ommatidia and some defuse pigmentation. Antenna 1 damaged, inner flagellum missing; peduncle article 3 reaching slightly beyond distal margin of antenna 2 article 4; scaphocerite reduced to small scale. Antenna 2 damaged, first 4 articles present.

Upper lip sparsely setose. Mandible incisor process strongly dentate, with 7–8 irregular teeth; shallow molar process with 3 teeth (two on distal inner margin and one on mid-inner margin; palp broad, strongly developed, distal article length about equal to that of articles 1 and 2 combined, distal half densely setose, with mix of simple and setulate spiniform setae. Maxilla 1 proximal endite with inner margin armed with row of setulate or pectinate, spiniform setae some becoming longer and bearing bidentate tips on proximal half of endite; distal endite with inner margin bearing row of stout spiniform conical setae; exopod with two articles, cluster of four setae on proximal margin of article 2, article 2 with long (subequal to article 2) curved spini form seta. Maxilla 2 endopod not tapering, tip blunt, curved laterally, extending slightly past distal-most endite and anterior tip of scaphognathite; scaphognathite well-developed, posterior lobe with distinctive long, terminal seta extending well into branchial chamber. Maxilliped 1 exopod lacking articulated palp; endopod not extending past distal endite; distal endite with distal margin straight, widest distally; proximal endite weakly bilobed; epipod damaged, distal lobe missing, represented only by narrow proximal lobe. Maxilliped 2 endopod with merus about twice combined length of carpus, propodus, and dactylus; exopod uniarticulate, well-developed, setose, extending just beyond distal end of merus of endopod; epipod and small podobranch present, epipod with several hooked setae along margin of distal half, with cluster of long simple setae present proximally. Maxilliped 3 endopod setose, ischium about twice as long as wide, inner face with row of 10 spines (9 in distal half of article and 1 in proximal half); merus globular, longer than carpus, about equal in length to propodus; dactylus rounded distally, paddle-shape, less than twice as long as wide; exopod extending well past articulation of merus and carpus, with five articles, first article slightly longer than combined length of last four, distal article with two long, setulose terminal setae; epipod tapering distally, with two podobranchs present, proximal outer margin with numerous simple setae, tip armed with several hooked setae.

Gastric mill strongly developed; lateral ossicles with grinding processes lobate proximally becoming spiniform distally, first two processes lobate with rounded tips and having inner margins densely spinose; next two processes attenuate with dentate tips, with inner margins bearing six spines and a tridentate spine, tips of next few setae grading from bidentate to deeply bifurcate, distal most 3–4 setae simple with curved acute tips.

Pereopod 1 chelae dissimilar; right (major) chela more robust; its fixed finger bearing strong blunt subdistal tooth and small proximal tooth on cutting edge near articulation with movable finger; minor chela (left) fixed finger with single relatively small tooth midway along cutting edge. Pereopod 2 missing. Pereopod 3 with propodus about twice as long as wide, distal margin armed with single well-developed, spiniform seta. Pereopods 4, 5 and 6 missing.

Pleopod 1 uniramus, peduncle shorter than ramus, with cluster of seven long brush-tipped setae on outer distal margin; ramus with several small hooked setae along outer margin (similar to those on epipod of maxilliped 1), with 10 distal and subdistal plumose setae, presence of two apparently fused distal articles indicated. Pleopod 5 damaged, exopod missing, endopod about 3.5 times as long as wide, appendix interna with 15 small coupling hooks, with a row of 6 brushed-tipped setae on posterior face in between appendix interna and articulation with basal article.

Uropodal exopod length slightly more than 1.5 times width, broadly rounded, not bilobed, lateral margins fringed with plumose setae, short attenuated “cone setae” interspersed with fringing setae along outer mid-lateral margin, extending distally and merging with short, blunt tipped, spiniform setae, becoming less numerous medially; blunt spiniform setae extending nearly to inner distal margin; 3 or 4 long thin simple seta present on proximal lateral margin and 1 on subdistal margin; endopod length about 1.7 times width, with fringing row of plumose setae along distal half, with 2 long simple setae near proximal lateral margin and 7 or 8 long simple setae on subdistal and distal margin.

Branchial formula as in Table 1.

Etymology. This species is named for Elizabeth L. Wenner, of the South Carolina Department of Natural Resources, in recognition of her many contributions to crustacean biology and to the understanding of the ecology and faunal biodiversity of the South Atlantic Bight.

Table 1. Branchial formula for Crosniera wennerae . Epipod/podobranch on maxillipeds 2 and 3 (thoracomeres 2 & 3), epipods on thoracomers 4–7 (reduced or rudimentary [= r] on thoracomere 7). Single (1) arthrobranch on thoracomere 3, two (2) arthrobranchs on 4-7 becoming larger posteriorly.

Distribution and Habitat. Crosniera wennerae sp. nov. is presently known from only the type locality in soft substratum on the upper continental slope (318 m) in the northern part of the South Atlantic Bight.

Remarks. Crosniera wennerae sp. nov. appears to have closer affinities with the western Pacific C. corindon than with the type species, C. minima , the only other member of the genus currently known from the western Atlantic.

Crosniera wennerae sp. nov. and C. corindon both lack a spine on the lateral margin of the uropodal endopod, but differ in a variety of characters including the lengths of the exopods on maxillipeds 2 and 3 (much longer in C. wennerae sp. nov.) and the setation patterns on the carapace, uropods, and telson. C. wennerae sp. nov. is readily distinguished from C. minima by several characters including (1) the shape and dentition of the first chelipeds, (2) smooth margin of the uropodal endopod, (3) shape and setation of the uropods and telson. The following key distinguishes the nominal species of the genus Crosniera .

Figures

FIGURE 1. Crosniera wennerae sp. nov., female holotype, USNM 174403, TL 20 mm: A, lateral view of carapace; B, lateral view of abdomen showing segments 1 – 6; C, dorsal view of anterior carapace; D, antenna 1; E, major chela (right); F, gastric mill; G, minor chela (left); H, pereopod 3 with enlargement of propodus tip.

FIGURE 2. Crosniera wennerae sp. nov., female holotype, USNM 174403, TL 20 mm: A, maxilla 1; B, maxilla 2; C, maxilliped 1; D, enlargement of endopod of maxilliped 3; E, maxilliped 3; F, maxilliped 2; G, sixth abdominal segment with telson and uropods with enlargement of setation of exopod; H, right mandible; I, left mandible (palp missing); J, pleopod 1; K, pleopod 5 (exopod missing).

FIGURE 3. Crosniera wennerae sp. nov., female holotype, USNM 174403, TL 20 mm: branchial structures. A, single arthrobranch (third thoracomere); B, reduced podobranch (sixth thoracomere); C, two arthrobranchs (seventh thoracomere); D, epipod with detail of hooked setae at tip (sixth thoracomere); E, reduced epipod (seventh thoracomere).