WILLIAMS: NEW MARINE DECAPOD CRUSTACEANS 



dorsal ridge, stronger on right than on left; fin- 

 gers longer than palm, spooned at tips, prehensile 

 edges close fitting, entire, but small basal tooth of 

 fixed finger opposed by notch in prehensile edge 

 of dactyl. 



Walking legs rather long, first walking leg 

 (Fig. 8^) reaching almost to tip of chela, second 

 and third reaching about to base of dactyl on pre- 

 ceding leg; corresponding articles of respective 

 legs approximately equal in length except for 

 meri which decrease posteriorly; each merus with 

 rounded, rugose dorsal crest ending in distal 

 spine; each carpus with longitudinal dorsal and 

 dorsolateral rib ending in more or less well- 

 developed spine, and often with secondary 

 spine(s) on distal margin between them; each 

 propodus slender, bearing small movable spine 

 distolaterally at base of dactyl; each dactyl slen- 

 der, acute corneous tip preceded by row of 12 or 

 more movable spines on prehensile edge. Slender 

 fifth leg with well-developed cleaning brush on 

 more or less flattened dactyl opposed by similar 

 setae on distal end of propodus. 



Variation . — There is minor variation in orna- 

 mentation of the specimens available for study, 

 but none of it is associated with the disjunct dis- 

 tribution in the Golfo de California and the north- 

 eastern Pacific. 



Remarks. — The specimens reported here were 

 taken around hydrothermal vent sites discussed 

 by Canadian American Seamount Expedition 

 (1985), ASHES Expedition (1986), and Tunni- 

 cliffe et al. (1985, 1986). Munidopsis has been 

 sighted at three other sites along Juan de Fuca 

 Ridge, but the only specimens collected are those 

 listed above (V. Tunnicliffe^). 



Comparisons of Munidopsis alvisca with previ- 

 ously described species of the genus are aided by 

 reference to A. Milne Edwards (1880), Milne Ed- 

 wards and Bouvier (1897), Chace (1942), Sivert- 

 sen and Holthuis (1956), and Ambler (1980). Lack 

 of epipods on the pereopods immediately sepa- 

 rates M. alvisca from species such as M. crassa 

 Smith, 1885 and M. subsquamosa Henderson, 

 1885 which it superficially resembles. Both of the 

 latter species have relatively prominent rugae 

 and spines on the cephalothorax and legs whereas 

 M. alvisca has fairly smooth ornamentation on 



2Verena Tunnicliffe, Department of Biology, University of 

 Victoria, P.O. Box 1700, Victor, B.C., Canada V8W 2R2, pers. 

 commun. 1987. 



these body parts, except for minor development of 

 spines on the lateral carapace margin anteriorly. 

 The rostrum of all of these species is narrowly 

 triangular, curves moderately upward to the tip 

 and bears a middorsal carina, but the carina in 

 M. alvisca bears almost imperceptible scalelike 

 rugae and diminishes to obsolescence on the gas- 

 tric region whereas in both M. crassa and M. sub- 

 squamosa the carina is varyingly rugose, rather 

 strongly so in the former, and maintains this or- 

 namentation onto the gastric region. Moreover, 

 M. crassa bears tiny irregular marginal spines on 

 the rostrum. 



Spination of the merus of the third maxilliped 

 is far weaker in M. alvisca than in the other two 

 species discussed, and both the anterolateral 

 spine of the ischium and the crenulate margin of 

 the crest on the ischium are less developed than 

 in them. On the other hand, M. alvisca possesses 

 both mesiodorsal and mesioventral eye spines 

 whereas M. subsquamosa and M. crassa lack the 

 mesioventral spine. 



More distant comparisons seem inappropriate 

 because of different body proportions and orna- 

 mentation, rostral width, length, elevation and 

 spination, and structure of the eye and third max- 

 illiped. The keys for identification by both Chace 

 (1942) and Pequegnat and Pequegnat (1970), for 

 example, though strictly applicable to species of 

 the Atlantic basin, would ally M. alvisca with 

 M. aries (A. Milne Edwards, 1880), a much larger 

 species with broader cephalothorax and rostrum, 

 eyes almost hidden from dorsal view, and with 

 less transverse ornamentation. The revised ver- 

 sion of this key by Pequegnat and Pequegnat 

 (1971) would place M. alvisca in the couplet space 

 occupied by M. sundi Sivertsen and Holthuis, 

 1956, a species with superficially similar shaped 

 cephalothorax, but densely clothed with short 

 setae. 



Etymology. — The name is an acronym taken 

 from names of the deep submersible vessels used 

 in collecting the species, Alvin and Pisces IV. 



BRACHYURA: BYTHOGRAEIDAE 



Bythograea tnesatlantica new 

 species 



Figures 9, 10 



Materia/.— USNM 234300, Holotype 9, Mid- 

 Atlantic Rift Valley about 70 km south of Kane 



281 



