Benthesicymus, SPENCE BATE, 1881

BENTHESICYMUS SPENCE BATE, 1881 View in CoL

Emended diagnosis: Integument membraneous; rostrum overreaching distal corneal margin; carapace with developed branchiostegal spine set on anterior margin; pleon with fourth to sixth somitess dorsally carinate, fourth somite posteriorly crenate, sixth somite posterodorsally straight; telson with posterior, triangular end-piece between apical spines, with two to three pairs of moveable dorsolateral spines and a single pair of apical spines. First maxilliped with exopod distally abruptly narrowing to a segmented distal part; second maxilliped greatly expanded, less than three times as long as broad; third maxilliped with subtriangular dactylus bearing a single strong spine at tip. First pereopod with a distal tooth on basis and ischium; fourth and fifth pereopods with dactyl slender, entire. Thelycum with a strong sharp medial ventrally directed tooth on S6 or S8, S7 with a sharp protuberance projecting anteriorly far beyond this segment. Petasma with a fan-like serrate appendix on PI and PM greatly modified, PE not distally produced.

Species included: Benthesicymus crenatus Spence Bate, 1881 , Be. laciniatus Rathbun, 1906 .

Type species: Benthesicymus crenatus (subsequently designated by Spence Bate, 1888).

Remarks: Two species of this genus were described, but most of the distinguishing characters (see undated summary in: Yang & Chan, 2019) may be linked to observed specimens being of a different age. Indeed, individuals of Be. crenatus are generally larger, have the hepatic spine and more teeth on the rostrum and on the crenation of the fourth pleura. These characters included in the key below should, therefore, be considered cautiously. The only reliable character is the morphology of the thelycum in adults: the large tooth is present on S 6 in B. laciniatus or on S 8 in Be. crenatus . Regrettably, in most reports, the thelycum is not illustrated with necessary accuracy and in detail (e.g. Yang & Chan, 2019).

Geographical distribution: Central and North Pacific, North Atlantic, western Indian Ocean.