Benthesicymus crenatus Bate, 1881

Yang, Chien-Hui & Chan, Tin-Yam, 2019, New records of Benthesicymus Bate, 1881 (Dendrobranchiata, Penaeoidea, Benthesicymidae) from the abyssal depths of Taiwan, ZooKeys 838, pp. 1-8 : 2-3

Benthesicymus crenatus Bate, 1881 Figs 1, 2

Benthesicymus crenatus Bate, 1881: 190 (type localities: central Pacific near Low Archipelago); Bate 1888: 329, pls. 54-55; Crosnier 1986: 851, figs. 6d-e, 7d-e, 8f-g; Kikuchi and Nemoto 1991: 67, figs. 2-3; Kim et al. 2000: 7, figs 2f, g, 8c.

Material examined.

"TAIWAN 2005", stn OCP296, 22°15.08'N, 121°55.09'E, 4430-4455 m, 10 Aug 2005, 2 females cl 29.2-37.3 mm (NTOU M02182). "TAIWAN 2008", stn CP413, 22°15.06'N, 121°54.98'E, 4412-4446 m, 12 Jun 2008, 2 males cl 34.2-53.7 mm (NTOU M02183); stn CP414, 22°37.91'N, 122°32.72'E, 5011-4990 m, 13 Jun 2008, 3 males cl 25.2-37.7 mm, 1 female cl 20.2 mm (NTOU M02184); stn CP415, 22°26.16'N, 122°21.10'E, 4813-4807 m, 14 Jun 2008, 3 males cl 25.8-48.6 mm (NTOU M02185); stn CP416, 22°26.44'N, 122°21.18'E, 4824-4807 m, 15 Jun 2008, 1 male cl 25.7 mm, 1 female cl 27.1 mm (NTOU M02186). "TAIWAN 2012", stn CP465, 22°37.56'N, 122°32.23'E, 5004-4996 m, 01 Jul 2012, 1 male cl 40.8 mm (NTOU M02187); stn CP466, 22°47.86'N, 122°29.72'E, 5226-5314 m, 02 Jun 2012, 2 males cl 28.1-33.3 mm, 3 females cl 20.1-37.3 mm (NTOU M02188); stn CP467, 22°48.01'N, 122°29.69'E, 5227-5154 m, 02 Jun 2012, 4 males cl 23.8-30.7 mm, 4 females cl 13.7-39.1 mm (NTOU M02189).

Description.

Integument membranous and soft. Rostrum dorsally compressed and slightly elevated into a low crest, dorsal margin with three or rarely four (only in one specimen of the present material) teeth, ventral margin without teeth. Antennal spine minute but distinct. Hepatic spine present with deep cervical groove behind it. Hepatic and branchiocardiac carinae elevated (Fig. 2A). Fourth to sixth abdominal somites with posteromedian spines. Posterior margin of fourth abdominal tergite distinctly crenate; with 19-33 (usually 23-28) teeth, medial teeth larger but obtuse (except for median tooth which is largest and acute) while lateral teeth sometimes sharper but smaller (Fig. 2B). Telson with three pairs of movable lateral spines and one pair of terminal spines, distal pair of lateral spine adjacent to terminal spine (Fig. 2C). Third maxilliped and first pereiopod both with merus and ischium bearing a sharp distomesial spine (Figs 2 D–E). Distal segment of third maxilliped with sharp spine at tip (Fig. 2F). Thelycum lacking seminal receptacles but bearing median longitudinal carinae on fifth and sixth thoracic sternites. Seventh and eight thoracic sternites with large tubercle and sharp median spine, respectively (Fig. 2G). Petasma with lateral lobe generally wide and flat, except for a long strong and narrow submarginal fold at ventrolateral lobule, another shorter subdistal fold also present on dorsolateral lobule; median lobe with distal margin minutely serrated (Fig. 2I), dorsomedian lobule strongly folded and densely covered with small hooked spines (Fig. 2H).

Coloration.

Body entirely reddish to orangish red (Fig. 1). Antennular and antennal flagella orange. Scaphocerite and bascerite pinkish white to pale white. Cornea white.

Distribution.

Northwest and Central Pacific, at depths of 3,530 to 6,350 m. There is one record of 0-5,700 m for this species ( Kikuchi and Nemoto 1991) but it is very likely that the material was collected from more than 3500 m deep.

Remarks.

The 27 specimens examined were collected from 4,412 to 5,134 m deep and most of them are damaged due to their fragile bodies even though their sizes are quite large. Nevertheless, they can be positively identified as B. crenatus by the characteristic comb-like crenation on the posterior margin of the fourth abdominal tergite. The Taiwanese material also generally fits well with previous descriptions of B. crenatus ( Bate 1881, 1888, Crosnier 1986, Kikuchi and Nemoto 1991, Kim et al. 2000). The present report of B. crenatus from 5,324 m represents the deepest marine animal recorded from Taiwan. The previous deepest records from Taiwanese waters were the squat lobsters ( Galatheidae Samouelle, 1819), Munidopsis profunda Baba, 2005 and M. taiwanica Osawa, Lin & Chan, 2008b from 5,011 m deep ( Osawa et al. 2008b, Baba et al. 2009).

The 15 species known in Benthesicymus ( De Grave and Fransen 2011) are often separated into two groups by the following characteristics: (1) branchiostegal spine not sharp and located at margin of carapace in group I vs. very sharp but situated behind the carapace margin in group II; (2) exopod of first maxilliped abruptly narrow to tip in group I vs. tapering to tip in group II; (3) merus of second maxilliped expanded in group I vs. unexpanded in group II; (4) dactylus of third maxilliped triangular with only one terminal spine in group I vs. subrectangular with more than one spine in group II; (5) exopods of all pereiopods small but visible in group I vs. very tiny in group II ( Burkenroad 1936, Kikuchi and Nemoto 1991). Groups I and II consist of ten and five species respectively, and B. crenatus belongs in group I.

The closest species to B. crenatus is B. laciniatus ( Crosnier 1986, Kikuchi and Nemoto 1991), which was also collected from Taiwan (see below). The two species can be readily separated by the following characters: (1) dorsal margin of rostrum armed with three or four teeth in B. crenatus (Fig. 2A) but with only two teeth in B. laciniatus (Fig. 3A); (2) hepatic spine present in B. crenatus (Fig. 2A) whereas absent in B. laciniatus (Fig. 3A); (3) cervical groove deep and with elevated branchiocardiac carina extending to posterior carapace in B. crenatus (Fig. 2A), carapace without deep groove nor distinct carina in B. laciniatus (Fig. 3A); (4) teeth on crenation of fourth abdominal pleuron more numerous (25-29 teeth) and rather blunt in B. crenatus (Fig. 2B), whereas fewer (13-19 teeth) and sharp in B. laciniatus (Fig. 3B); (6) posterior margin of fifth abdominal pleuron bearing distinct spine in B. laciniatus (Fig. 3B) whereas smooth in B. crenatus (Fig. 2B); (7) mesial margin of merus and ischium in third maxilliped and first pereiopod with a sharp spine in B. crenatus (Fig. 2 D–E), whereas without spine in B. laciniatus (Fig. 3D); (8) thelycum with strong median spine on eighth thoracic sternite in B. crenatus (Fig. 2G), whereas without spine in B. laciniatus ( Crosnier 1986: fig. 6c).