Alijinocaris longirostris, Kikuchi and Ohta, 1995

Komai, Tomoyuki & Segonzac, Michel, 2005, A revision of the genus AlIJinocaris Williams and Chace (Crustacea: Decapoda: Caridea: Alvinocarididae), with descriptions of a new genus and a new species of AlIJinocaris, Journal of Natural History 39 (15), pp. 1111-1175 : 1148-1151

publication ID	https://doi.org/ 10.1080/00222930400002499
persistent identifier	https://treatment.plazi.org/id/050D1914-FFEC-FF9A-FE9F-FCD9FECA4DBB
treatment provided by	Carolina
scientific name	Alijinocaris longirostris
status

Treatment

AlIJinocaris longirostris Kikuchi and Ohta, 1995

( Figures 19 View Figure 19 , 20 View Figure 20 , 29 View Figure 29 )

Alυinocaris sp.: Ohta 1990, Figure 6 View Figure 6 ; Kim and Ohta 1991, Figures 7 View Figure 7 , 9 View Figure 9 .

Alυinocaris longirostris Kikuchi and Ohta 1995, p 772 , Figures 1–7 View Figure 1 View Figure 2 View Figure 3 View Figure 4 View Figure 5 View Figure 6 View Figure 7 [type locality: Clam site on the Iheya Ridge, Okinawa Trough, 27 ° 32.709N, 126 ° 58.209E, 1360 m]; Fujikura et al. 1995, p 231 (Table 1), 232, 233 (Table 2), 234; Fujikura et al. 1996, p 136 (Table 1), 142; Hashimoto 1997, p 190; Watabe and Miyake 2000, p 32, Figure 4 View Figure 4 .

Material examined

Okinawa Trough. DS Shinkai 2000 : dive #1094, north-eastern slope of Iheya Ridge , 27 ° 47.1799N, 126 ° 54.0919E, 1053 m, 8 May 1999, coll. S. Tsuchida, seven females CL 8.1–16.9 mm (JAMSTEC 15968–15974) GoogleMaps .

Description

Body relatively robust.

Rostrum ( Figure 19A, B View Figure 19 ) directed forward or very slightly downward, nearly straight or slightly curved dorsally, 0.64–0.98 times carapace length, overreaching distal margin of second segment of antennular peduncle, sometimes overreaching distal margin of third segment; dorsal margin armed with 9–15 teeth, including 5–10 teeth on rostrum proper and four to seven relatively large teeth on carapace posterior to orbital margin, posteriormost tooth arising from 0.38–0.48 of carapace length; ventral margin armed with four to nine small teeth on anterior 0.30–0.40. Carapace ( Figures 19A View Figure 19 , 20A View Figure 20 ) 0.65–0.72 times as wide as long; postrostral median ridge high, extending to 0.75–0.80 of carapace length, dorsal angle about 150 °; pterygostomian tooth strongly produced anteriorly, far exceeding antennal tooth; post-antennal groove shallow; branchial region not particularly inflated.

Third abdominal pleuron smooth or with few minute denticles. Fourth abdominal pleuron ( Figure 19C View Figure 19 ) with one to four small teeth posterolaterally. Fifth abdominal somite similarly armed with one strong posteroventral tooth and additional two to five small teeth. Sixth abdominal somite 1.50–1.70 times longer than proximal height. Telson ( Figure 19D View Figure 19 ) falling slightly short of or reaching posterior margin of uropod, length about 2.53–2.80 times anterior width and 4.10–4.90 times posterior width; armed with five to seven dorsolateral spines on either side; posterior margin ( Figure 19E View Figure 19 ) always moderately convex, armed with two pairs of spines at lateral corner and 12–14 plumose setae all longer than mesial pair of lateral spines.

Antennular peduncle ( Figure 19B View Figure 19 ) relatively stout, second segment 1.58–1.69 times longer than wide. Antennal scale ( Figure 20B View Figure 20 ) about half length of carapace, 1.72–1.90 times longer than wide; lateral margin straight or slightly concave, somewhat diverging against dorsal median ridge; distolateral tooth directed rather laterally, falling short of broadly rounded distal margin of blade.

First pereopod ( Figure 20C View Figure 20 ) as illustrated; greatest height of palm about 0.40 times length of chela ( Figure 20D View Figure 20 ); dactylus ( Figure 20D View Figure 20 ) longer than palm. Third pereopod ( Figure 20E View Figure 20 ) moderately slender; dactylus ( Figure 20F View Figure 20 ) with accessory spinules increasing in size distally; carpus 0.60–0.65 times as long as propodus; merus 6.00–6.40 times as long as greatest height.

Size

Males were not available for study. Largest female CL 16.9 mm; TL ca 70 mm.

Variations

Variation in the armature of the pleuron of the third to fifth abdominal somites and the polymorphism of the first pereopod were described and figured by Kikuchi and Ohta (1995).

Distribution and habitat

Known from hydrothermally influenced areas in the Okinawa Trough ( Figure 29 View Figure 29 ): Iheya Ridge, at depths of 1053–1410 m; Hatoma Knoll, at depths of 1454–1627 m ( Kikuchi and Ohta 1995; Watabe and Miyake 2000; Ohta and Kim 2001). Also known from cold seeps at Off Hatsushima site, Sagami Bay, at depths of 1120–1220 m ( Fujikura et al. 1995). This is the sole representative of the Alvinocarididae that occurs both on hot vents and cold seeps.

Remarks

The type material was not re-examined, as the supplemental specimens from Iheya Ridge have been available for study. In the original description ( Kikuchi and Ohta 1995), Alυinocaris longirostris was characterized by the proportionally long rostrum which overreaches the distal end of the antennular peduncle, a relatively long stylocerite reaching to the midlength of the ultimate segment of the antennular peduncle, and the pattern of the armature of the second to fifth pereopods ( Kikuchi and Ohta 1995). Among these characters, only the rostrum is still useful in characterizing the species, although interspecific overlap is observed between A. longirostris , A. markensis , and A. muricola . The length of the stylocerite is not useful in characterizing A. longirostris because of intraspecific variation. As mentioned before, the armature of the second to fifth pereopods is not useful. Differences between A. longirostris and similar species are discussed under ‘‘Remarks’’ for A. dissimilis sp. nov.

Fujikura et al. (1995, 1996) reported the occurrence of A. longirostris at cold seeps in Sagami Bay, central Japan, Off Hatsushima site. The identification of the voucher specimens from Sagami Bay was made by Dr T. Kikuchi ( Fujikura et al. 1995, 1996), who described this species ( Kikuchi and Ohta 1995). It is remarkable that the site is a cold seep, although A. longirostris was originally described from hot vents. So far, there is no other alvinocaridid species that occurs on both hot vents and cold seeps. Nevertheless, Fujikura et al. (1996) recorded two further vent species known from Okinawa Trough, provannid gastropod Proυanna glabra Okutani, Tsuchida and Fujikura, 1992 and mytilid Bathymodiolus japonicus Hashimoto and Okutani, 1994 from Off Hatsushima site. They indicated the existence of high temperature anomalies at Off Hatsushima site. The authors also mentioned that no shrimp species was found at cold seeps on the Okinoyama Bank, about only 40 km east of Off Hatsushima site. Considering the rare occurrence of A. longirostris at Off Hatsushima site and the absence of the shrimp at the Okinoyama Bank, it is reasonable to consider that A. longirostris is primarily associated with vent environments.