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

AlIJinocaris longirostris Kikuchi and Ohta, 1995

( Figures 19 , 20 , 29 )

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

Alυinocaris longirostris Kikuchi and Ohta 1995, p 772 , Figures 1–7 [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 .

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) .

Description

Body relatively robust.

Rostrum ( Figure 19A, B ) 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 , 20A ) 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 ) 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 ) 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 ) 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 ) relatively stout, second segment 1.58–1.69 times longer than wide. Antennal scale ( Figure 20B ) 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 ) as illustrated; greatest height of palm about 0.40 times length of chela ( Figure 20D ); dactylus ( Figure 20D ) longer than palm. Third pereopod ( Figure 20E ) moderately slender; dactylus ( Figure 20F ) 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 ): 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.

Figures

Figure 1. Diagrammatic Alυinocaris, showing measurements used in text. (A) Carapace and rostrum, lateral; CL, carapace length; DA, dorsal angle; RL, rostral length. (B) Carapace, dorsal: CW, carapace width. (C) Anterior part of carapace and cephalic appendages, dorsal; L, length; W, width. (D) Sixth abdominal somite, lateral; L, length; H, height. (E) Telson, dorsal; AW, anterior width; L, length; PW, posterior width. (F) Antennal scale, dorsal; abbreviations as in (C). (G) Chela of first pereopod, lateral; PL, palm length; PH, palm height.

Figure 2. Alυinocaris muricola Williams, 1988. Left appendages. (A) Antennal scale, dorsal; (B) mandible, dorsal; (C) maxillule, ventral; (D) maxilla, ventral; (E) first maxilliped, ventral; (F) endopod of first maxilliped, dorsal; (G) second maxilliped, ventral; (H) first pleopod, ventrolateral; (I) endopod of first pleopod; (J) appendices interna and masculina of second pleopod, mesial. (A–H) Female from Régab site, west equatorial African margin (CL 16.8 mm; MNHN-Na 14277); (I, J) male from same locality (CL 15.4 mm; Ifremer).

Figure 3. Alυinocaris muricola Williams, 1988. Left thoracic appendages. (A) Third maxilliped, lateral; (B) coxa and antepenultimate segment of third maxilliped, dorsal; (C) first pereopod, lateral; (D) carpus of first pereopod, mesial; (E) second pereopod, lateral; (F) chela of second pereopod, dorsal; (G) third pereopod, lateral; (H) dactylus of third pereopod, lateral; (I) fourth pereopod, lateral; (J) fifth pereopod, lateral; (K) dactylus of fifth pereopod, lateral. Female from Régab site, west equatorial African margin (CL 16.8 mm; MNHN-Na 14277).

Figure 4. Alυinocaris lusca Williams and Chace, 1982. (A) Carapace and cephalic appendages, lateral (rostrum broken off); (B) anterior part of carapace and cephalic appendages, dorsal; (C) same, lateral; (D) carapace, dorsal (rostrum broken off); (E) third to sixth abdominal somites, lateral. (A, B, D, E) Paratype female from Rose Garden area, Galapagos Rift (CL 13.5 mm; USNM 184537); (C) paratype female (CL 8.6 mm; same lot).

Figure 5. Alυinocaris lusca Williams and Chace, 1982. (A) Telson and right uropod, dorsal; (B, C) posterior part of telson, dorsal; (D) right antennal scale, dorsal (marginal setae omitted); (E) first pereopod, lateral; (F) chela of first pereopod, outer; (G) left third pereopod, lateral; (H) dactylus and distal part of propodus of left third pereopod, lateral. (A, B, D–H) Paratype female from Rose Garden area, Galapagos Rift (CL 13.5 mm; USNM 184537); (C) paratype (CL 8.6 mm; same lot).

Figure 6. Alυinocaris markensis Williams, 1988. (A) Carapace and cephalic appendages, lateral; (B) anterior part of carapace and cephalic appendages, dorsal; (C) carapace, dorsal; (D) third to sixth abdominal somite, lateral; (E) telson and right uropod, dorsal; (F) posterior part of telson, dorsal. Female from site Les Ruches, Snake Pit, Mid-Atlantic Ridge (CL 16.7 mm; MNHN-Na 14282).

Figure 7. Alυinocaris markensis Williams, 1988. (A) Left antennal scale, dorsal; (B) left first pereopod, lateral; (C) chela of left first pereopod, outer; (D) left third pereopod, lateral; (E) dactylus and distal part of propodus of left third pereopod, lateral. Female from site Les Ruches, Snake Pit, Mid-Atlantic Ridge (CL 16.7 mm; MNHN- Na 14282).

Figure 9. Alυinocaris muricola Williams, 1988. (A) Carapace, dorsal; (B) left first pereopod, lateral; (C) chela of left first pereopod, inner; (D) left third pereopod, lateral; (E) dactylus and distal part of propodus of left third pereopod, lateral. Female from West Florida Escarpment (CL 13.8 mm; Dr C. Van Dover’s collection).

Figure 19. Alυinocaris longirostris Kikuchi and Ohta, 1995. (A) Carapace and cephalic appendages, lateral; (B) anterior part of carapace and cephalic appendages, dorsal; (C) third to sixth abdominal somites, lateral; (D) telson and right uropod, dorsal (marginal setae on uropod omitted); (E) posterior margin of telson, dorsal. Female from Iheya Ridge, Okinawa Trough (CL 17.9 mm; JAMSTEC).

Figure 20. Alυinocaris longirostris Kikuchi and Ohta, 1995 (A) Carapace, dorsal; (B) left antennal scale, dorsal (marginal setae omitted); (C) left first pereopod, lateral; (D) chela of left first pereopod, outer; (E) left third pereopod, lateral; (F) dactylus and distal part of propodus of left third pereopod, lateral. Female from Iheya Ridge, Okinawa Trough (CL 17.9 mm; JAMSTEC).

Figure 29. Distribution map of Alυinocaris species known at present.