Alvinocaris longirostris Kikuchi and Ohta, 1995

Li, Xinzheng, 2015, Report on two deep-water caridean shrimp species (Crustacea: Decapoda: Caridea: Alvinocarididae, Acanthephyridae) from the northeastern South China Sea, Zootaxa 3911 (1), pp. 130-138 : 132-135

Alvinocaris longirostris Kikuchi and Ohta, 1995

( Figs. 2–5 )

Alvinocaris longirostris Kikuchi and Ohta, 1995: 772 , figs. 1–7; Komai and Segonzac, 2005: 1148, figs. 19, 20, 29.

Material examined. 1 male (cl 12.35 mm), cold seep, Jiaolong Cold Seep I, ridge between continental shelf and slope, off Guangdong Province, China, southwest to Taiwan Island, northeastern South China Sea, 22°6.948’N, 119°17.116’E, 1138 m depth, collected with small net held by manipulator of “Jiaolong” submersible, collectors: Jian-wen Qiu and Xinzheng Li, 19 June 2013.

Description of specimen from the South China Sea. Large Alvinocaris shrimp.

Rostrum directed forward, very slightly curved dorsally, 0.50 of carapace length, distal part damaged, remaining part almost reaching to distal margin of second segment of antennular peduncle; dorsal margin armed with 11+ teeth, including 7+ teeth on rostrum proper and 4 relatively strong teeth on carapace posteriror to orbital margin, posteriormost tooth arising at anterior 0.39 of carapace length; ventral margin armed with 2+ small subdistal teeth. Carapace width 0.66 of length; postrostral median ridge moderately high, extending to 0.80 of carapace length, dorsal angle about 157°; pterygostomial tooth weakly produced anteriorly, shorter and more robust than antennal tooth, exceeding antennal tooth; post-antennal groove distinct; branchial region not particularly inflated.

Third abdominal pleuron unarmed. Fourth abdominal pleuron with small posteroventral tooth and 1 very small additional tooth on posterior margin and very 1 (right) or 2 (left) small additional teeth on ventral margin. Fifth abdominal pleuron armed with strong posteroventral tooth and 1 (left) or 3 (right) additional teeth on posterior margin. Sixth abdominal somite 0.43 times as long as carapace, 1.25 times longer than height, pleuron with strong posterolateral and posteroventral tooth. Telson 1.56 times as long as sixth abdominal somite, not reaching posterior margin of uropodal endopod, 2.33 times as long as anterior width and 4.30 times as long as posterior width; armed with 6 (right) or 8 (left) dorsolateral spines; posterior margin evenly slightly convex, armed with 1 (right) or 2 (left) spines similar to dorsolateral ones at lateral corners and 10 plumose setae all longer than mesial pair of lateral spines.

Eyes small, stalk short, cornea indistinct.

Antennular peduncle stout, stylocerite exceeding mid-length of second segment, distolateral tooth of first segment extending to proximal 0.40 of second segment; second segment 1.68 times longer than wide, distomesial tooth acute. Antennal scale 0.45 times as long as carapace, 1.82 times longer than wide; lateral margin straight, slightly converging against dorsal median ridge; distolateral tooth directed forward, falling short of broadly rounded distal margin of blade.

First and second pereopods symmetrical. First pereopod robust; greatest height of palm 1.18 times as long as length of palm; fingers strongly curved medially, dactylus 2.35 times as long as length of palm, carpus and merus unarmed. Second pereopod very slender, merus unarmed. Third pereopod moderately slender; dactylus 0.19 times as long as propodus, with accessory spinules notably increasing in size distally; carpus 0.72 times as long as propodus; merus 1.17 times as long as propodus, 5.92 times as long as greatest height, with a strong spine at middle ventral margin. Fourth and fifth pereopods similar to third, with merus unarmed.

Measurements. Carapace length= 12.35 mm; carapace width= 7.86 mm; rostrum length= 6.12 mm; telson length= 8.21 mm.

Colouration. Body entirely semi-transparent ivory-white, eyes white ( Figs. 2 , 3 ).

Remarks. The present male specimen agrees well with the original ( Kikuchi and Ohta, 1995) and Komai and Segonzac’s (2005) descriptions and illustrations. The similarities of nucleotide sequences of the genes 16S RNA and COI from the present specimen are more than 99% comparing with those provided by G. Tokuda, R. P. Kumara and H. Yamasaki [genbank number: AB821296.1 (mitochondrial DNA complete genome), fig. 4, COI, fig. 5, 16S RNA] and K. H. Chu and T.-Y. Chan [genbank number: GQ131897.1 (16S RNA)] from specimens from Okinawa Trough, Hatoma Knoll, the type locality.

Alvinocaris longirostris was not previously reported from the South China Sea. This record extends the distribution of the species much south into the South China Sea. As Komai and Segonzac (2005) pointed out, this species may be the only one in the family Alvinocarididae that occurs on both hot vents and cold seeps (see Teixeira et al. 2013). This record is the second record of the species from cold seep, after Fujikura et al. (1995) reported it from the Sagami Bay, at similar depth (1120–1220 m) as this record, although the species was first reported from hydrothermal vent.

Same as Alvinocaris longirostris Kikuchi and Ohta, 1995 , the two key species of the Bathymodiolus platifrons — Shinkaia crosnieri Community from the Jiaolong Cold Seep I, Bathymodiolus platifrons Hashimoto & Okutani, 1994 and Shinkaia crosnieri Baba & Williams, 1998 were also reported from Okinawa Trough in the habitat fluenced by hydrothermal vent. These three species are also the key species in the hydrothermal vent community.

Recently, the author visited the Jiaolong Cold Seep I again in April 2014 for field work with the scientific vessel “Kexue” using ROV “Faxian”, more specimens of Alvinocaris longirostris Kikuchi and Ohta , Bathymodiolus platifrons Hashimoto & Okutani, 1994 and Shinkaia crosnieri Baba & Williams, 1998 were collected.

The 14 known species of the genus Alvinocaris can be distinguished by the following key with caution as it is designed for identifying adult specimens. The key is modified after Komai & Segonzac’s (2005) key.

Figures

FIGURE 2. Habitat of the shrimp Alvinocaris longirostris Kikuchi and Ohta, 1995 in the Bathymodiolus platifrons -- Shinkaia crosnieri Community in the Jiaolong Cold Seep I, northeastern South China Sea. The shrimps were pointed by the arrows.

FIGURE 3. Alvinocaris longirostris Kikuchi and Ohta, 1995. Photo of the shrimp body.

FIGURE 4. COI gene sequences of Alvinocaris longirostris Kikuchi and Ohta, 1995. Up lines, based on material from Okinawa Trough, Hatoma Knoll, provided by G. Tokuda, R. P. Kumara and H. Yamasaki [genbank number: AB 821296.1]; low lines, present specimen.

FIGURE 5. 16 S RNA gene sequences of Alvinocaris longirostris Kikuchi and Ohta, 1995. Up line, based on material from Okinawa Trough, Hatoma Knoll, provided by G. Tokuda, R. P. Kumara and H. Yamasaki [genbank number: AB 821296.1]; low lines, present specimen.