Alijinocaris dissimilis, Komai & Segonzac, 2005

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 : 1158-1163

AlIJinocaris dissimilis sp. nov.

( Figures 25 , 26 , 29 ) Alυinocaris breυitelsonis Kikuchi and Hashimoto 2000, p 136 (part), Figure 3 a–g. See ‘‘Remarks’’.

Material examined

Okinawa Trough. DS Shinkai 2000 : dive 547, Depression C, Minami Ensei Knoll, 28 ° 23.359N, 127 ° 38.389E, 705 m, 3 June 1991, suction sampler, coll. J. Hashimoto, one ovigerous female CL 9.7 mm (holotype; NSMT-Cr 15787) ; same data, one male 6.9 mm (paratype; NSMT-Cr 12456) ; same data, one ovigerous female CL 7.3 mm (paratype; NSMT-Cr 15788) ; same data, four males CL 5.1–8.4 mm (non-types; Dr T. Kikuchi’s collection) .

Description

Body moderately robust.

Rostrum ( Figure 25A, B ) directed forward, straight or very slightly curved dorsally, 0.53–0.61 of carapace length, usually reaching to second segment of antennular peduncle (rarely slightly overreaching distal margin of second segment); dorsal margin armed with 13–17 teeth, including 8–10 teeth on rostrum proper and five to eight relatively small teeth on carapace posterior to orbital margin, posteriormost tooth arising from 0.19–0.31 of carapace length; ventral margin armed with one or two small subdistal teeth. Carapace ( Figures 25A , 26A ) width 0.65–0.80 of length; postrostral median ridge moderately high, extending to 0.60–0.70 of carapace length, dorsal angle about 155 °; pterygostomian tooth weakly produced anteriorly, larger than antennal tooth, slightly exceeding antennal tooth; post-antennal groove shallow; branchial region not particularly inflated.

Third abdominal pleuron unarmed. Fourth abdominal pleuron ( Figure 25C ) with small posteroventral tooth and additional one or two teeth on posterior margin. Fifth abdominal somite similarly armed with strong posteroventral tooth and additional one to five tiny teeth on posterior margin or ventral margin. Sixth abdominal somite 1.30–1.40 times longer than height. Telson ( Figure 25D ) not reaching posterior margin of uropodal endopod, 2.70– 2.90 times as long as anterior width and 4.30–4.60 times as long as posterior width; armed with five to eight dorsolateral spines; posterior margin ( Figure 25E ) convex (rarely shallowly notched medially), armed with two pairs of spines at lateral corners and 12–14 plumose setae all longer than mesial pair of lateral spines.

Antennular peduncle ( Figure 25B ) stout, second segment 1.43–1.78 times longer than wide. Antennal scale ( Figure 26B ) 0.48–0.52 times as long as carapace, 1.90–2.16 times longer than wide; lateral margin straight, slightly converging against dorsal median ridge; distolateral tooth slender, directed forward, falling short of broadly rounded distal margin of blade.

First pereopod as illustrated ( Figure 26C ); greatest height of palm at most 0.40 times length of chela ( Figure 26D ); dactylus ( Figure 26D ) longer than palm. Third pereopod ( Figure 26E ) moderately slender; dactylus ( Figure 26F ) with accessory spinules notably increasing in size distally; carpus 0.60–0.65 times as long as propodus; merus about 6.4 times as long as greatest height.

Size

Largest male CL 8.4 mm; largest female CL 9.8 mm, ovigerous females CL 7.3–9.8 mm. Maximal TL ca 41 mm.

Variation

Variation in the rostral shape and dentition was illustrated by Kikuchi and Hashimoto (2000, Figure 3 a–g, as Alυinocaris breυitelsonis).

Distribution and habitat

Known only from Minami-Ensei Knoll, Mid-Okinawa Trough ( Figure 28 ), at a depth of 705 m. This new species occurs in a hydrothermally active area. Alυinocaris breυitelsonis and Shinkaicaris leurokolos comb. nov. occurred sympatrically with A. dissimilis (cf. Kikuchi and Hashimoto 2000).

Etymology

From the Latin dissimilis (different), indicating that this new species is quite different from A. breυitelsonis, with which the new species was confused in the original description.

Remarks

Re-examination of the type series of A. breυitelsonis disclosed that two species were confounded, one of which is described as new, A. dissimilis sp. nov. The true A. breυitelsonis is known only by the holotype. Furthermore, it has been found that non-type material referred to as A. breυitelsonis by Kikuchi and Hashimoto (2000) contains three species, A. dissimilis , Shinkaicaris leurokolos comb. nov. (cf. Kikuchi and Hashimoto 2000, Figure 3i ), and Opaepele sp. (cf. Kikuchi and Hashimoto 2000, Figure 3h ). Opaepele sp. is generally similar to Opaepele loihi Williams and Dobbs, 1995 , but more careful comparison is needed to determine the specific status.

Alυinocaris dissimilis sp. nov., A. markensis , A. muricola , and A. longirostris are morphologically very similar to one another. These four species share the rostrum reaching at least to the second segment of the antennular peduncle and armed usually with one or more ventral teeth, relatively high postrostral median ridge on the carapace, and the posterior margin of the telson with long plumose setae and two lateral pairs of spines. The differences among these four species are summarized in Table II. These characters should be used with caution, as most of them are useful only for adult specimens.

Although the proportional length and armature of the rostrum are highly variable in A. muricola (see Figures 8 , 10 , 11 ), the rostral characters are still useful for species discrimination. Female specimens of A. longirostris can be separated from females of A. muricola and both females and males of A. markensis by the proportionally longer rostrum (0.64–0.98 times as long as the carapace versus 0.30–0.70 times as long), which reaches or overreaches the anterior end of the antennular peduncle. The number of dorsal teeth on the rostrum (including those on the carapace) tends to be fewer in A. longirostris than in A. markensis and A. dissimilis (9–15 in the former versus 13–19 in the latter), although there is a partial overlap; the number greatly overlaps between A. longirostris and A. muricola . The ventral teeth of the rostrum are fewest in A. dissimilis sp. nov. among the four species compared (0–2 versus 4–13). However, the abnormality exhibited by A. muricola (the ventral margin of the rostrum is occasionally unarmed in large specimens with abnormally short rostra) diminishes the significance of this character.

The more posteriorly arising posteriormost dorsal tooth on the carapace is useful to distinguish A. longirostris from A. markensis and A. dissimilis sp. nov. In A. longirostris , the posteriormost tooth arises from 0.38–0.48 of the carapace length, while it is situated at 0.24–0.31 of the carapace length in A. markensis , 0.19–0.31 in A. dissimilis . The tooth tends to arise more posteriorly in A. muricola than in A. markensis and A. dissimilis (0.34–0.40 versus 0.19–0.31).

Adult specimens of A. muricola are characteristic in the somewhat inflated, notably convex branchial region of the carapace. Thus the ratio ‘‘carapace width/carapace length’’ is greater in A. muricola than in A. markensis and A. longirostris .

The post-antennal groove is more conspicuous in A. muricola than in the other three species.

The pterygostomian tooth of the carapace is less produced in A. dissimilis than in the other three species.

The second segment of the antennular peduncle is stouter in A. dissimilis sp. nov. and A. longirostris than in A. markensis and A. muricola (the ratios length/width are 1.43–1.78 in A. dissimilis sp. nov., 1.72–1.90 in A. longirostris , 1.79–2.05 in A. markensis and 1.90–2.10 in A. muricola ).

The antennal scale may be broader in A. longirostris than in the other three species (1.72– 1.90 times as long as wide versus 1.90–2.16 as long). Furthermore, the distolateral tooth of the antennal scale is somewhat directed anterolaterally in A. longirostris , rather than directed forward in the other three species.

Alυinocaris dissimilis sp. nov. also resembles Alυinocaris sp. 1, represented by the allotype of A. stactophila . In A. dissimilis sp. nov., the ventral margin of the rostrum is armed with one or two teeth or occasionally unarmed ( Kikuchi and Hashimoto 2000, as A. breυitelsonis). In Alυinocaris sp. 1, the ventral margin of the rostrum is unarmed. Alυinocaris dissimilis sp. nov. differs from Alυinocaris sp. 1 in the relatively long rostrum reaching the distal margin of the second segment of the antennular peduncle. Furthermore, the accessory spinules on the dactylus of the third pereopod are stouter in A. dissimilis sp. nov. than in Alυinocaris sp. 1 (cf. Figures 26F , 18E ). Examination of additional adult specimens will eventually reveal more differences between the two species.

Figures

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 8. Alυinocaris muricola Williams, 1988. (A) Carapace and cephalic appendages, lateral; (B) anterior part of carapace and cephalic appendages, dorsal; (C) second to sixth abdominal somites, lateral (setae omitted); (D) telson and left uropod, dorsal (marginal setae on uropod omitted); (E) posterior part of telson, dorsal; (F) left antennal scale, dorsal (marginal setae omitted). Female from West Florida Escarpment (CL 13.8 mm; Dr C. Van Dover’s collection).

Figure 10. Alυinocaris muricola 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 somites, lateral; (E) telson and right uropod, dorsal; (F) posterior part of telson, dorsal. Female from Régab site, west equatorial African margin (CL 16.8 mm; MNHN-Na 14277).

Figure 11. Alυinocaris muricola Williams, 1988. Variation in development and armature of rostrum. Specimens from Régab site, west equatorial African margin (Biozaïre 2). (A) Female, dive 146-09, slurp gun 3 (CL 11.0 mm; Ifremer); (B) female from same dive, slurp gun 2 (CL 21.0 mm; Ifremer); (C) female from same lot (CL 22.0 mm); (D) female from dive 147-10, slurp gun 1 (CL 21.6 mm; Ifremer); (E) male, dive 146, slurp gun 3 (CL 10.0 mm; Ifremer); (F) male (CL 16.2 mm; Ifremer); (G) male, dive 146, slurp gun 3 (CL 15.3 mm; Ifremer).

Figure 18. Alυinocaris sp. 1. (A) Right antennal scale, dorsal (marginal setae omitted); (B) right first pereopod, lateral; (C) chela of right first pereopod, outer; (D) right third pereopod, lateral; (E) dactylus and distal part of propodus of right third pereopod, lateral. Allotype female of Alυinocaris stactophila Williams, 1988 from Bush Hill hydrocarbon seep, Gulf of Mexico (CL 6.8 mm; USNM 234293).

Figure 25. Alυinocaris dissimilis sp. nov. (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 left uropod, dorsal (marginal setae on uropod omitted); (E) posterior margin of telson, dorsal. Holotype ovigerous female from Minami-Ensei Knoll, Mid-Okinawa Trough (CL 11.9 mm; NSMT-Cr 15787).

Figure 26. Alυinocaris dissimilis sp. nov. (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. Holotype ovigerous female from Minami- Ensei Knoll, Mid-Okinawa Trough (CL 11.9 mm; NSMT-Cr 15787).

Figure 28. Shinkaicaris leurokolos (Kikuchi and Hashimoto, 2000), comb. nov. (A) Left antennal scale, dorsal (marginal setae omitted); (B) left third maxilliped, lateral; (C) antepenultimate segment (merus–ischium–basis fused segment) of left third maxilliped, mesial; (D) coxa, epipod and basal part of antepenultimate segment of left third maxilliped, dorsal; (E) left first pereopod, lateral; (F) chela of left first pereopod, outer; (G) left third pereopod, lateral; (H) dactylus and distal part of propodus of left third pereopod, lateral; (I) same, ventral. Holotype female from Minami-Ensei Knoll, Mid-Okinawa Trough (CL 11.6 mm; NSMT-Cr 12457).

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