Alvinocaris chelys, Komai, Tomoyuki & Chan, Tin-Yam, 2010

Komai, Tomoyuki & Chan, Tin-Yam, 2010, A new genus and two new species of alvinocaridid shrimps (Crustacea: Decapoda: Caridea) from a hydrothermal vent field off northeastern Taiwan *, Zootaxa 2372, pp. 15-32 : 16-24

publication ID	https://doi.org/ 10.5281/zenodo.275810
DOI	https://doi.org/10.5281/zenodo.6206517
persistent identifier	https://treatment.plazi.org/id/03E34C5D-FFDF-6712-FF23-760F3DE7F86F
treatment provided by	Plazi
scientific name	Alvinocaris chelys
status	sp. nov.

Treatment

Alvinocaris chelys View in CoL sp. nov.

( Figs. 1 View FIGURE 1 A–B, 2–6)

Material examined. Holotype: female (cl 9.6 mm), Gueishandao, Yilan County, Taiwan, stn KS 12, 24°49.682’N, 122°0.254’E, 300– 276 m, 4.IX.2008, 2.5 m beam trawl, NTOUM 0 0 782. Paratypes: same data as holotype, 2 females (cl 6.8– 8.5 mm), 1 ovigerous female (cl 9.3 mm), 4 males (cl 5.3–6.5 mm), NTOUM 0 0 783; same data, 1 female (cl 7.4 mm), 1 male (cl 8.5 mm), CBM-ZC 9572; stn KS 13, 24°51.231’N, 121°59.204’E, 252–275 m, 4.IX.2008, 2.5 m beam trawl, 1 male (cl 6.7 mm), NTOUM 0 0 784.

Description. Body ( Figs. 1 View FIGURE 1 A–B, 2) relatively robust; integument thin and soft, but not membranous; surface smooth.

Rostrum ( Figs. 3 View FIGURE 3 A–B, 6A–B) directed forward or slightly downward, straight, reaching distal margin of first segment of antennular peduncle to midlength of second segment (0.28–0.43 times as long as carapace in females, 0.39–0.45 times in males); dorsal margin sharply carinate, armed with 12–17 moderately small teeth, including 7–10 teeth on rostrum proper and 4–7 teeth on carapace posterior to level of orbital margin, posterior-most tooth arising at 0.19–0.24 of carapace length; ventral margin slightly convex to weakly carinate, unarmed or armed with 1 minute subterminal tooth; ventrolateral carina sharp, merging into orbital margin. Carapace ( Figs. 2 View FIGURE 2 , 3 View FIGURE 3 A–B, 6A–B) about 1.40 times longer than wide; postrostral median ridge moderately high to high (higher in females than in males), becoming blunt posterior to posteriormost tooth of dorsal rostral series, extending beyond midlength of carapace, sloping anteriorly to rostrum, dorsal angle up to 155°; antennal tooth moderately large; pterygostomial tooth strong, reaching well beyond antennal tooth; anterolateral margin between antennal and pterygostomial teeth concave; post-antennal groove shallow, diverging to horizontal plane of carapace; branchial region moderately convex.

Eighth thoracic sternite with long median spur directed anteroventrally.

Abdomen ( Fig. 2 View FIGURE 2 ) rounded dorsally; pleura of anterior three somites broadly rounded; fourth pleuron rounded posteroventrally or with subacute to blunt point; fifth pleuron with strong posteroventral tooth and with 1–3 additional denticles on posterolateral margin. Sixth abdominal somite 1.25–1.40 times longer than high. Telson ( Figs. 3 View FIGURE 3 C-D) not reaching posterior margin of uropodal endopod, length about 2.50 times anterior width and about 4.50 times posterior width; armed with 6–8 dorsolateral spines arranged in a slightly convex row on either side; posterior margin gently convex, armed with 2 pairs of spines at lateral angles (mesial spine about twice length of lateral spine) and 12–14 plumose setae all longer than mesial pair of lateral spines.

Eyes ( Figs. 3 View FIGURE 3 A–B) fused mesially, each with small tubercle on anterodorsal surface; corneal part imperfectly developed, ovate in outline, unfaceted though diffusely pigmented.

Antennular peduncle ( Figs. 3 View FIGURE 3 A–B, 6A) reaching or slightly overreaching distal margin of antennal scale. First segment with conspicuous proximal tubercle on dorsal surface laterally and strong distolateral tooth; dorsal surface with distinct obliquely longitudinal groove; stylocerite sharp, reaching to mid-length of second segment; distomesial margin with minute, but sharp tooth. Second segment stout, 1.30–1.40 times as long as wide, with small distomesial tooth. Lateral flagellum ( Fig. 2 View FIGURE 2 ) longer than carapace; mesial flagellum somewhat longer than lateral flagellum.

Antenna ( Figs. 3 View FIGURE 3 A–B, E) with stout basicerite bearing moderately strong ventrolateral and weak ventral teeth. Carpocerite stout, not reaching midlength of antennal scale. Antennal scale 0.38–0.42 times as long as carapace in females, 0.39–0.50 times in males, 1.75–1.80 times longer than wide; lateral margin nearly straight; middorsal ridge on dorsal surface slightly diverging against lateral margin; distolateral tooth moderately broad, falling short of broadly rounded distal margin of lamella.

Mouthparts typical of genus (cf. Komai & Segonzac 2005). Mandible ( Fig. 4 View FIGURE 4 A) with molar process terminating in blunt tip. Endopod of maxillule ( Fig. 4 View FIGURE 4 B) bearing long, setulose, apical setae on inner lobe. Maxilla ( Fig. 4 View FIGURE 4 C) with relatively broad scaphognathite. Exopod of first maxilliped ( Fig. 4 View FIGURE 4 D) broad, with weak mesial projection probably representing reduced flagellum. Second maxilliped ( Fig. 4 View FIGURE 4 E) relatively stout; epipod with bilobed podobranch. Third maxilliped ( Figs. 5 View FIGURE 5 A–C) overreaching antennal scale by about 0.50 length of ultimate segment; ultimate and penultimate segments combined arcuate; ultimate segment trigonal in cross section, subtruncate terminal margin with 2 or 3 spines; antepenultimate segment somewhat flattened dorsoventrally, sinuously curved in dorsal view, bearing 1 slender spine at ventrolateral distal angle; dorsal surface of antepenultimate segment with prominent tuft of short to long setae proximomesially, mesial surface with several vertical rows of short stiff setae distal to midlength; coxa stout, with small projection dorsal to base of epipod; epipod small, directed distolaterally, slightly bilobed.

First pereopod ( Figs. 5 View FIGURE 5 D–E, 6C–D) sexually dimorphic, larger in females than in males. Fingers curved downward and inward; outer surface of both fingers convex, inner surface concave, cutting edges uniformly offset, closing without gap, each armed with fine row of closely set teeth, tip of each finger slightly spooned; dactylus 1.4–1.7 times longer than palm in females, about 2.0 times in males, with submarginal row of short, curved setae on inner surface adjacent to cutting edge. Palm much shorter than fingers, with tuft of short setae at middle of ventral surface; short, distinct groove on ventral surface proximally. Carpus cupped distally to receive palm, with acute or subacute ventrodistal tooth; dorsodistal mesial margin rounded; ventromesial surface with patch of dense setae and 1 small spine just proximal to setal patch; mesial face shallowly depressed. Merus and ischium strongly obliquely articulated in lateral view; merus slightly inflated ventrally; ischium always unarmed.

Second pereopod ( Figs. 5 View FIGURE 5 F–G) shorter and more slender than first pereopod, not reaching distal margin of antennal scale. Fingers subequal to palm in length, each terminating in small corneous unguis crossing each other when closed, cutting edges without gap, each pectinated with single row of minute corneous teeth. Carpus slightly longer than chela. Merus and ischium obliquely articulated in lateral view. Ischium unarmed or armed with 1 spine ventrolaterally.

Third to fifth pereopods ( Figs. 5 View FIGURE 5 H, J–K) moderately slender, generally similar in structure and length although propodus becoming progressively longer, merus progressively shorter from third to fifth, third reaching beyond distal margin of antennal scale by 0.30–0.40 length of propodus. Dactyli ( Figs. 5 View FIGURE 5 I, L) small (0.15–0.18 of propodal length in third, 0.09–0.18 in fourth, 0.10–0.15 in fifth), 1.90–2.00 times longer than high, each armed with 3–6 accessory spinules arranged in single row on flexor margin. Propodi of third and fourth pereopods ( Fig. 5 View FIGURE 5 I) with slender spinules arranged in two rows on ventral surface; propodus of fifth pereopod ( Fig. 5 View FIGURE 5 L) with numerous spiniform setulose setae arranged in three or four rows on distal half of ventral surface. Carpi shorter than propodi. Meri armed usually with 1 spine ventrolaterally or rarely unarmed in third, armed with 1 spine or unarmed in fourth, always unarmed in fifth. Ischia always unarmed.

Male first pleopod ( Fig. 6 View FIGURE 6 E) with elongate distomesial lobe bearing 4 spiniform setae directed mesially or distomesially on mesial margin; lateral margin gently convex, with 6 spiniform setae in distal half and 5 or 6 setulose setae in proximal half; mesial margin faintly sinuous, with several setulose setae in proximal half. Appendix masculina ( Fig. 6 View FIGURE 6 F) moderately robust, almost as long as appendix interna, with about 5 spiniform setae terminally or subterminally. Appendices internae on second to fourth pleopods small, slender, tapering distally, without terminal cluster of cincinnuli, but that on fifth pleopod better developed than others, with terminal cluster of cincinnuli.

Protopod of uropod with acute posterolateral angle; endopod subequal in length to exopod; exopod with tiny posterolateral tooth and 1 movable spine just mesial to posterolateral tooth ( Fig. 3 View FIGURE 3 F).

Coloration. Body whitish translucent and patterned with numerous red dots except for flagella, third maxilliped, pereopods and pleopods ( Fig. 1 View FIGURE 1 A). Basal part of antennular flagella, third maxilliped and first pereopod with some red dots, while distal parts of antennular and antennal flagella, posterior pereopods and pleopods almost entirely lacking red dots. Red dots sometimes less numerous on rostrum, abdomen, antennular and antennal peduncles ( Fig. 1 View FIGURE 1 B). Eye light yellow with shiny reflection. Eggs reddish.

Variation. The postrostral ridge of the carapace is higher in spawning females than in non-spawning females and males. Rostral dentition is variable ( Table 1) as in other congeners. The posteroventral margin of the fourth abdominal pleuron varies from rounded to sharply pointed. The fifth abdominal pleuron is always armed with a strong posteroventral tooth and with one to four small additional teeth or denticles on the posterior margin. The antennal scale may be proportionally longer in males than in females. The stoutness of the cheliped of the first pereopod in alvinocaridids is known to vary allometrically but is usually not sexually dimorphic ( Komai & Segonzac 2005; but see Ahyong 2009). In the present new species, however, dimorphism appears sex related. All five females have stout chelae ( Figs. 5 View FIGURE 5 D–E, 6C), whereas the first chelae of all the five males are slender with elongate fingers (about twice length of the palm) ( Fig. 6 View FIGURE 6 D). Further specimens will be required to evaluate whether the dimorphism observed in the first pereopod is definitely sex related. Variation in the spination of the second to fourth pereopods is summarized in Table 1. It should be noted that the ischia of the third and fourth pereopods are always unarmed; the meri of the third and fourth pereopods bear at most one spine. The body color varies from red to white (COI sequence comparison between the two color forms, data not presented, shown no difference).

Station Sex type status cl (mm) rl/cl RTF P2 ischial spine P3 meral spines P3 ichial spine P4 meral spines P4 ischial spines left right left right left right left right left right

KS 12 female holotype 9.6 0.41 5+8/1 0 0 0 1 0 0 0 0 0 0 KS 12 female paratype 7.4 0.32 4+8/0 1 1 0 1 0 0 1 1 0 0 KS 12 female paratype 8.5 damaged 5+ 0 0 1 1 0 0 – – – – KS 12 female paratype 6.8 0.35 7+10/0 0 0 1 1 0 0 0 0 0 0 KS12 ovig paratype 9.3 0.28 7+7/1 1 1 1 1 0 0 0 0 0 0 KS 12 male paratype 8.5 0.39 7+10/0 1 1 1 – 0 0 1 – 0 – KS 12 male paratype 6.5 0.45 4+8/1 0 0 1 1 0 0 – 0 – 0 KS 12 male paratype 6.1 0.4 4+9/1 1 1 1 1 0 0 1 1 0 0 KS 12 male paratype 5.3 damaged 6+ 0 0 1 1 0 0 0 0 0 0 KS 13 male paratype 6.7 damaged – 0 0 0 0 0 0 0 0 0 0 Distribution. Known only from the type locality, Gueishandao, northeastern Taiwan, at depths of 252– 300 m.

Remarks. The present new species is very similar to Alvinocaris williamsi from the Mid-Atlantic Ridge. Shared characters include: the relatively robust body form; rostrum generally with one subterminal tooth or unarmed on the ventral margin; the possession of a row of plumose setae on the posterior margin of the telson; and a tendency for reduction of armature on the meri and ischia of the third to fifth pereopods. There are a few subtle morphological differences between the two species. The postrostral median ridge on the carapace extends beyond the midlength of the carapace in A. chelys , rather than not reaching or just reaching the midlength of the carapace in A. williamsi . The posteriormost tooth of the dorsal rostral series seems to arise more posteriorly in A. chelys than in A. williamsi (0.19–0.25 of the carapace length vs. 0.13–0.21). The telson is proportionally narrower in A. chelys than in A. williamsi (the length is more than 2.50 its width in A. chelys sp. n. vs. less than 2.50 in A. williamsi ). When large specimens (cl> 6.0 mm) are compared, the difference in the shape of telson is clear ( Fig. 3 View FIGURE 3 C vs. Komai & Segonzac 2005: Fig. 23D). The second segment of the antennular peduncle is proportionally more slender in the new species than in A. williamsi (1.30–1.40 times longer than wide versus 1.01–1.11 times).

This new species is also very similar to A. alexander from the Kermadec Ridge. Morphological differences between the two are also relatively minor. With regard to females, the postrostral median ridge of the carapace seems to be less strongly elevated in A. chelys than in A. alexander . This character, however, is expected to be variable ( Komai and Segonzac 2005), and should be used with caution, particularly in identifying young specimens. The armature on the ambulatory pereopods seems to be more reduced in the new species than in A. alexander . For example, in the new species, the ischia of the third pereopod are always unarmed, but are usually armed with 1 or 2 minute spines in A. alexander ; the merus of the same pereopod is unarmed or sometimes armed with 1 spine in A. chelys n. sp., rather than the usually bearing 2 spines in A. alexander . Among the present series of specimens of the new species, none has 2 spines on the merus of the third pereopods. The shape of the chela of the first pereopod is apparently sexually dimorphic in the two species, but the pattern is reversed between them. In A. chelys , females have stout chelae, but in A. alexander males have stout chelae ( Ahyong 2009).

Etymology. The name of the new species “ chelys ” (Greek, turtle), is after its type locality Gueishandao, which is the transliteration of “Turtle Mountain Island” in Chinese.