Alvinocaridinides formosa, 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 : 26-31

publication ID	https://doi.org/ 10.5281/zenodo.275810
DOI	https://doi.org/10.5281/zenodo.6206523
persistent identifier	https://treatment.plazi.org/id/03E34C5D-FFD5-670B-FF23-72ED3EBEFA98
treatment provided by	Plazi
scientific name	Alvinocaridinides formosa
status	sp. nov.

Treatment

Alvinocaridinides formosa View in CoL sp. nov.

( Figs. 1 View FIGURE 1 C, 7–10)

Material examined. Holotype: Gueishandao, Yilan County, Taiwan, stn KS 13, 24°51.231’N, 121°59.204’E, 252–275 m, 4.IX.2008, 2.5 m beam trawl, female (cl 8.3 mm), NTOUM 0 0 785. Paratypes: same data as holotype, 1 female (carapace damaged, cl ca. 9.4 mm), NTOUM 0 0 786; same data, 1 female (cl 7.7 mm), CBM-ZC 9573.

Description. Females. Body ( Figs. 1 View FIGURE 1 B, 7) moderately robust; integument thin and soft, but not membranous; surface smooth.

Rostrum ( Figs. 8 View FIGURE 8 A–B, G–H) directed forward, reaching or slightly falling short of distal margin of first segment of antennular peduncle, somewhat depressed dorsoventrally, narrowly triangular in dorsal view; dorsal margin sloping down anteriorly, middorsal line elevated in blunt carina, armed with 6–8 tiny to small teeth, posteriormost tooth arising just above posterior margin of orbit; ventral surface nearly flat, unarmed; ventrolateral carina sharp, merging into orbital margin. Carapace ( Figs. 7 View FIGURE 7 , 8 View FIGURE 8 A–B, G) about 1.40 times longer than wide; postrostral median ridge absent; antennal tooth moderately large, buttressed with weak ridge; pterygostomial tooth slender, strongly produced, 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. 7 View FIGURE 7 ) rounded dorsally; pleura of anterior three somites rounded; fourth pleuron with small posteroventral tooth; fifth pleuron also with small posteroventral tooth and 1–4 additional denticles on posterolateral margin. Sixth somite about 1.20 times longer than height. Telson ( Figs. 8 View FIGURE 8 C–D) not reaching posterior margin of uropodal endopod, length about 2.40 times anterior width and about 3.3 times posterior width; armed with 7 or 8 dorsolateral spines arranged in sinuous row on either side; posterior margin convex, bearing 2 pairs of spines at lateral angles (mesial spine about twice length of lateral spine) and about 20 plumose setae all longer than mesial pair of lateral spines.

Eyes ( Figs. 8 View FIGURE 8 A–B) broadly fused mesially, each unarmed on anterodorsal surface; corneal part imperfectly developed, subovate in outline, unfaceted.

Antennular peduncle ( Figs. 8 View FIGURE 8 A–B, G) reaching or slightly overreaching distal margin of antennal scale. First segment with conspicuous proximal tubercle laterally on dorsal surface, strong distolateral tooth reaching nearly midlength of second segment, and small distomesial tooth; dorsal surface with distinct, obliquely longitudinal groove; stylocerite sharp, slender, reaching to mid-length of second segment. Second segment stout, about 1.40 times as long as wide, with small distomesial tooth. Flagella both longer than carapace.

Antenna ( Figs. 8 View FIGURE 8 A–B, G) with stout basicerite bearing moderately large ventrolateral and small ventral teeth. Carpocerite stout, reaching beyond midlength of antennal scale. Antennal scale ( Fig. 8 View FIGURE 8 E) 0.38–0.42 times as long as carapace, 1.80–1.90 times longer than wide; lateral margin nearly straight, noticeably diverging against middorsal ridge; middorsal ridge on dorsal surface conspicuous; distolateral tooth moderately broad; distal lamella produced, rounded, far overreaching distolateral tooth.

Mouthparts as illustrated. Mandible ( Fig. 9 View FIGURE 9 A) with molar process terminating in subacute tip. Maxillule ( Fig. 9 View FIGURE 9 B) with slightly bilobed endopod, inner lobe with 1 long setulose seta apically, outer lobe with 2 submarginal minute setae on outer surface. Maxilla ( Fig. 9 View FIGURE 9 C) with moderately broad scaphognathite. Exopod of first maxilliped ( Figs. 9 View FIGURE 9 D–E) broad, with small, distinct triangular lobe on mesial margin, representing reduced flagellum. Second maxilliped ( Fig. 9 View FIGURE 9 F) with stout endopod; epipod with stout podobranch abruptly tapering distally. Third maxilliped ( Figs. 10 View FIGURE 10 A–C) overreaching antennal scale by about 0.30 length of ultimate segment; ultimate and penultimate segment combined arcuate; ultimate segment distinctly longer than penultimate segment, trigonal in cross section, subtruncate terminal margin with 2 or 3 spines, lateral margin with longitudinal row of spiniform setae; 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 obliquely vertical tracts of short stiff setae distal to midlength; coxa stout, with small projection dorsal to base of epipod; epipod relatively large, directed distolaterally, subquadrate in dorsal view.

First pereopod ( Figs. 10 View FIGURE 10 D–F) reaching midlength of antennal scale, relatively slender. Chela small; fingers curved downward and inward, exceeding 4.0 times length of palm; outer surface of both fingers convex, inner concavity with opposed edges uniformly offset, closing without gap, each armed with fine row of closely set teeth, tip of each finger slightly spooned; palm without patch of setae on mesial surface. Carpus cupped distally to receive palm; dorsodistal mesial margin rounded; ventrolateral margin flared into ridge terminating in subacute tooth, ventromesial surface with grooming apparatus consisting of patch of dense setae and 1 small spine just proximal to setal patch; mesial face shallowly concave. Merus and ischium strongly obliquely articulated in lateral view.

Second pereopod ( Figs. 10 View FIGURE 10 G–H) slightly longer and more slender than first pereopod. Fingers slightly longer than palm, 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 longer than chela. Merus and ischium obliquely articulated in lateral view. Ischium unarmed.

Third to fifth pereopods ( Figs. 10 View FIGURE 10 I, L–M) moderately slender, generally similar in structure and length although propodus becoming progressively longer and merus progressively shorter from third to fifth, third extending beyond distal margin of antennal scale by 0.30–0.40 length of propodus. Dactyli ( Figs. 10 View FIGURE 10 J–K, N) small (0.20–0.22 of propodal length in third and fourth, 0.15–0.18 in fifth), 1.90–2.00 times longer than height, each armed with 10 or more corneous spines arranged in 2 or 3 rows on flexor surface. Propodi of third and fourth pereopods ( Figs. 10 View FIGURE 10 J–K) with slender spinules arranged in 2 rows on ventral surface; propodus of fifth pereopod ( Fig. 10 View FIGURE 10 N) with numerous spiniform setulose setae arranged in 3 or 4 rows on distal half of ventral surface. Carpi shorter than propodi. Meri and ischia always unarmed.

Appendices internae on second to fourth pleopods small, slender, those on second to fourth pleopods 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 slightly shorter than exopod; exopod with 2 movable spines at posterolateral angle ( Fig. 8 View FIGURE 8 F).

Coloration. Body whitish translucent. Antennules, antennal peduncles, carapace, abdominal somites and endopod of uropod slightly orangish-reddish. Eye light yellowish and with shiny reflection. Anterodorsal part of carapace behind orbit also with a large light yellowish shiny spot about two times larger than eye in size, visible through cuticle ( Fig. 1 View FIGURE 1 C).

Variation. Dentition of the fourth and fifth abdominal pleura is variable, as in other alvinocaridids. In the holotype, the left fourth pleuron bears a small but sharp posteroventral tooth, but the right is only minutely pointed at the posteroventral angle. In the smaller paratype (cl 7.7 mm, CBM-ZC 9573), each pleuron bears a small posteroventral tooth, but in the larger paratype (cl 9.4 mm, NTOUM), the left pleuron is rounded, while the right pleuron is angular at the posteroventral margin. The fifth pleuron is always armed with a posteroventral tooth, though the size of the tooth is rather variable; there are 1 to 3 additional small teeth or denticles on the posterior margin.

Distribution. Known only from the type locality: Gueishandao, northeastern Taiwan, 252– 275 m.

Remarks. This new species is very similar to Alvinocaris niwa from the Kermadec-Arc. In the description of the latter species, Webber (2004) highlighted the high degree of variability in taxonomic characters used in Alvinocaris , such as rostral length and spination, spination of the ischia and meri of the third and fourth pereopods, and the armature of the fourth and fifth abdominal pleura. However, Ahyong (2009) demonstrated that two species were present in the type series of A. niwa , describing the other as new A. alexander Ahyong, 2009 . Some of the conclusions of Webber (2004) regarding instability of taxonomic characters were probably derived from the composite type series of A. niwa . In spite of the close similarity, the present new species can be distinguished from A. niwa by completely lacking spines on the ischia of the second to fifth pereopods, and bearing 2 movable spines at the posterolateral angle of the uropodal exopod. In A. niwa, the ischium of the second pereopod is armed with 1 spine, and those of the third to fifth pereopods are generally armed with 1 or 2 spines; the uropodal exopod bears only 1 movable spine at the posterolateral angle ( Webber, 2004; personal observation). As mentioned in the Remarks of the genus, these characters, as exhibited by the new species, are possible synapomorphies uniting Alvinocaridinides with Shinkaicaris , Opaepele , Chorocaris and Rimicaris . Thus, A. niwa is excluded from this group. Furthermore, the posterior margin of the telson is evenly convex in the new species, instead of bilaterally convex with a shallow median notch or indentation in A. niwa, The second pereopod is more slender in the new species than in A. niwa ; the chela is shorter than the carpus in the new species vs. the opposite in A. niwa .