Dendrogaster komatsuae, Saito & Wakabayashi & Moritaki, 2020

Saito, Nobuhiro, Wakabayashi, Kaori & Moritaki, Takeya, 2020, Three New Species of Dendrogaster (Crustacea: Ascothoracida) Infecting Goniasterid Sea-Stars (Echinodermata: Asteroidea) from Japan, Species Diversity 25, pp. 75-87 : 77-78

Dendrogaster komatsuae sp. nov.

[New Japanese name: Yamatoishidatami-no-shidamushi]

( Figs 2 , 3 )

Material examined. Holotype: ovigerous female (mantle size 46.3 mm), NSMT-Cr 26858 , removed on 18 October 2015 from coelomic cavity of Lithosoma japonica Hayashi, 1952 (Echinodermata: Asteroidea: Valvatida : Goniasteridae ) (R 50.0 mm, r 25.3 mm), TAMBL-EC10 , off Owase, Kumano-nada Sea, Pacific coast of central Japan, about 300 m depth, by Kiei-maru on 13 January 2014.

Paratype: one ovigerous female (fragmented into main body and 3 pieces of mantle), NSMT-Cr 26859 , removed from coelomic cavity of the same host specimen as holotype.

No males were found from both the holotype and paratype.

Description of holotype female. Carapace (or mantle) markedly branched, surface smooth ( Fig. 2A, B ): mantle cavity filled with numerous eggs and nauplius larvae. Middle piece elliptical, 1.2 times as long as wide, subequal in length to each main branch. Pair of main branches directed laterally from base of middle piece, each 1.1 times as long as wide and dividing into 2 (anterior and posterior) primary branches. Primary branches quickly subdividing into cauliflower-like masses of short branches, with terminal branches blunt and rounded ( Fig. 2C ). Extra branch present opposite to middle piece, immediately dividing into pair of long posterior branches with distal parts subdivided in same manner as primary branches ( Fig. 2A, B ).

Antennules 4-segmented and subchelate ( Fig. 2D, E ). Second article trapezoidal. Third article elliptical, with fusion seam crossing proximal-dorsal angle and 2 short setae at distal end of seam (broken in left antennule). Fourth article rectangular, with movable terminal claw (missing in right antennule), large, cylindrical claw guard, and rudimentary posterior sensory process; bearing 3 short setae at dorsal, ventral and lateral bases of terminal claw (maybe broken in left antennule), 3 somewhat longer distal setae on cylindrical claw guard, and 2 setae (1 of it surely undeveloped aesthetascs) on posterior process.

Oral cone formed by labrum ensheathing second maxillae. First maxillae and mandibles absent. Second maxillae ( Fig. 2F ) harpoon-like, right and left members of pair fused medially for most of length but separate at distal end; terminal prong bifid with sharp tips.

Rudiments of thoracopods absent.

Eggs present in mantle cavity spherical, 0.52 mm in diameter (n=20).

Nauplius larvae from mantle cavity ( Fig. 3 ) with bowlshaped carapace, oval in dorsal view, 0.83× 0.66 mm (n=20); antennules, antennae, mandibles, labrum, and anal spine present; frontal filaments and medial knob, nauplius eye, maxillules, thoracic appendages, caudal appendages and rami, and abdominal spines absent. Antennules uniramous with 5 indistinct segments, bearing 3 terminal, 2 medial, and 1 lateral setae. Antennae biramous; exopod with 12 indistinct segments, each of distal 5 segments bearing 1 long seta; endopod with 5 indistinct segments, 4 setae at distal end. Mandibles biramous; exopod with 13 indistinct segments, distal 5 segments bearing 1 long seta; endopod with 5 indistinct segments, 4 setae at distal end. Labrum pointed posteriorly. No ascothoracid larvae were found.

Coloration. White to cream yellow (in ethanol-preserved specimens).

Infection parameters. The single damaged host specimen examined in the present study infected with 2 females.

Etymology. Named in honor of Emeritus Professor Miéko Komatsu, University of Toyama, Japan, for her significant contributions to the knowledge of echinoderm biology.

Diagnostic remarks. The presence of a bifid branch on the mature female opposite the middle piece links Dendrogaster komatsuae sp. nov. to three other congeneric species that also possess an ‘extra branch’ of some kind in this location: D. arbusculus ; D. dogieli Wagin, 1950 from Pteraster obscurus (Perrier, 1891) (Pterasteridae) ; D. otagoensis Palm- er, 1997 from Diplodontias miliaris (Gray, 1847) (Odontasteridae) ( Fisher 1911; Wagin 1950, 1976; Grygier 1982; Palmer 1997). Dendrogaster komatsuae sp. nov. can be separated from D. otagoensis by the immediate split of the extra branch into a pair of long posterior branches; D. otagoensis has just an unbranched rounded knob, mistakenly referred to as the ‘middle piece’ by Palmer (1997). Dendrogaster komatsuae can be separated from D. dogieli by the ramification pattern of the rest of the mantle, namely by the presence of anterior and posterior primary branches. In the main branches of D. dogieli are uniaxial with a bilateral series of distally smaller and simpler secondary branches. Dendrogaster komatsuae most closely resembles the Californian species D. arbusculus (see Fisher 1911; Grygier 1982) but is distinguished from it by the number of primary branches divided from main branch (two pairs in D. komatsuae sp. nov. vs. three pairs in D. arbusculus ), the length of the posterior branches on the extra branch (considerably longer in D. komatsuae ), and the condition of the terminal branches (blunt and rounded in D. komatsuae vs. conical and scattered in D. arbusculus ).

Figures

Fig. 2. Dendrogaster komatsuae sp. nov., holotype female, mantle size 46.3mm, NSMT-Cr 26858, removed from coelomic cavity of Lithosoma japonica (R 50.0mm, r 25.3mm), TAMBL-EC10, Kumano-nada Sea off Owase, Mie Prefecture, Pacific coast of central Japan, about 300m depth. A, whole animal, dorsal view; B, linear scheme to indicate a pattern of mantle branching; C, left anterior branches, unfurled; D, left antennule, medial view; E, third and fourth segments of right antennule (terminal claw missing), lateral view; F, second maxillae. Abbreviations: b1a, anterior primary branches; b2a, anterior secondary branches; bp, posterior branches; b1p, posterior primary branches; cg, claw guard; cl, terminal claw; eb, extra branch; fs, fusion seam; I–IV, segment numbers; mb, main branches; mp, middle piece; sp, rudimentary proximal sensory process; tb, terminal branch.

Fig. 3. Dendrogaster komatsuae sp. nov., nauplius, carapace length 0.87mm, from holotype female. A, whole animal, ventral view; B, left portion of body, ventral view.Abbreviations:a1, antennule; a2, antenna; md, mandible. Scale bar=0.3mm.