Dendrogaster nagasakimaruae, 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 : 83-85

Dendrogaster nagasakimaruae sp. nov.

[New Japanese name: Otohimegokaku-no-shidamushi]

( Fig. 7 )

Material examined. Holotype: mature female (mantle size 22.0 mm), NSMT-Cr 26878 , removed from a coelomic cavity of Nymphaster euryplax Fisher, 1913 (Echinodermata: Asteroidea: Valvatida : Goniasteridae ) (R 60.0 mm, r 14.6 mm), East China Sea southeast of the Danjo Islands, Nagasaki Prefecture, Japan (31°51.73′N, 128°29.13′E), 247– 257 m depth, 6 March 2011, coll. K. Wakabayashi .

Allotype: male (total length 4.5 mm), NSMT-Cr 26879 , removed from main branch of holotype female.

Description of holotype female. Carapace (or mantle) markedly branched, surface smooth ( Fig. 7A, B ): mantle cavity filled with undeveloped eggs. Middle piece elliptical, 1.5 times as long as wide, 1.3 times as long as each main branch, and only 60% as wide basally as at point of greatest width. Pair of short, thick main branches directed laterally from base of middle piece, subequal in length to pair (anterior and posterior) of rather short, thick, widely outspread primary branches on each side. Each anterior primary branch giving rise to 2 (left) or 4 (right) secondary branches, arising alternately right sides and dichotomously on terminal of anterior primary branches. Short tertiary branches with lobe-like quaternary branches arising alternately on the second branches. Posterior primary branches extending laterally or posteriorly, 3 short secondary branches similar manner as anterior secondary branches arising alternately on each of the posterior primary branches. Ends of all branches bluntly rounded, without terminal protuberances.

Antennules 4-segmented, subchelate ( Fig. 7C ). Second article rectangular. Third article elliptical with curved ventral margin, fusion seam crossing proximal-dorsal angle, and 2 stout, spiniform setae at distal end of seam. Fourth article elliptical, with movable terminal claw, large, cylindrical claw guard, and rudimentary proximal sensory process; 1 seta at lateral to terminal claw, 3 distal setae on claw guard, and 2 setae (1 of it surely undeveloped aesthetascs) on rudimentary proximal process.

Oral cone formed by labrum ensheathing second maxillae. First maxillae and mandibles absent. Second maxillae harpoon-like ( Fig. 7D ), with right and left members of pair fused medially for most of length but separate distally, each with distal prong and ventral hook at apex. Distal prongs recurved laterally with medially bent tips, ventral hooks reflected backwards.

Rudimentary thoracopods absent.

Neither nauplius nor ascothoracid larvae found in mantle cavity.

Description of allotype male. Carapace ( Fig. 7E ) giving rise to pair of long, narrow posterior processes 6.2 times as long as wide, with lobes on basal part. Main body collapsed; abdomen and some thoracic limbs found, but antennules and oral cone missing.

Abdomen 5-segmented ( Fig. 7F ). Segments 1 and 2 rectangular, latter 1.5 times as long as former, penis invisible on first abdominal segment; segment 3 rectangular, subequal in length to segment 1; segment 4 short, one quarter as long as segment 3; segment 5 rectangular, 5 times as long as segment 4.

Furcal rami square and 4 longitudinal ridges on lateral surface, with 4 short distal setae on apex and 4 long medial setae.

Coloration. Female orange in life.

Infection parameters. One of 5 individuals of Nymphaster euryplax collected off southeast of Fukue-jima, the Goto Islands (a depth of 236–237 m) in October 2010 was infect- ed (the parasite lost). One specimen of N. euryplax collect- ed in 2011 was infected with the type series. Each of those hosts infected with single female.

Etymology. The specific name is a Latin genitive noun honoring the ship TR/V Nagasaki-maru, with the feminine ending appropriate for any ship.

Remarks. Dendrogaster nagasakimaruae sp. nov. can be clearly distinguished from the other species of this genus by the unique ramification pattern of the female mantle. This features 1) short and stout main branches, 2) thick roots of the two pairs of primary branches, and 3) alternate positioning of all secondary and tertiary branches. Furthermore, the proximal basal lobes on the posterior processes of male carapace are characteristic for this new species.

Figures

Fig. 7. Dendrogaster nagasakimaruae sp. nov., A–D, holotype female, mantle size 22.0mm, NSMT-Cr 26878, removed from coelomic cavity of Nymphaster euryplax (R 60.0mm, r 14.6mm), East China Sea southeast of Danjo Islands, Nagasaki Prefecture (31°51.73′N, 128°29.13′E), 247–257m depth. A, whole animal, dorsal view; B, linear scheme to indicate a pattern of mantle branching; C, left antennule, medial view; D, second maxillae, posterior view. E–F, allotype male, total length 4.5mm, NSMT-Cr 26879, removed from the main branch of holotype female. E, whole animal, right lateral view; F, abdomen. Abbreviations: b1a, anterior primary branches; b2a, anterior secondary branches; b3a, anterior tertiary branches; b1p, posterior primary branches; b2p, posterior secondary branches; bl, basal lobe; cg, claw guard; cl, terminal claw; fr, furcal rami; fs, fusion seam; I–IV, segment numbers; mb, main branches; mp, middle piece; pp, posterior processes; sp, rudimentary proximal sensory process.