Dendrogaster jinshomaruae Saito & Wakabayashi, 2024

Saito, Nobuhiro, Moritaki, Takeya, Minakata, Keiji & Wakabayashi, Kaori, 2024, Three new species of sea star parasite Dendrogaster (Crustacea: Thecostraca) from Japan, Zootaxa 5405 (4), pp. 577-590 : 585-587

Dendrogaster jinshomaruae Saito & Wakabayashi sp. nov.

[New Japanese name: kanmuri-shidamushi]

( Figs. 1E , 4 , 5 )

Material examined. Holotype: ovigerous female (mantle size 18.8 mm), NSMT-Cr 31586 , removed from Coronaster volsellatus ( Sladen, 1889) (Echinodermata: Asteroidea: Forcipulatida : Asteriidae ) (unmeasured) (host specimen was not kept), off Kumano at either of two stations: St1 33°52’31.3 N 136°14’17.1 E, 210 m in depth; St2 33°54’54.5 N 136°15’26.5 E, 280 m in depth, Mie Prefecture , southeastern Kii Peninsula, Pacific coast of central Japan, coll. T. Moritaki on 24 March 2021.

Allotype: male (total length 6.17 mm), NSMT-Cr 31587, removed from the main branch of the paratype female, NSMT-Cr 31591.

Paratypes: one immature female (mantle size 9.6 mm), NSMT-Cr 31588, removed on 7 September 2020 from C. volsellatus (R 75 mm, r 15 mm), off Minami-ise (34°08’01.4”N, 136°30’14.8”E), Mie Prefecture , eastern Kii Peninsula , Pacific coast of central Japan, approximately 280 m in depth, coll. T. Moritaki, on 24 June 2018; 4 mature females (mantle size 14.2, 17.4, 30.8 mm, broken), NSMT-Cr 31589–31592 , removed on 24 March 2021 from unmeasured hosts, same collection information as the holotype. The host specimens were not kept .

Description of holotype female. Carapace (or mantle) markedly branched; surface smooth ( Fig. 4A, B ). Middle piece globular shaped. Pair of elongated stout main branches directed from base of middle piece, overall V-shaped; each main branch with 4 or 5 primary branches on each side arising oppositely with developed terminal protuberances.

Antennules 4-segmented and subchelate ( Fig. 4C ). First segment large, rectangular. Second segment triangular. Third segment rectangular, with fusion seam crossing proximal-dorsal angle and 2 spiniform setae at distal end of seam. Fourth segment rectangular, with movable terminal claw, large, cylindrical claw guard, and rudimentary proximal sensory process; bearing a pair of setae at dorsal and ventral base of terminal claw, 2 distal setae on claw guard, and 1 seta and 1 small aesthetasc on proximal sensory process.

Oral cone formed by labrum ensheathing maxillae. Maxillule and mandibles absent. Maxillae ( Fig. 4D ) harpoon-like, right and left maxillae fused medially for most of their length but separated distally, each with distal prongs and ventral hooks at apex. Distal prongs recurved laterally; ventral hooks reflected backwards.

Rudiments of thoracopods absent.

Eggs semi-oval, 0.52 mm (n=7).

Nauplius (outhonauplius) with bowl-shaped carapace, oval in dorsal view, 0.78× 0.48 mm; antennules, antennae, mandibles, labrum, and anal spine present; frontal filaments and medial knob, naupliar eye, maxillules, buds of thoracopods, caudal appendages, and abdominal spines absent. Antennules ( Fig. 4E ) uniramous with 4 indistinct segments, bearing 3 terminal setae. Antennae ( Fig. 4F ) biramous; exopod with 14 indistinct segments, bearing 2 terminal setae, and 1 long seta on each of distal 6 segments; endopod with 6 indistinct segments, bearing 3 terminal setae. Mandibles ( Fig. 4G ) biramous; exopod with 9 indistinct segments, bearing 2 terminal setae, and 1 long seta on each of 4 distal segments; endopod with 4 indistinct segments, 2 setae at distal end. Labrum pointed ventrally.

Description of allotype male. Carapace with pair of long, thick, more or less cylindrical posterior processes ( Fig. 5A ). Main body collapsed; anterior half comprised of antennules and an oral cone ( Fig. 5B ), posterior half missing.

Antennules similar to those of female ( Fig. 5B ): 2 long spiniform setae at distal end of seam on third segment; fourth segment with 2 setae, one at dorsal base of movable terminal claw and other 1 on lateral side of segment; 2 setae on cylindrical claw guard; and 1 small aesthetasc on proximal sensory process.

Ventral hooks tip of bifid maxillae reflected backwards ( Fig. 5B ).

Coloration. In living female specimen, mantle white-to-cream yellow ( Fig. 1E ).

Genetic information. K2P distances of the partial COI gene sequences determined from the holotype (NSMTCr 31586, GenBank No. PP118260) was 0.143 –0.382 from the other 7 species of Dendrogaster ( Table 1 ).

Ecological note. The host asteriid sea star, C. volsellatus ( Forcipulatida : Asteriidae ) is distributed in southern Japan, the East China Sea, and the southern Sea of Japan ( Imaoka et al. 1990), and is common in the bathyal zone of Kumano-nada ( Saba et al. 1982; T. Moritaki, personal communications). On 24 March 2021, 84 individuals of the sea star collected during “the survey of the Kumano-nada bathyal marine fauna” ( Moritaki 2020) were examined. Five of them were infected with Dendrogaster jinshomaruae sp. nov., thus, the prevalence was 6.0%. All female parasites infested the coelomic cavity of an arm of the host sea star. One male specimen was found from a paratype female. A few roe-like egg masses and a single nauplius were observed in the main branch of the holotype female, probably the eggs of this female were not fully developed. No ascothoracid larvae were found in any of the female parasites.

Interestingly, Asteriomyzostomum hercules Jimi, Moritaki & Kajihara, 2017 (Annelida: Myzostomida) is also known to parasitize in the cardiac stomach of C. volsellatus ( Jimi et al. 2017) . Simultaneous parasitism by Dendrogaster jinshomaruae sp. nov. and the endoparasitic annelid on a single host sea star was confirmed in this study: one case on the wild-caught sea star and another case on the sea star kept in a tank at Toba Aquarium (T. Moritaki, personal communications).

Etymology. The specific name is a Latin genitive noun honouring the fishing trawler Jinsho-maru, with a feminine ending appropriate for any ship.

Remarks. The whole V-shaped body of the female Dendrogaster jinshomaruae sp. nov. links to D. murmanensis Wagin, 1950 from Crossaster papposus ( Linnaeus, 1767) ( Solasteridae ) and Solaster endeca ( Linnaeus, 1771) ( Solasteridae ), and D. asterinae Achituv, 1971 from Asterina burtoni Gray, 1840 ( Asterinidae ) ( Wagin 1950; Achituv 1971). Dendrogaster jinshomaruae sp. nov. can be clearly distinguished from these congeners by 4 or 5 primary branches on each side of the main branches. The main branches do not arise on the anterior side of D. murmanensis , whereas D. asterinae arise more than 6 pair of primary branches on each side of the main branches.

Figures

FIGURE 1. The live state of one of the host sea stars and three new species of Dendrogaster found in this study. A, Neoferdina japonica (R 61.0 mm, r 14.2 mm), TAMBL-EC 35, infected with the holotype larvigerous female of Dendrogaster danni sp. nov. in the coelomic cavity. Photo by I. Dann; B, the holotype of Dendrogaster danni sp. nov. emerging from the coelomic cavity of the host sea star. Arrowhead indicates the middle piece. Photo by I. Dann; C, Dendrogaster danni sp. nov., holotype female (mantle size 66.4 mm), NSMT-Cr 31582; D, Dendrogaster tanabensis sp. nov., holotype female (mantle size 28.6 mm), NSMT-Cr 31584; E, Dendrogaster jinshomaruae sp. nov., holotype female (mantle size 18.8 mm), NSMT-Cr 31586.

FIGURE 4. Dendrogaster jinshomaruae sp. nov. A–D, holotype female, mantle size 18.8 mm, NSMT-Cr 31586, removed from coelomic cavity of Coronaster volsellatus (unmeasured), off Kumano, Mie Prefecture, southeastern Kii Peninsula, Pacific coast of central Japan, 210 to 280 m in depth. A, whole animal, dorsal view; B, dendrogram of holotype’s mantle branching pattern; C, left antennule, lateral view, segments numbered; D, fused maxillae. E–G, nauplius, body length 0.78 mm, NSMT-Cr 31593, removed from holotype female. E, antennule; F, antenna; G, mandible. Abbreviations: cg, claw guard; cl, terminal claw; fs, fusion seam; mb, main branches; mp, middle piece; sp, rudimentary proximal sensory process.

FIGURE 5. Dendrogaster jinshomaruae sp. nov., allotype male, total length 6.17 mm, NSMT-Cr 31587, removed from paratype female, NSMT-Cr 31591. A, whole animal; B, anterior part of main body, right lateral view, segments of antennule numbered. Abbreviations: at, antennule; cg, claw guard; cl, terminal claw; fs, fusion seam; mx, fused maxillae; sp, rudimentary proximal sensory process.