Astrodendrum sagaminum ( Döderlein, 1902 )

Okanishi, Masanori & Fujita, Toshihiko, 2018, A taxonomic review of the genus Astrodendrum (Echinodermata, Ophiuroidea, Euryalida, Gorgonocephalidae) with description of a new species from Japan, Zootaxa 4392 (2), pp. 289-310 : 307-309

Astrodendrum sagaminum ( Döderlein, 1902)

( Figs 12 )

[Japanese Name: Tsuruboso-Tezurumozuru]

Gorgonocephalus sagaminus Döderlein, 1902 . 321–322;—H. L. Clark, 1911. 292–293; Jangoux et al., 1987. 308.

Astrodendrum sagaminum Döderlein, 1911 . 38–39, pl. 2 figs 3–5, pl. 7, fig. 8;—Döderlein, 1927. 32, 92; Bomford, 1913. 220; H. L. Clark, 1915. 185; Matsumoto, 1917. 73–74, fig. 21; Murakami, 1944. 247; Chang et al., 1962. 58–59, pl. 1, figs 3–4; Irimura, 1991. 120, 2 plates; Irimura & Kubodera, 1998. 138; Kroh, 2002. 148, 150–151, fig. 4–1.

Type material. ZSM 448 /1, one syntype, collected by Haberer, Sagami Bay , Japan, 1900 ( Fig. 1 ).

Diagnosis. Two sizes (larger and smaller) and scattered granular external ossicles on interradial aboral disc; uniform-size and fully in contact granular and conical external ossicles on radial shields; external ossicles conical, separated on interradial lateral disc; external ossicles plate-shaped and granular, both fully in contact on oral disc; bulges of lateral edges of proximal portion of arms absent; single terminal projection on each arm spine of proximal portion of arm; 2 secondary teeth on each hook-shaped arm spine of distal portion of arm.

Description of a syntype. Disc. Disc five-lobed with notched interradial edges, 20 mm disc diameter ( Fig. 12A ). Aborally, radial shields tumid ( Figs 12A ). On aboral disc, interradial spaces and spaces between each pair of radial shields entirely covered by different sizes (larger and smaller) of granular external ossicles, separated and scattered ( Fig. 12A ). Larger granular external ossicles approximately 150–200 µm in length, and smaller external ossicles approximately 50–100 µm in length ( Fig. 12A ). Radial shields covered by uniform-size external ossicles, fully in contact, approximately 100 µm in length ( Fig. 12A ), conical 100 µm high on distal edge of radial shields and granular in the other areas ( Fig. 12A ). Center of disc covered by larger granular external ossicles, approximately 250 µm and smaller granular external ossicles approximately 50–100 µm in length, both separated and scattered ( Fig. 12A ). Lateral edge of disc covered by uniform-size conical external ossicles, separated and scattered, approximately 100 µm in length and height ( Fig. 12A ). Radial shields completely concealed by external ossicles, bar-like, approximately 10 mm in length, 1.5 mm in width, and almost reaching disc center ( Fig. 12A ). Oral surface of disc covered by external ossicles, approximately 200–300 um in length ( Fig. 12B ), flat, polygonal and fully in contact on oral plate and slightly tumid, round and slightly in contact on adoral plates ( Fig. 12A ). Oral shields, adoral shields, oral plates and ventral arm plates completely concealed by external ossicles. Uniformly flat and spiniform teeth situated on the dental plates and edge of each oral plate, approximately 0.5–0.8 mm in length and approximately 20–25 in number on each jaw ( Fig. 12B ). Lateral surface of oral disc covered by conical external ossicles, separated and scattered, approximately 80–100 µm in length and height ( Fig. 12B, D ). Two genital slits (5 mm long and 1.5 mm wide) in each interradius ( Fig. 12D ). One elliptical madreporite situated on oral interradius, approximately 2.7 mm in length and 1.0 mm in height ( Fig. 12B ).

Arms. Arms 5, branching at least 8 times but number of branches indeterminate because of entanglement of arms ( Fig. 12C ). The first branch occurs beyond disc ( Fig. 12A, B ). On the proximal portion of the arm, width and height almost equal, 4.5 mm in width. Arms with a concave aboral surface and flattened oral surface. Arms tapering gradually toward arm tip ( Fig. 12C ).

On aboral and lateral surface of proximal portion of arm, each arm segment covered by granular external ossicles, fully in contact ( Fig. 12C ). On proximal portion of arms, granules 100–150 µm in length ( Fig. 12A ), gradually decreasing in size toward arm tip. Oral surface of proximal portion of arms covered by flat, polygonal plate-shaped external ossicles, similar to those on oral disc, approximately 200–300 µm in length ( Fig. 12C ). Before the first branches, the first to third tentacle pores with no arm spine; single arm spine at fourth pores ( Fig. 12B ), and subsequent pores with 2 or 3 arm spines ( Fig. 12B ).

Color. Uniformly creamy white ( Fig. 12 ).

Distribution. JAPAN. Sagami Bay (type locality, Döderlein, 1902; 1911; Matsumoto, 1917; Irimura, 1982, 1991; Jangoux et al., 1987), off eastern Japan (H. L. Clark, 1915); Suruga Bay (H. L. Clark, 1911; Döderlein, 1927; Kroh, 2002); Ogasawara or Yaeyama Islands ( Murakami, 1944: detailed locality is unknown). East China Sea ( Irimura & Kubodera, 1998). CHINA. East China Sea ( Chang et al., 1962). SRI LANKA. Southwest off Colombo ( Bomford, 1913). Depth ranges 90–1300 m ( Fig. 1 ).

Remarks. Astrodendrum sagaminum shares with A. spinulosum sp. nov. the presence of conical external ossicles, that are, separated and scattered on interradial lateral disc, while those of A. capense , A. elingamita and A. galapagense are plate-shaped and/or granular. A. laevigatum lacks external ossicles on the disc.

A. sagaminum and A. spinulosum sp. nov. can be distinguished by absence/presence of granular external ossicles on disc, absence/presence of bulges of lateral edges on the proximal portion of the arms, and the maximum number of secondary teeth on hook-shaped arm spines in distal portion of the arms (Table 1, see also remarks for A. spinulosum ).

Figures

FIGURE 1. Distribution of Astrodendrum spinulosum sp. nov., A. capense, A. elingamita, A. galapagense, A. laevigatum and A. sagaminum. Red symbols indicate type localities.

FIGURE 12. Astrodendrum sagaminum, one syntype (ZSM 448/1). A, aboral disc and proximal portion of the arms; B, oral disc and proximal portion of the arms; C, oral view of proximal portion of the arms; D, lateral view of the disc and proximal portion of the arms. Arrowheads indicate madreporite (B, D). Abbreviations: AS, arm spine; GS, genital slit.