Astrodendrum galapagense A. H. Clark 1916
Creators: name: Okanishi, Masanori
name: Fujita, Toshihiko
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Ophiuroidea
Euryalida
Gorgonocephalidae
Astrodendrum
Astrodendrum galapagense

description: Astrodendrum galapagense A. H. Clark, 1916
(Figs 10, 11)
Astrodendrum galapagensis A. H. Clark, 1916. 117;—Döderlein, 1927. 93; Downey, 1969. 49.
Type material. USNM 38581, holotype, collected by R/ V Albatross, between Santa Cruz and San Cristobal Islands, Galapagos Islands, Pacific Ocean, 00˚29.00’S, 89˚54.30’W, 717 m deep, 15 April 1888 (Fig. 1).
Diagnosis. External ossicles on aboral disc plate-shaped on periphery and conical in center, slightly in contact or separated; external ossicles on oral disc granular, separated; external ossicles on interradial lateral disc plateshaped, slightly in contact; bulges of lateral edges of proximal portion of arms absent; 2 terminal projections on each arm spine in proximal portion of arm; single secondary tooth on each hook-shaped arm spine in distal portion of arm.
Description of holotype. Disc. Disc five-lobed with notched interradial edges, 7.4 mm in disc diameter (Fig. 10A). Radial shields tumid (Fig. 10A, C). Aboral disc covered by skin embedding plate-shaped and conical external ossicles, both slightly in contact or separated (Fig. 10A). Plate-shaped external ossicles, approximately 140–400 µm in length at periphery of disc (Fig. 10B, C). Conical external ossicles approximately 110–150 µm in length at center of disc (Fig. 10B, C). Radial shields bar-like, covered by skin and external ossicles, approximately 3.5 mm in length, width 0.8 mm distally gradually decreasing to 0.5 mm proximally, shields, almost reaching disc center (Fig. 10A, B). Oral surface of disc covered by skin and granular external ossicles, separated and scattered, approximately 70–100 um in length (Fig. 10D–F). Oral shields triangular, 0.5 mm in length and height, adoral shields also triangular, 1.5 mm in length and 0.7 mm in height, oral plates long, bar-like, approximately 0.5 mm in length at outer end and 0.2 mm at inner end, and 1 mm in height (Fig. 10D). Ventral arm plates completely concealed by thick skin and external ossicles (Fig. 10D). Uniformly acute and spiniform teeth on dental plates, approximately 0.2–0.5 mm in length and 4 to 5 in number (Fig. 10E). One or 2 conical teeth on edge of each oral plate, approximately 0.1–0.2 mm in length (Fig. 10E). Interradial surface of lateral disc covered by granular external ossicles, slightly in contact, 50–150 um in length (Fig. 11A). Two genital slits (1.5 mm long and 0.2 mm wide) in each interradius, carrying no spinule ossicles along genital slit (Fig. 11A). Madreporite completely covered by skin and external ossicles and invisible in external view (Fig. 10D).
Arms. Arms 5, branching at least 7 times, but further branches indeterminate because of entanglement of arms. The first branch occurs beyond disc (Fig. 10A). On proximal portion of arm, the width and height approximately equal, 1.2 mm, with a concaved aboral surface and flattened oral surface. Arms tapering gradually toward arm tip (Fig. 10B–D). Aboral and lateral surface covered by granular external ossicles, slightly in contact, approximately 160–400 um in length (Fig. 11B). On each arm segment, a row of hooklet-bearing plates, approximately 800 µm in length on aboral and lateral sides (Fig. 11B). On middle portion of arm and subsequent distal segments, hookletbearing plates fully in contact with each other (Fig. 10C, D). Hooklets have single secondary tooth. Aboral and lateral surface devoid of external ossicles and covered only by skin (Fig. 10C, D). On proximal portion of arm, oral surface covered by granular external ossicles, separated and scattered, 30 µm in length (Fig. 11E). From middle to distal segments, the ossicles and only skin covering present. Throughout the arm, lateral arm plates and ventral arm plates completely concealed by skin and external ossicles (Fig. 11E). The first to third tentacle pores with no arm spine; fourth and subsequent pores have 2 (rarely 3) arm spines. In middle to distal portion of arm, the number of arm spines consistently 2. Those on proximal portion of arm ovoid, with up to 2 terminal projections (Fig. 11E). Inner arm spines, approximately half length of corresponding arm segment and outer spines approximately three quarters of inner spines in length (Fig. 11E). Those of middle portion of arm cylindrical, carrying 2 acute terminal projections, both inner and outer spines almost the same length as corresponding arm segment. Those of distal portion of arms transforming into hook, carrying single secondary tooth. Inner spines approximately half length of corresponding arm segment, and outer spines approximately half length of outer spines (Fig. 11D).
Color. Aboral surfaces uniformly brown, radial shields exceptionally white (Fig. 10A), oral surface uniformly white (Fig. 10D).
Distribution. REPUBLIC OF ECUADOR. Between Santa Cruz and San Cristobal Islands, Galapagos Islands, 717 m depth (Fig. 1) (Type locality, A. H. Clark, 1916).
Remarks. Astrodendrum galapagense can be distinguished from its congeners in having plate-shaped external ossicles, while the other five species lack plate-shaped ossicles on aboral surface of the disc. A. galapagense is unique in having a maximum of two terminal projections on the proximal portion of the arm; The number of projections is three in A. capense and A. elingamita, and 1 in A. sagaminum and A. spinulosum sp. nov. The maximum number of secondary teeth of hook-shaped external ossicles of distal portion of the arms of A. galapagense is one; A. capense and A. sagaminum have two, and A. elingamita and A. spinulosum have three (Table 1, see also remarks for A. spinulosum).
description: Published as part of Okanishi, Masanori & Fujita, Toshihiko, 2018, A taxonomic review of the genus Astrodendrum (Echinodermata, Ophiuroidea, Euryalida, Gorgonocephalidae) with description of a new species from Japan, pp. 289-310 in Zootaxa 4392 (2) on pages 304-307, DOI: 10.11646/zootaxa.4392.2.4, http://zenodo.org/record/1195409