Astrodendrum galapagense A. H. Clark, 1916

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 : 304-307

publication ID	https://doi.org/ 10.11646/zootaxa.4392.2.4
publication LSID	lsid:zoobank.org:pub:C1A8F758-D41A-404C-A5C4-6CBC476EA324
DOI	https://doi.org/10.5281/zenodo.5998503
persistent identifier	https://treatment.plazi.org/id/2526AA33-FF97-4165-D9C2-EB17FD7DD787
treatment provided by	Plazi
scientific name	Astrodendrum galapagense A. H. Clark, 1916
status

Treatment

Astrodendrum galapagense A. H. Clark, 1916 View in CoL

( Figs 10 View FIGURE 10 , 11 View FIGURE 11 )

Astrodendrum galapagensis A. H. Clark, 1916 View in CoL . 117;—Döderlein, 1927. 93; Downey, 1969. 49.

Type material. USNM 38581 View Materials , 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 View FIGURE 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 View FIGURE 10 ). Radial shields tumid ( Fig. 10A, C View FIGURE 10 ). Aboral disc covered by skin embedding plate-shaped and conical external ossicles, both slightly in contact or separated ( Fig. 10A View FIGURE 10 ). Plate-shaped external ossicles, approximately 140–400 µm in length at periphery of disc ( Fig. 10B, C View FIGURE 10 ). Conical external ossicles approximately 110–150 µm in length at center of disc ( Fig. 10B, C View FIGURE 10 ). 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 View FIGURE 10 ). Oral surface of disc covered by skin and granular external ossicles, separated and scattered, approximately 70–100 um in length ( Fig. 10D–F View FIGURE 10 ). 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 View FIGURE 10 ). Ventral arm plates completely concealed by thick skin and external ossicles ( Fig. 10D View FIGURE 10 ). Uniformly acute and spiniform teeth on dental plates, approximately 0.2–0.5 mm in length and 4 to 5 in number ( Fig. 10E View FIGURE 10 ). One or 2 conical teeth on edge of each oral plate, approximately 0.1–0.2 mm in length ( Fig. 10E View FIGURE 10 ). Interradial surface of lateral disc covered by granular external ossicles, slightly in contact, 50–150 um in length ( Fig. 11A View FIGURE 11 ). Two genital slits (1.5 mm long and 0.2 mm wide) in each interradius, carrying no spinule ossicles along genital slit ( Fig. 11A View FIGURE 11 ). Madreporite completely covered by skin and external ossicles and invisible in external view ( Fig. 10D View FIGURE 10 ).

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 View FIGURE 10 ). 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 View FIGURE 10 ). Aboral and lateral surface covered by granular external ossicles, slightly in contact, approximately 160–400 um in length ( Fig. 11B View FIGURE 11 ). On each arm segment, a row of hooklet-bearing plates, approximately 800 µm in length on aboral and lateral sides ( Fig. 11B View FIGURE 11 ). On middle portion of arm and subsequent distal segments, hookletbearing plates fully in contact with each other ( Fig. 10C, D View FIGURE 10 ). Hooklets have single secondary tooth. Aboral and lateral surface devoid of external ossicles and covered only by skin ( Fig. 10C, D View FIGURE 10 ). On proximal portion of arm, oral surface covered by granular external ossicles, separated and scattered, 30 µm in length ( Fig. 11E View FIGURE 11 ). 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 View FIGURE 11 ). 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 View FIGURE 11 ). Inner arm spines, approximately half length of corresponding arm segment and outer spines approximately three quarters of inner spines in length ( Fig. 11E View FIGURE 11 ). 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 View FIGURE 11 ).

Color. Aboral surfaces uniformly brown, radial shields exceptionally white ( Fig. 10A View FIGURE 10 ), oral surface uniformly white ( Fig. 10D View FIGURE 10 ).

Distribution. REPUBLIC OF ECUADOR. Between Santa Cruz and San Cristobal Islands, Galapagos Islands, 717 m depth ( Fig. 1 View FIGURE 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 ).