Stegophiura ponderosa (Lyman, 1878)

Fig. 7A‒F

Ophioglypha ponderosa Lyman, 1878: 94‒94, pl. 2, figs. 52‒54.

Ophiura ponderosa. H.L. Clark 1911: 77‒79.

Amphiophiura ponderosa. Matsumoto 1917: 261.

Stegophiura ponderosa. Kyte 1987: 250‒252, fig. 1.

Material examined. Three individuals at three stations. TALUD III, Sta. 24, 1 ind. (ICML-EMU-9019); TALUD XII, Sta. 29, 1 ind. (ICML-EMU-11134-A); TALUD XIV, Sta. 7, 1 ind. (ICML-EMU-11694).

Comparative material. The type material was sought but not found in any collection (i.e., LACM, MCZ, NHMD, USNM; pers. comm. Tom Schiøtte & Penny Benson, 2016); it might be deposited in the British Natural History Museum (pers. comm. Sabine Stöhr & Timothy O’Hara, 2022), but we were unable to confirm this.

Description (ICML-EMU-11694). DD = 25.3 mm. Disc pentagonal, very swollen. Dorsal disc covered by irregular, very prominent, tuberculous, inflated right-angled plates. Primary plates not evident. RS longer than broad, triangular with right-angled edges, tuberculous, very swollen distally, with one lozenge-shaped elongated swollen plate inserted proximally (Fig. 7A). Ventral interradii covered by elongated, tuberculous plates. Genital slits with rectangular genital papillae (Fig. 7B), projecting dorsally and forming well-developed arm combs with quadrangular papillae. OSh longer than broad, constricted in the middle, rounded proximally and distally. Madreporite not evident. AdSh longer than broad, triangular, surrounding the OSh, meeting in front of OSh. Jaws bearing 5‒6 papillae at each side; BSc quadrangular; IPa quadrangular, slightly pointed; 2IPa 1‒2 quadrangular, slightly pointed; TPa two pointed, the apicalmost the largest. vT pointed, longer than oral papillae. Preceding ossicles slightly separated by a diastema; one rectangular and elongated AdShSp, three quadrangular 2AdShSp (Fig. 7C). Arms very swollen. DAP longer than broad, trapezoidal, with a prominent longitudinal keel, contiguous (Fig. 7D). VAP longer than broad, diamond shaped, contiguous. LAP with up to three ArSp, minute and similar size (approximately 1/5 LAP in length), blunt, several smaller accessory arm spines between them. First tentacle pore with 3‒4 rectangular TSc; subsequent tentacle pores with fewer TSc until reaching one distally (Fig. 7E). Color pattern white (ethanol preservation) (Fig. 7A‒F).

Habitat and distribution. Japan, Okhotsk Sea, Aleutians Islands, Alaska, California, USA, Mexico, and Chile; 73‒ 1,643 m depth, sandy, muddy bottoms, and gravel (H.L. Clark 1911; Kyte 1987; Maluf 1988; Lambert & Austin 2007; See Remarks). During the TALUD cruises collected in the Gulf of California and off Jalisco; 203‒ 1,643 m depth.

Remarks. Stegophiura ponderosa and A. superba can easily be confused due to their similar swollen appearance (Lambert & Austin 2007). However, they can be distinguished by: 1) longer radial shields in S. ponderosa (covering a little more than ½ a disc radius in S. ponderosa vs. covering almost ½ of the disc radius in A. superba), 2) lozenge-shaped, elongated swollen plate inserted proximally between the radial shields in S. ponderosa vs. diamond-shaped and flat plate in A. superba, 3) arm comb less conspicuous in S. ponderosa and with quadrangular papillae vs. more conspicuous and with pointed or quadrangular papillae in A. superba, 4) conspicuous longitudinal keel along the arms in S. ponderosa, 5) massive oral shields in A. superba, and 6) rectangular oral papillae in S. ponderosa vs. quadrangular and pointed in A. superba. Previously recorded in the Gulf of California and off Oaxaca (Granja-Fernández et al. 2015), it is now recorded off Jalisco and represents a new distribution record for this state. In addition, its depth distribution range is herein extended to 1,643 m.