Asbestopluma (Asbestopluma) desmophora Kelly & Vacelet, 2011

(Fig. 4, Tab. 2)

Material examined. NIWA 81376: Z15665, far eastern Solomon Islands, 12° S, 167° E, 1090 m, 10 Jan 2012, ROV (one large base plus several large branched pieces); NIWA 81377: Z15666, far eastern Solomon Islands, 12° S, 167° E, 1090 m, 9 Jan 2012, ROV (two bases and one broken branch).

Distribution. Macquarie Ridge (Australia EEZ, international waters); Chatham Rise, Hikurangi Plateau, Cavalli Seamount (New Zealand EEZ); Solomon Islands.

Diagnosis. Erect, arborescent sponge, about 100 mm high, branching dichotomously several times in a single plane, bearing numerous lateral filaments, sometimes with a brush or tassel-shaped end. Attachment base hard, devoid of filaments, densely packed and intermingled with desmas, and lined in places with a felt-work of microtylostrongyles. Megascleres desmas, and two size categories of mycalostyles, and small microtylostrongyles. Microscleres, two size categories of anisochelae, sigmas and sigmancistras (modified from Kelly & Vacelet 2011).

Description. Several specimens and fragments up to 110 mm high (Fig. 4 A, B). Attachment base slightly enlarged, preserved in three specimens only. Lower part of the axes 2.5 to 2.7 mm in diameter, devoid of filaments. Fine lateral filaments are well preserved and up to 4 mm long and 250 µm diameter at their base in NIWA 81377. Consistency of the lower stem and branches rigid, branches are fragile and easily broken. Color, white to cream. No aperture or aquiferous system visible.

Skeleton. Attachment base with densely packed and tightly intermingled desmas, fusiform styles and strongly curved substrongyles form a twisted axis in the basal part of the stem, which is lined with a felt-work of microtylostrongyles preserved in a few places. Lateral filaments have an axis of mycalostyles, and are frequently anchored through the main axis. Numerous large anisochelae line the main axis, whereas the small anisochelae and sigmancistras are numerous along the filaments.

Spicules. Megascleres (Fig. 4 C–D; Tab. 2), desmas (Fig. 4 E); 140–250 Μm. Mycalostyles I (Fig. 4 C left) from the main axis, sometimes substrongyles with a blunt point, fusiform; 875–1625 Μm. Mycalostyles II (Fig. 4 C right), of the filaments with a faintly marked head and an acerate, short point, straight, faintly fusiform, diameter often slightly irregular along the shaft; 410–755 x 8–15 µm. Acanthotylostrongyles (Fig. 4 D) from the basal part of the axis, irregularly curved, minutely spinose, with a round head and an abruptly blunt end; 45– 92 x 1–2 Μm.

Microscleres (Fig. 4 F–I; Tab. 2), anisochelae I (Fig. 4 F), palmate, head with the two alae entirely linked to the shaft, and a large, ovoid central tooth. Foot with two diverging, short conical teeth, with or without a short central tooth, giving a trilobate aspect; 38–52 Μm. Anisochelae II (Fig. 4 G), palmate, abundant, foot with a shaft bearing two round, poorly developed lateral alae, then strongly bent in a central tooth bearing two lateral expansions and ending in a small, conical tubercle; 9–12 Μm. Sigmancistras (Fig. 4 H) with two swellings along the shaft and a median depression; 17.5–25 Μm.

Substrate, depth range and ecology. Rocky substrate on hydrothermal vents at 1090 m, with a similar habitat to Abyssocladia lackwollii sp. nov. A few arborescent, dichotomously branching sponges, likely belonging to Asbestopluma (Asbestopluma) desmophora, have been observed on in situ photos from the ROV in the place of collection (Fig. 1 A, arrows). They appear to be less abundant than A. lakwollii sp. nov. in the collection area, and are found on horizontal, rather than vertical substrate.

Remarks. Asbestopluma (Asbestopluma) desmophora was first described from Seamount 9 Hjort, Macquarie Ridge (Australia EEZ) and to the north and south of the eastern New Zealand region (Chatham Rise, Hikurangi Plateau, and Cavalli Seamount) from 501 to 2675 m (Kelly & Vacelet 2011). Specimens from the far eastern Solomon Islands are remarkably similar in external form to their counterparts in the New Zealand region, and exhibit only minor variation in spicule complement. The mycalostyles I are here longer (875–1625 Μm) than in the type material (400–920 µm), in which they are usually shorter than 1000 µm (although one paratype has mycalostyles up to 1500 µm long), and the anisochelae I are also larger (38–52 µm versus 22–46 µm) and sometimes have a trilobate basal tooth instead of a bilobate one. The anisochelae II microscleres have a foot with a central tooth bearing a short tubercle rather than a point as in the more southern specimens (see Fig. 4 G & I), and no true sigmas were observed; however, these were rare or absent in most specimens of the type material. It is our opinion that these minor variations do not justify distinction of the Solomon Islands specimens at the species level, even though the result is a rather disjunct distribution for the species.

The Solomon Islands specimens also possess desmas in the attachment base, a character known only in two other species of Asbestopluma, A. (A.) inexpectata Lopes & Hajdu, 2014, from the southwest Atlantic; and A. (A.) bitrichela Lopes, Bravo & Hajdu, 2011, from Chile. Both species differ considerably from A. (A.) desmophora in the morphology and dimensions of all spicules, but particularly in the shape of the desmas and large anisochelae. Furthermore, A. (A.) inexpectata has an unusual mixture of anisochelae and isochelae.