Chondrocladia (Chondrocladia) zygainadentonis Ekins, Erpenbeck & Hooper, 2020

Figures 2–3

Material examined: Holotype QM G337557, off Gladstone, Coral Sea, Queensland, Australia, Station 12, - 23.6311944 – -23.65900, 154.659694 – 154.643806, 1770– 1761 m, Beam Trawl, Coll. Merrick Ekins on RV Investigator, Cruise IN2017 _ V03, Sample 128-111, 13/vi/2017.

Other Material: QM G339304, Ribbon Reef 5, Canyon 8, Great Barrier Reef Queensland, Australia, - 15.36606511, 145.8662834, 1526.89 m, Site: S0378, Sample: 55, ROV SuBastian, Coll. Jeremy Horowitz on RV FALKOR, cruise FK200802, 14/8/2020

Distribution: This species is presently known only from the Coral Sea and Great Barrier Reef, off the Northeast coast of Queensland, bathyal depth.

Description:

Growth form: An erect delicate single-axis arborescent sponge resembling a tree consisting of a cylindrical stem with five columns of branches (Figs. 2 A, B). The sponge including the roots is 12 cm in height, the branches are up to 4 cm in length and the roots are also up to 4 cm in length. The stem base is short, only 12 mm in length and 2 mm in width. Each branch contains four alternate filaments (Fig. 2 C). The branches are between 0.5 and 1 mm in thickness. The filaments are up to 2.5 mm long and between 80 and 270 µm wide.

Colour: White in situ, on deck and preserved in ethanol.

Ectosomal skeleton: The ectosomal skeleton consists of a thin membrane containing chelae (Fig. 2 E).

Choanosomal skeleton: The choanosomal skeleton consists of bundles of mycalostyles longitudinally arranged in the axis of the stem. The stem also contains the subtylostyles and rare thin subtylostyles. The filaments consist of longitudinally arranged subtylostyles, with radial arrangement for support against the stem. The roots consist of the same combination of styles bundled together as in the stem, but also include a smaller blunt style (Fig. 2 F).

Megascleres: Larger mycalostyles with tapering ends and a blunt point (872-(1109)- 1280 x 14.9–(23.9)–36.0 µm, n=46) (Fig. 3 C, D). Subtylostyles with slightly swollen bases and tapering points (459–(558)–669 x 8.4– (12.2)–7.51 µm, n=34) (Figs. 3 E, F). Rare thin subtylostyles (479–(763)– 1060 x 3.0–(4.4)–6.3 µm, n=5) (Figs. 3 I, J). In the roots are blunt styles (149–(256)–371 x 1.0–(3.8)–7.1 µm, n=8) (Figs. 3 G, H).

Microscleres: Abundant small tridentate unguiferate isochelae with equal sized alae (25.5– (33.9)–42.9 x 2.1– (3.2)–4.5 µm, n=41) (Fig. 3 A). Uncommon large unguiferate isochelae, with variable dentation (often 3), 44.1– (53.9)–67.9 x 3.3–(5.7)–7.1 µm, n=16 (Fig. 3 B). Rare thin sigmas 23.1–(27.1)–31.1 x 0.9–(1.0)–1.2 µm, n=2 (Fig. 3 K). Rare sigmancistras 24.7–(26.5)–27.7 x 1.9–(2.5)–3.3 µm, n=4 (Fig. 3 L).

Remarks: Despite the appearance of the holotype resembling the gross morphology of Cladorhiza abyssicola Sars, 1872, C. (C.). zygainadentonis has isochelae, and it also lacks sigmas and sigmancistras. The presence of isochelae indicates it clearly belongs in Chondrocladia, as illustrated in the figures and the diagnosis of Hestetun et al. (2016a) and Ekins et al. (2020b). This species is Chondrocladia (Chondrocladia) zygainadentonis Ekins et al., 2020a, with the unique unguiferate anchorate isochelae. The only other Chondrocladia (Chondrocladia) with some sort of arborescent morphology is Chondrocladia (Chondrocladia) dichotoma Lévi, 1964; but that species has quadridentate unguiferate isochelae. The redescription of C. (C.). zygainadentonis includes the addition of the styles in the root like appendages.