Ptilocaulis ramosus Payne, Samaai & Gibbons 2025, sp. nov.

Ptilocaulis ramosus Payne, Samaai & Gibbons sp. nov. urn:lsid:zoobank.org:act: 083B370F-B75C-4244-9DAA-B6388C0DC22C Figure 7A–E, Table 5 Material examined. Holotype. SAMC-A096915 (cross-reference TS 2440 & WSL-INV74(6)): Walters Shoal Seamount, Grid WSL024, Station ALG10956, coll. RV Algoa, (33°08.8’ S; 43°49.1’ E) - (33°09.0’ S; 43°50.5’ E), 103–348 m depth, 29 May 2014. Paratypes. SAMC-A096919 (cross-reference TS 2448 & WSL-INV74(14)), SAMC-A097071 (cross-reference TS 2546 & WSL-INV74(28)), SAMC-A096928 (cross-reference TS 2570 & WSL-INV74(52)): Walters Shoal Seamount, Grid WSL024, Station ALG10956, coll. RV Algoa, (33°08.8’ S; 43°49.1’ E) - (33°09.0’ S; 43°50.5’ E), 103–348 m depth, 29 May 2014. SAMC-A096920 (cross-reference TS 2458 & WSL-INV114(1)): Walters Shoal Seamount, Grid WSL047, Station ALG10979, coll. RV Algoa, (33°09.7’ S; 43°58.4’ E) - (33°09.8’ S; 43°57.0’ E), 317–512 m depth, 03 June 2014. Type locality. Walters Shoal Seamount, south of Madagascar on the Madagascar Ridge, Western Indian Ocean (Fig. 1). Description (Fig. 7A). Erect, dichotomously branching form, with few scopiform flattened processes. Length 3.1 cm, width 3.2 cm and thickness 0.4 cm. Surface irregular and finely hispid (due to protruding spicules) with small circular oscules (<1 mm) scattered throughout. Spicules protruding <1 mm from the surface, thus fuzzy to the touch. Texture soft and spongy, compressible and easily torn. Colour in life yellow/ochre, white in preservative. Skeleton (Fig. 7B, C, D). Choanosomal skeleton consists of a dense interwoven mass of sinuous styles cored in fascicles. All axial spicules are disposed longitudinally in a plumose fashion. Spicule tracts are sometimes definable for only a very short distance before becoming obscured in the general mass. The peripheral region is short and not well formed. Peripheral spicules arranged individually, or multiple spicules branch tangentially to the axis in a plumoreticulated fashion and ascend to, and usually protrude through, the ectosome. Styles in the axial and peripheral skeleton do not appear to be differentiated, but are irregularly arranged. Specialized ectosomal skeleton absent. Spiculation (Table 5). Megascleres. Styles, smooth, bent to sinuous, variable and hastate to somewhat blunt distally, no easily discernible size classes: 796 (463–1385) × 19 (15–23) µm, n = 20 (Fig. 7E). Microscleres. Absent. Substratum, depth range and ecology. Five specimens found on rocky substrata in two sleds, predominantly composed of biogenic rubble, hydrozoans and non-living rhodoliths. Depth range: 103– 512 m. Etymology. Named for the branching form of the species: Latin ramosus (adj.A). Remarks. The present material conforms to Ptilocaulis Carter, 1883 as diagnosed by the presence of a vaguely reticulated axial skeleton and extra-axial skeleton formed by fibrofascicles cored with styles and ending in surface scopiform processes which are distinctive for this genus (Alvarez & Hooper 2002). There are nine currently accepted species of Ptilocaulis worldwide (de Voogd et al. 2024), of which only one, Ptilocaulis spiculifer (Lamarck, 1814), was also recorded from the WIO by Ridley (1884), Burton (1959), Pulitzer-Finali (1993) and the Red Sea by Lévi (1965). However, the type locality of P. spiculifer is King Island, Tasmania, Australia and the species has a much smaller spicule size range than that found for Ptilocaulis ramosus Payne, Samaai & Gibbons sp. nov.