Hamacantha (Vomerula) ridleyi, Ekins & Baker & Hooper, 2023

Ekins, Merrick, Baker, Soraya & Hooper, John N. A., 2023, First records of Hamacantha species from seamounts off eastern Australia (Porifera, Demospongiae, Merliida), with description of four new species, Zootaxa 5318 (3), pp. 382-400 : 395

Hamacantha (Vomerula) ridleyi sp. nov. Ekins & Hooper

Figs 1 , 5 , Table 2

urn:lsid:zoobank.org:act:E525247D-8EA7-4EF5-9D81-4E288E2BFEE7

Material examined: Holotype: QM G327988 , Tasmanian Seamounts , off Huon Seamount, Tasmania, Australia, - 44.29226, 147.06693, 1100–1300 m, Sherman sled, on Solenosmilia variabilis habitat, SS0207-022-010, Z16, Coll. A. Williams and M. Schlacher on RV Southern Surveyor, SS 02/2007, 2/IV/2007.

Etymology: Named after Stuart Ridley, who described so many minute deep-water sponge species from the HMS Challenger and HMS Alert expeditions.

Description: Fragile, encrusting sponge growing on Solenosmilia variabilis approximately 30 mm x 10 mm x 2 mm in height ( Fig. 5 A, B ). The sponge had a smooth surface without any visible oscules. The sponge was white on deck and opaque white in ethanol preservative.

Skeleton: The ectosomal skeleton is a tangential array of styles ( Fig. 5C, D ). On the lower layer of the ectosomal skeleton are numerous diancistras of both sizes. The choanosomal skeleton consists of ascending bundles of styles that diverge to provide support to the ectosomal skeleton ( Fig. 5C ).

Spicules: The megascleres are styles, which are abundant, fusiform, straight, sharply pointed, and thickest in the centre ( Fig. 5H ). The blunt end is much narrower than the middle and has a rounded terminal tyle occasionally with a slight subtylostylote swelling. They measure 292–(385)–437 x 7.6–(9.9)–12.6 μm, n=35. The large diancistras (I) are common, with the shaft twisted at least 45 o, the thin sharp fimbriae run the entire length of the inner surface except around the notch ( Fig. 5E ). They measure 83–(96)–105 x 5.0–(8.8)–12.5 μm, n=42. The smaller diancistras (II) are also common, with the shaft twisted 90 o, have large, equal, almost touching curvaceous fimbriae ( Fig. 5G ). They measure 19–(24)–30 x 1.0–(1.1)–1.7 μm, n=29. Microscleres are small rare oxbow toxas that measure 48–(54)–65 x 2–(2)–2 μm, n=13 ( Fig. 5G ).

Remarks: The new species Hamacantha (V.) ridleyi sp. nov. is most similar to H. (V.) atoxa Lévi, 1993 ( Table 2 ), as they both have small diancistras but it differs from H. (V.) atoxa in having two sizes of diancistras rather than three diancistras in the latter species.The presence of toxas within Hamacatha species is limited to H. (V.) bowerbanki Lundbeck, 1902 , H. (V.) falcula ( Bowerbank, 1874) , H. (V.) melliflura sp. nov., H. (V.) papillata Vosmaer, 1885 and H. (V.) tenda ( Schmidt, 1880) . Of these species with toxas, the new species is closest to H. (V.) bowerbanki , but differs as H. (V.) bowerbanki has three categories of diancistras as well as the toxas.

Figures

FIGURE 1. Sampling sites of Hamacantha species described in this study.

FIGURE 5. Hamacantha (Vomerula) ridleyi sp. nov. A. Holotype QM G327988 on deck after collection. B. Holotype after fixation. C. Microscope section showing the bundles of styles in the choanosome supporting the tangential styles of the ectosome. D. Lower layer of the ectosome showing the tangential styles and the interspersed diancistras. E. Large diancistras (I). F. Small diancistras (II). G. Toxa. H. Style. I. Magnified ends of the style depicted in H.