Hamacantha (Vomerula) melliflura, 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 : 388

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

Figs 1 , 4 , Table 2

urn:lsid:zoobank.org:act:70F21D5F-A08C-49D8-9F82-85751A920DCE

Material examined: Holotype: QM G316529 , Lord Howe Rise , New South Wales, Australia, -29.21783333, 159.0071667, 300 m, Trawl, Station 57, Reg 5, MF 253, Coll. Mathilde Richer de Forges on RV Tangaroa, NORFANZ expedition, 21/V/2003.

Etymology: mellifluous L. meaning “flowing with honey”, named for the flowing nature of the surface and the honeycombed texture of the sponge.

Description: The holotype is a fragile, lace-like, encrusting sponge, attached to a rock. It was originally 15 cm long, 6 cm wide and 3–4 mm in height. It has a very smooth surface, with five scattered oscules each approximately 3mm in diameter. The aquiferous channels radiating from the oscules are clearly visible through the transparent ectosome ( Fig. 4A ). The circular ostia are 0.3 mm in diameter and form rows/chains on the surface between the oscular-fed aquiferous channels ( Fig. 4B ). The external morphology resembles the common cloacal zooid formation on the ascidian Botrylloides . The sponge is white and translucent on deck and after preservation.

Skeleton: The ectosomal skeleton is composed of tangential styles, arranged in a multispicular reticulated pattern around the circular ostia. The small diancistras (II) and some of the large diancistras (I) occur on the underside of the ectosomal layer. The choanosomal skeleton consists of bundles of ascending styles supporting the ectosomal layer ( Fig. 4C ). The large diancistras form rosettes around the supporting bundles ( Fig. 4D ).

Spicules: The megascleres are styles, which are abundant, fusiform, straight, sharply pointed, and thickest in the centre. The blunt end is much narrower than the middle and has a rounded style end. They measure 301–(428)– 489 x 7.4–(12.2)–17.4 μm, n=30 ( Fig. 4 H, I ). The large diancistras (I) are common, with a subtle shaft twisted at the most 45 o, the thin sharp fimbriae running most of the length of the inner surface except for the middle quarter and around the notch ( Fig. 4E ). They measure 109–(127)–141 x 5.9–(8.2)–12.3 μm, n=39. The smaller thin diancistras (II) are less common, with the shaft twisted 90 o and bent in the centre ( Fig. 4F ). They have an almost incomplete ala, but with the fimbriae being extensive along the shaft. They measure 33.8–(46.2)–64.6 x 1.2–(2.1)–5.8 μm, n=35. The rare toxas are larger than the diancistras, and similar in length to the styles and measure 266–(298)–350 x 3.0–(4.5)–5.7 μm, n=5 ( Fig. 4G ).

Remarks: This new species is unique amongst the H. ( Vomerula ) species in having two sizes of diancistras along with the extra-large toxas, almost as long as the styles. The only other species in this subgenus with multiple diancistras and toxas are two species from the Atlantic, i.e. H. (V.) bowerbanki Lundbeck, 1902 and H. (V.) falcula ( Bowerbank, 1874) , both of which have three types of diancistras. Hamacantha (V.) tenda ( Schmidt, 1880) , from the Caribbean, has only a single class of diancistra and toxa. Hamacantha (V.) mellifura sp. nov. can be easily distinguished in the field by its distinctive external flowing appearance, and under the microscope by the rosette formation of the diancistras in the choanosomal skeleton.

Figures

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

FIGURE 4. Hamacantha (Vomerula) melliflura sp. nov. A. Holotype QM G316529 on deck. B. Ectosome, showing the ostia and the meandering solid tissue between the ostia, underneath which is the aquiferous channels. C. One of the aquiferous channels, formed by the arches of styles with rosettes of diancistras. D. Rosettes of diancistras around the bundles of styles. E. Large diancistras (I). F. Smaller diancistras (II). G. Toxa. H. Style. I. Magnified ends of the style as depicted in H.