Tentorium labium sp. nov. Ekins, Erpenbeck & Hooper

urn:lsid:zoobank.org:act: EFA69B47-C0D3-42AE-8821-40FEA45D7A72

Figures 1 & 7

? Tentorium semisuberites: Boury-Esnault & van Beveren 1982: 37–38, Pl. V (19), Figs. 8 F, G.

? Tentorium cf. semisuberites: Plotkin & Janussen 2008:119-122, Figs. 12, 13.

Material Examined: Holotype QM G337614, Central Eastern Commonwealth Marine Reserve, New South Wales, Australia, -30.0977, 153.8987 to -30.1193, 153.8745, 2429–2518 m, Beam Trawl, Coll. Merrick Ekins on RV Investigator, Cruise IN2017_ V03, 1 specimen, Sample 86-186, 5/VI/2017.

Etymology: named after the lip like appearance of the sponge L. labium, n. lip.

Diagnosis: Tentorium species, lacking the dense longitudinal sheath of tylostyles, with tracts of choanosomal principal styles not forming bouquets.

Morphology: The sponge is cylindrical in shape, with a domed upper surface (Fig. 7A–C). It is 10.6 mm in height and 30 mm in width. It is firmly attached to a piece of rock. It has three papillae located towards the apex of the smooth dome shaped upper surface (Fig. 7 A, B). Part of the ectosomal surface of the sponge was damaged, either during or before collection, so there may have been more papillae. The papilla is 4 mm in height and 1 mm in width. The sponge is cream in colour. The cortex is easily detachable and restricted to the upper surface, with the ectosomal skeleton composed of a palisade of tylostyles on the upper surface only (Fig. 7 A–D, I).

Skeleton: The choanosomal skeleton is composed of longitudinal tracts of approximately 20–400 μm in width, composed mainly of the large tylostyles (Fig. 7 D, I). These tracts travel to the surface and provide support within the papillae. The ectosomal cortex is composed entirely of the small sub/tylostyles forming a palisade that also covers the papillae (Fig. 7 D, I).

Spicules: The large principal styles that compose the longitudinal tracts in the choanosome are fusiform, with a subtle tylostyle head (Fig. 7 E–F). They are 743–(1227)–1931 × 13.9–(21.3)–32.1 μm (n=97).The ectosomal palisade forming tylostyles, are of a uniform thickness of style and are much smaller and thinner than the choanosomal tylostyles with a more obvious tylostyle head. Sometimes subtylote (Fig. 7 G–H). These tylostyles are 194–(237)– 303 × 2.9–(4.8)–6.4 μm (n=34).

Distribution: Continental slope of New South Wales, Australia, abyssal depth.

Ecology: Attached to rocks.

Molecular data: no unambiguous 28S-C region barcode could be generated from this species.

Remarks: The sponge lacks the basal fringe characteristic of Radiella species, but mentioned in some Tentorium descriptions (e.g. Boury-Esnault & van Beveren 1982). This species belongs to Tentorium, based on its columnar structure, with the longitudinally organised spicules and the palisade forming the upper ectosome. The genus is currently restricted to three species. Our specimen differs from T. papillatum (Kirkpatrick, 1908) (q.v. Plotkin & Janussen 2008), in lacking obvious papillae, but it bears a similarity to the latter species in that it lacks the dense cylindrical sheath of principal subtylostyles as in T. semisuberites (Schmidt, 1870) (q.v. Plotkin 2004) and T. levantinum Ilan, Gugel, Galil & Janussen, 2003, that was part of the original definition of Tentorium . Our specimen differs from the Arctic species Tentorium semisuberites (Schmidt, 1870) sensu stricto, in its gross morphology being an almost continuous dome structure, with an ectosome that can be easily detached. This individual specimen from the lower bathyal off the east coast of Australia, which has suffered some trauma to the superior surface, is closest to the as yet undescribed Tentorium cf. semisuberites sensu Plotkin & Janussen (2008), but differing from the latter in that the tracts in the choanosomal skeleton do not form obvious bouquets in the ectosomal skeleton – although this and the ectosomal sheath vary amongst specimens of Tentorium cf. semisuberites, as illustrated in Plotkin & Janussen (2008), suggesting there may be potentially several new species in this species complex. It is also almost three times larger at 30 mm in diameter, but of a similar height of 10.6 mm to Plotkin & Janussen’s (2008) material, and also differs in having three identical exhalant oscules and a cream colouration. Plotkin & Janussen (2008) also did not find differences in spicules between their specimens of T. semisuberites, collected from both hemispheres. However, due to the well-separated bipolar distribution of the Arctic and Antarctic faunas, it supports the possibility of being different species. Plotkin et al. (2016) showed that T. semisuberites is not a sister species to T. cf. semisuberites based on molecular data. Furthermore, Plotkin et al. (2018) showed that T. semisuberites is more closely related to Spinularia species than T. papillatum . Further molecular research may indicate sufficient differences for the erection of a separate genus and the placement of species within them. Tentorium semisuberites Boury-Esnault & van Beveren (1982) from the Kerguelen islands, has similar sized spicules, but differs by having fringing tylostyles at the base and only having a single papillae.