Radiella nidula sp. nov. Ekins, Erpenbeck & Hooper

Figures 1–3, Tables 1 & 3

Part Radiella irregularis Ridley & Dendy, 1886, sensu O’Hara et al. 2020: 4

? Radiella sarsii: sensu Burton 1959: 208.

Type material: Holotype QM G337524, off Byron Bay, New South Wales, Australia, -28.0544, 154.083 to -28.097, 154.081, 999–1013 m, Beam Trawl, Coll. Merrick Ekins on RV Investigator, Cruise IN2017_ V03, sample 100-114, 9/VI/2017.

Paratypes QM G337530, same collection data as QM G337524 sample 100-136; QM G337532, same collection data as QM G337524, sample 100-229; QM G339452, Coral Sea Commonwealth Marine Reserve, Queensland, Australia, -23.6312, 154.6597 to -23.659, 154.6438, 1770– 1761 m, Coll. Merrick Ekins on RV Investigator, Cruise IN2017_ V03, sample 128-117.2, 13/ VI /2017.

Other material: QM G337558, Coral Sea Commonwealth Marine Reserve, Queensland, Australia, -23.6312, 154.6597 to -23.659, 154.6438, 1770– 1761 m, Coll. Merrick Ekins on RV Investigator, Cruise IN2017_ V03, sample 128-117, 13/ VI /2017; QM G339453, same collection details as QM G337558, sample 128-117.3, 13/ VI /2017; QM G316421, Lord Howe Plateau, Pacific Ocean Seamounts, -32.445, 161.7825, 1130–1147 m, Beam Trawl, Coll. NORFANZ expedition on RV Tangaroa, TAN308/77-039, MF328, 25/ V /2003; QM G339455, same collection details as QM G316421, 14 specimens.

Etymology: named for its growth form, nidula L., small nest.

Diagnosis: A fringed multi-papillate dish shaped Radiella, with tracts of tylostyles from the choanosome diverging into bouquets supporting a top palisade layer of tylostyles, producing a two layered upper ectosome.

Morphology: The sponge is dish shaped varying from relatively flat to deeply conical, with a hispid concave upper surface, a convex smooth lower surface, and a marginal spicule fringe (Fig. 3 A–C). The holotype is 16.3 mm in width, including the 4.3 mm basal fringe, whilst the body height is 3.9 mm. The paratypes are identical in shape and similar in size i.e. 14–15.6 mm in width and 2.8–5.0 mm in height with the fringe of 3–4 mm. The holotype has three small papillae (1.4 mm in height), whilst 1–6 papillae could be discerned on the paratypes (Fig. 3 A). These may have been destroyed during collection as all of the specimens were covered by mud during the trawl collection. The sponge is white to cream in colour immediately after collection as well as in ethanol. The sponge is firm but flexible on the lower (basal) surface due to the later protective styles, but soft and compressible on the upper surface.

Skeleton: The choanosomal skeleton consists of randomly orientated disorganised smaller tylostyles, located between the tracts of principal styles (Fig. 3 C, D). The principal tylostyles originate in the lower ectosome, rise and form bouquets in the upper choanosome. The upper ectosome is formed by another layer of principal tylostyles forming a palisade (Fig. 3 D). Detritus including sand is caught in the spicules emerging through the palisade. The lower ectosomal skeleton also contains the long fringe tyles on the lower (basal) surface, which radiate from the centre of the lower surface forming the fringe (Fig. 3 C, D).

Spicules: The holotype has large, long, thin fringe styles 1990–4070 μm in length with slight central thickening and are 14.0–44.4 μm in width (Fig. 3 E–F). The principal tylostyles are much shorter, thicker, with a subtle tyle 779–1510 × 9.6–23.5 μm (Fig. 3 G–H). The smaller choanosomal tylostyles are thicker and have a more pronounced tyle and measure 220–658 μm in length and 4.8–19.4 μm in width (Fig. 3 I). The spicule measurements for the type material are tabulated in Table 1.

Distribution: Coral Sea and Tasman Sea seamounts, bathyal depth.

Ecology: Mud substrate

Molecular data: 28S-C region barcode of holotype QM G337524 (ENA Accession number OY741337), Paratypes QM G337530 (OY741338), QM G337532 (OY741339), forming a distinct and supported clade (Fig. 2).

Remarks: This new species superficially resembles Radiella straticulata (Wilson, 1925), however it differs markedly in the skeleton by lacking the three-layered stratification in both the upper and lower ectosome. It also differs by having a smaller fringe of only 3–4 mm compared to 6–9 mm, corresponding to the shorter fringe spicules of up to 4.3 mm in the new species and up to 10 mm in R. straticulata. This specimen was previously listed as Radiella irregularis in O’Hara et al. (2020).