Ridleia echidna, Ekins & Erpenbeck & Wörheide & Hooper, 2023

Ekins, Merrick, Erpenbeck, Dirk, Wörheide, Gert & Hooper, John N. A., 2023, Deep Water Polymastiidae (Porifera, Polymastiida) from the South West Pacific, Zootaxa 5369 (1), pp. 57-88 : 74-76

Ridleia echidna sp. nov. Ekins, Erpenbeck & Hooper

urn:lsid:zoobank.org:act:A767CF2D-6D25-4945-B238-FE3BDD174D82

Figures 1 & 8

Part Radiella sp. QM 4942 sensu O’Hara et al. 2020: 4

Material examined: Holotype QM G337550 , Coral Sea Commonwealth Marine Reserve, Queensland, Australia, - 23.587, 154.194 to -23.617, 154.1947, 1013–1093 m, Beam Trawl, Coll. Merrick Ekins on RV Investigator, Cruise IN2017_ V03 , sample 121-149, 13/VI/2017.

Etymology: named for its spiky surface and its egg-like morphology reminiscent of the egg laying monotreme Echidna spp, L. ekinos, ‘sea urchin’.

Diagnosis: Egg shaped Ridleia with a dense palisade of very thin, long tylostyles making up more than 2/3 of the sponge thickness, embedded in the collagenous layer and a cavernous interior.

Morphology: Growth form of the single known specimen so far is flattened egg-shaped, 12 mm in length, 9 mm in width, and 5 mm in height ( Fig. 8 A ). Papillae were not found and presumably were lost during collection. The sponge is firm but compressible with a fine hispid layer.

Skeleton: This species is characterised by the massive palisade of large principal tylostyles almost 2 mm thick that makes up two thirds of the whole sponge body width ( Fig. 8 A–C ). These large ectosomal tylostyles are embedded in the collagenous layer. The small tylostyles also emerge from the collagenous layer and are orientated radially as the large tylostyles ( Fig. 8 C, D ). The lowest portion of the collagenous layer is characterised by the reduced and concentrated layer of tangential intermediate tylostyles. The inner choanosome has a cavernous interior with some residual tylostyle tracts ( Fig. 8 B, C ).

Spicules: The ectosome is composed mainly of the long thin tylostyles that characterise this new species (994– (1907)–3200 × 9.9–(15.6)–24.2 μm (n=54) ( Fig. 8 E,F ). The small tylostyles also make up the base of the ectosome (156–(296)–426 × 3.4–(7.5)–10.4 μm (n=36) ( Fig. 8 H ). The intermediate tylostyles make up the tangential outermost layer of the choanosome (448–(662)–1000 × 6.5–(10.5)–13.8 μm (n=22) ( Fig. 8 G ).

Distribution: Coral Sea, bathyal depths.

Ecology: Mud substrate.

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

Remarks: The holotype of Ridleia echidna sp. nov., QM G337550, is very different from the only two species remaining in this genus, i.e. R. oviformis Dendy, 1888 and R. dendyi de Laubenfels, 1934 . It differs from both other known species by its massive ectosomal palisade of tylostyles and the very reduced and concentrated layer of paratangential tylostyles. The choanosome has a cavernous interior with some residual tylostyle tracts. It is assigned to Polymastiidae based on the possession of several sizes of tylostyles, a distinct cortex, ectosome and internal spicule free choanosome. But it differs sensu stricto due to its primary styles being radial and the secondary styles are tangentially distributed. Ridleia is the closest genus we consider to allocate this new species, requiring confirmation based on molecular data from other species presently allocated to this genus.

Figures

FIGURE 1. Distribution of the specimens of species described herein as they were collected during the expeditions.

FIGURE 8. Ridleia echidna sp. nov. A. The upper surface of the holotype QM G337550 after fixation. B. Cross section through the holotype, showing the radial palisade of the long tylostyles and the collagenous base of the ectosome, as well as the cavernous choanosome. C. SEM of a cross section through the holotype, showing the radial palisade of the long tylostyles, the composition of the collagenous base and small tracts of tylostyles in the cavernous choanosome. D. SEM close-up of the long tylostyles forming the ectosomal palisade. E. The long ectosomal tylostyles. F. The magnified ends of the tylostyle in E. G. The intermediate tylostyles that form the tangential layer of the choanosome. H. The small tylostyles that radiate from the base of the ectosome.