Rhizaxinella cf. nuda Wilson, 1925

Plotkin, Alexander S. & Janussen, Dorte, 2008, Polymastiidae and Suberitidae (Porifera: Demospongiae: Hadromerida) of the deep Weddell Sea, Antarctic *, Zootaxa 1866, pp. 95-135 : 126-128

Rhizaxinella cf. nuda Wilson, 1925 ( Fig. 15 )

Synonymy

Rhizaxinella nuda— Wilson 1925: 352 –353, pl. 38 (fig. 5).

Description

External morphology. Small club­shaped sponges with rather damaged stalks (figs. 15A–E). Their height varies from 0.6 to 2.1 cm. The surface is velvety, greyish. Consistency is rather soft. A contracted osculum is located slightly eccentrically on the top of main body.

Skeleton. The choanosomal skeleton is constituted by the principal tylostyles arranged more or less radially and grouped in tracts or bundles (fig. 15F). The ectosomal skeleton is formed by the bouquets of small tylostyles, densely packed and intermingled. Skeleton of the stalk not observed because of considerable damage of the latter.

Spicules. Altogether 120 spicules from 2 specimens were measured. Two size categories are well distinguished. The number of measured spicules of each category is given below, separately for each specimen (n1, n2).

Both principal and ectosomal spicules possess well­developed spherical tyles. Principal tylostyles are slightly fusiform and straight (fig. 15G). Their dimensions are: length 1150­1759 ­2318 µm, tyle diameter 17­ 18.9­21 µm, diameter of the shaft underneath the tyle 13­14.3­15 µm, maximal diameter of the shaft 13­16.2­ 21 µm (n1=30, n2=30). Ectosomal tylostyles are isodiametric, straight or slightly curved (fig. 15H). They measure: length 450­551­690 µm, tyle diameter 9­13.7­18 µm, diameter of the shaft underneath the tyle 7­ 9.0­11 µm, maximal diameter of the shaft 8­10.1­13 µm (n1=30, n2=30). Spicules of the stalk were not observed.

Type locality: NW Pacific: Philippines: Mindanau Island: Iligan Bay, 814 m.

Distribution (other than type locality): NW Pacific: Philippines: E. Cebu, 710 m ( Lévi 1964).

Antarctic: Northern Weddell Sea, 2080–2620 m (present study).

Remarks

We allocated the specimens studied to R. nuda due to the similarities of main body shape and skeleton architecture. However, it was done with some doubt because our sponges have smaller ectosomal tylostyles and thinner principal tylostyles than those described by Wilson (1925) and also we did not observe the stalk skeleton. On the other hand, our specimens differ quite noticeably from the Southern Hemisphere species R. australiensis Hentschel, 1909 . The latter is characterized by the branching, anastomosing body and smaller sizes of both principal and ectosomal spicules than those of the specimens described herein.

Figures

FIGURE 15. Rhizaxinella cf. nuda. A – one specimen SMF 10597. B – the other specimen SMF 10597. C – specimen SMF 10588. D – specimen SMF 10581. E – specimen SMF 10580. F – histological section of idem. G – long choanosomal spicules. H – small ectosomal spicules. Scale bars: A – F 2 mm; G – H 0.1 mm.