Topsentia Berg 1899

Kefalas, Efthimios & Castritsi-Catharios, Jeanne, 2012, A new species of Halichondriidae, Topsentia vaceleti n. sp. (Halichondrida, Demospongiae, Porifera), collected from coralligenous bottoms of the Aegean Sea, Zootaxa 3314, pp. 58-68 : 59-64

Genus Topsentia Berg 1899

Type species: Anisoxya glabra Topsent, 1898: 234 (by original designation).

Diagnosis. Halichondriidae of massive amorphous to lobate shape, with brittle and rough texture. Ectosomal skeleton consisting of a crust-like partly tangential or paratangential arrangement of small spicules grading into the densely confused choanosomal skeleton of larger spicules. Choanosome skeleton lacks spongin fibres and little collagen as a consequence spicules show a confused, directionless and packed arrangement around canals, cavities, etc. Smaller spicules concentrated at the surface, usually arranged without any order, produce a compact, paratangential, ectosomal layer, creating a microhispid surface. Spiculation consists of oxeas in a wide size range, with two or three size classes distinguished. Twisted, bent and double-bent spicules sometimes present. No raphide microscleres (according to Erpenbeck & Van Soest 2002, partly emended by Ilan et al. 2004).

Τ opsentia vaceleti n. sp. Figs 1–8 , Table 1

Holotype: ZMUA 408. Island Fourni, Greece, Aegean Sea, 37.5347o N, 26.3861o E, 70 m depth, coralligenous substrate ( Fig. 1 ).

Etymology. Named in honor of Prof. Dr. Jean Vacelet, one of the most brilliant spongologists.

Description. Shape. The sponge is massive, almost spherical, with a diameter of 8cm. Its surface is smooth with a few smooth and deep grooves ( Fig. 2).

Texture. Sponge is moderately hard practically incompressible, brittle, with the fragile structure of its skeleton destroyed when compressed.

Oscules. Few (less than a dozen counted in the entire sample), generally small (<1mm) and hard to see.

Color. Grey-white when harvested, remains stable when immersed and kept in ethanol.

Spicules. The spicules are oxeas with a wide range of sizes, (Figs 4a–b & 5) clearly divided into two categories. The principal category of oxeas is of intermediate size and relatively thick, found in considerable numbers (over 90% of the total number of spicules) in any spicule preparation taken from any part of the sponge body. Spicules are slightly bent at the centre, sometimes double bent or even flexuous, with symmetrical ends and sharp or occasionally stepped or mucronate tips. Measurements: 250–(546)–710 μm long and 3–(8.7)–15 μm wide. The main spicules exhibit a range of sizes but are hardly distinguishable in size classes.

The second category of oxeas ( Fig. 5 ) is evidently longer and thinner, slightly bent at the center; more often double bent or even flexuous or twisted, with symmetrical ends and very sharp tips. Measurements: 960–(1446)– 1980 μm long and 2–(4.7)–8 μm wide.

Statistical analysis of the two spicule categories based on the z-score test ( Zar, 1999), showed that the difference in the length and the relative width (Width/Length *100) of more than 100 spicules, is in both cases statistically significant (respectively z L>2 and z RW>2, p=0.05) (Table 1). Microscleres absent.

Skeleton. The ectosome appears to be hispid from the protruding paratangential surface spicules, single ( Figs 3 & 6) or in tracts and bifurcating at the ends ( Fig. 6). The tangential component of the ectosome consists of a layer of single or few spicules ( Figs 6 & 7 ) and supported by a collagenous membrane ( Fig. 6), which is hardly detachable, and if detached it is separated in flakes ( Fig. 6). Below the ectosome extensive cavities with diameter ranging between 80 and 600 μm were observed ( Fig. 6). The choanosomal skeleton is formed by totally disordered oxeas also possessing vast choanosomal cavities (Fg. 8). These exhibit significant differences against those out of the ectosome, with diameter ranging between 100 and 500 μm. The spongin is minimal and only weakly binds the spicules into tracts, with diameters ranging from 50 to 120 μm.

Distribution. Found only in Furni island, north of the straights between Ikaria and Samos islands.

Ecological data. Harvested on deep coralligenous substrate, at a depth of approximately 70m.

Figures

FIGURE 1. Map of the sampling area and details of the sampling point (marked with *), close to Furni Island (Aegean Sea, Eastern Mediterranean)

FIGURE 3. SEM image of the collageonous ectosome, with the tip of a principal spicule protruding from it. FIGURE 4. A: SEM image of principal spicules. B: SEM image of principal spicules.

FIGURE 5. Topsentia vaceleti n. sp., spicule preparation, showing main category-large (ML) and small (MS) oxeas, and secondary category-long oxeas (LS). (Scale bar: 110 μm).

FIGURE 7. An ectosome flake, with tangentially arranged spicules shown. (Scale bar: 80 μm).