Clathria (Thalysias) collosclera, Van, Rob W. M., 2009

Van, Rob W. M., 2009, New sciophilous sponges from the Caribbean (Porifera: Demospongiae), Zootaxa 2107, pp. 1-40 : 16-18

Clathria (Thalysias) collosclera n. sp.

( Figs 6 A–I)

Holotype. ZMA POR. 16880, Curaçao, in front of Carmabi, 12.124°N - 68.975°W, reef cavities at approx. 10 m, 10-2001, coll. S.Scheffers, # 18.

Paratype. ZMA POR. 16881, Curaçao, in front of Carmabi, 12.124°N - 68.975°W, reef cavities at approx. 10 m, 10-2001, coll. S.Scheffers # 19.

Description. Thinly encrusting sponge, size of holotype 5 x 8 x 1–2 mm, paratype even smaller. It was found growing in the interstices of encrusting coralline algae and bryozans without forming large patches. Color red alive, beige in alcohol. Surface microhispid, consistency very soft, easily damaged.

Skeleton. Plumose with discrete spicular columns rising up from a basal spongin plate on the substrate and fanning out at the surface in characteristic bouquets. Columns consist, from the substrate upwards successively of 3–5 principal styles, recognizable as the longest and thickest of the megascleres, gradually replaced by 10 or more auxiliary subectosomal subtylostyles, which in turn carry the surface bouquets of smaller ectosomal subtylostyles. The base of the columns is echinated by small auxiliary acanthostyles. Colloscleres are densely distributed throughout the choanosome and the ectosomal region, without distinct concentrations.

Spicules. Choanosomal principal styles, two categories of auxiliary ectosomal subtylostyles, echinating acanthostyles, toxas, colloscleres, no proper chelae.

Principal styles ( Figs 6 A–B), entirely smooth, somewhat fusiform (the rounded end less thick than the upper part of the shaft), sharply and gradually pointed, 237- 320.7 -423 x 3 - 4.8 -7 µm. Subectosomal larger auxiliary subtylostyles (Figs C–D), entirely smooth, thin, with faintly swollen head, 219- 244.5 -303 x 2 - 2.3 -3 µm, and ectosomal small auxiliary subtylostyles ( Figs 6 E–F), entirely smooth, thin, with faintly swollen head, 96- 113.3 -156 x 0.5- 1.0 -1.5 µm. Echinating acanthostyles 42- 52.1 - 66 x 3.5- 4.4 -5 µm.

Microscleres toxas ( Fig. 6 H), bow-shaped, shallow-curved, fairly thick, entirely smooth, not abundant, 92- 106.8 -126 µm, and bean-shaped colloscleres ( Fig. 6 I), hollow, faintly reminiscent of chela-shape but no clear alae or shaft can be detected, surface appears smooth under the light microscope, but is slightly wrinkled under SEM (possibly artefactual), 11- 12.8 -15 µm; occasionally clusters occur consisting of two, three up to a dozen of colloscleres, possibly artefactual, as they appear to be rare or absent in the teased preparations.

Ecology. Shallow depth, reef cavity dweller, encrusting coralline algae and bryozoans.

Etymology. Named for the peculiar colloscleres.

Remarks. The subgenus Thalysias has seven junior synonyms (cf. Hooper, 2002), among which is Colloclathria Dendy (1922) , a so far monotypical genus erected for a ramose sponge from the Seychelles, Colloclathria ramosa Dendy (1922) , with peculiar 'grain-of-rice' microscleres, among an otherwise typical Clathria (Thalysias) spicule complement and skeleton. Hooper (1996, 2002b) concluded that the peculiar microscleres are derivates of isochelae and assumed they were extremes of a hypertrophied chela-type called 'cleistochelae', in which both frontal alae meet and the shaft extends with a ridge or plate to fill up the space between the alae. Such microscleres are not uncommon in various apparently unrelated Clathria and Mycale species. Because of this and also because Colloclathria so far was monotypical, the species was assigned to Clathria (Thalysias) . The combination Clathria ramosa was already occupied by C. (T.) ramosa ( Kieschnick, 1896 as Rhaphidophlus ), so Hooper (1996) proposed Clathria (Thalysias) amiranteiensis as a replacement name.

The ZMA collections holds three Seychelles samples (ZMA Por. 11890, Seychelles, St. Joseph Atoll, S rim, 5.45°S 53.35°E, 28-12-1992, 10 m, coll. R.W.M. van Soest, SCUBA, Netherlands Indian Ocean Program stat. E-759/01; ZMA Por. 11992, Seychelles, N of Poivre Atoll, 5.7°S 53.3°E, 31-12-1992, 42- 45 m, coll. R.W.M. van Soest, Agassiz-trawl, Netherlands Indian Ocean Program stat. E-776/12; ZMA Por. 10644, Seychelles, W of Poivre Atoll, 5.7667°S 53.1833°E, 01-01-1993, 57 m, coll. R.W.M. van Soest, rectangular dredge, Netherlands Indian Ocean Program stat. E-778/21). I examined these and included Dendy's (1922: 74) description of three samples from the Seychelles /Amirante group and Coetivity, in a comparison with the new species. The Seychelles species can be characterized as repent-ramose, with a tendendy to have the branches undivided or branching only close to the surface. The sponges encrust the substrate of dead corals and from this occasional branches are formed which are partially erect, but tend to follow a tortuous course, ending roundly. Diameter of the branches is 2–5 mm, and length varies from 2 to 14 cm. Color is yellow, orange, or orange-red; in alcohol the branches are light brown. Surface is optically smooth but microhispid, feeling slightly rough. Oscules are not apparent, but encrusting parts have a veinal pattern. Consistency firm, slightly compressible, tough. The ectosomal skeleton is characteristic for Thalysias with surface bouquets of smaller microspined ectosomal styles (approx. 120 x 3 µm), supported subectosomally by larger microspined ectosomal styles (220 x 5 µm). The distribution of the surface bouquets is not very dense, with individual bouquets flaring widely and touching each other’s outer spicules only barely. The ectosomal skeleton is carried by an irregular reticulation of spicule tracts making up the internal skeleton of the branches. Tracts consist of two or three smooth fusiform main styles with rugose or occasionally smooth heads (200 x 15 µm), cemented by light spongin and echinated sparingly by auxiliary acanthostyles (72 x 10 µm). They make rounded or squarish meshes, and leave large open spaces, which are presumably canals. Many megascleres and microscleres are loosely scattered in the interior. Microscleres are toxas (60–120 x 1 µm), palmate isochelae (12–15 µm), and abundant oval or bean-shaped colloscleres of 10–12 µm in length.

From these observations it is obvious that the two sponges discussed here are quite dissimilar in morphology and spiculation: tough branches vs. soft thin crust, microspined ectosomal spicules vs. smooth, presence of true palmate isochelae vs. absence thereof. Nevertheless, the peculiar colloscleres are a compelling synapomorphy for the two species discussed here. It is unclear whether these are truly derivations of the chelae as Dendy (1922) maintained from his observation of 'intermediate forms' drawn rather suggestively by him (pl. 14 fig. 4e). Hooper's (1996) opinion that the colloscleres are cleistochelae is here rejected, because in cleistochelae the frontal alae meet and/or the shaft grows a forward extension, but the obvious derivation from palmate isochelae is never in any doubt with such spicules. In colloscleres the entire spicule - if it is chela-derived - is enveloped in a siliceous thin coat which is dramatically different from a chela developing secondarily infilling of the open space between alae and shaft.

If the colloscleres of both species are to be considered a homologous derived character, then close phylogenetic relationship is the likely assumption, since no other Clathria species with such microscleres are known. Colloclathria may need to be reinstated as a subgenus or a similar infrageneric unit to distinguish these sponges from the bulk of the Clathria (Thalysias) species. Several spicular features of the two sponges support such close affinity: the shape and size of the toxas are quite similar and the size of the ectosomal and choanosomal megascleres is also not dissimilar. Biogeographically, such a taxon would show a disjunct distribution in Indian Ocean and Caribbean reefs, which may be easily explained as a relict Tethyan pattern. So far, no reliable records of C. amiranteiensis in other parts of the Indo-West Pacific are known, so a more widespread Tethyan distribution remains to be demonstrated.

Alternatively, although both C. collosclera n. sp. and C. amiranteiensis belong to the subgenus Thalysias and the colloscleres appear uniquely derived, it is possible that they represent independent developments. Possibly, the colloscleres are an environmentally induced derivate of chelae. This is supported by the occurrence of potentially homologous colloscleres in the enigmatic sponge described as Collosclerophora arenacea Dendy (1917) . The morphological and skeletal features of this South Australian sponge are radically different again from the two above described Clathria(Thalysias) species. The growth form is massive, solid, and the skeleton consists chiefly of sand. The only megascleres present are thin strongyles occurring in plumose bundles among the sand grains. By these characters, this sponge is classified as Chondropsis in the poecilosclerid family Chondropsidae (cf. van Soest, 2002a). The colloscleres are bean-shaped and were demonstrated to be siliceous, but soft-skinned, capable of swelling when water is added to them. This might well conform to the colloscleres of C.(T.) collosclera n. sp. as the surface of many of them appear wrinkled under SEM. Verifying the homology of both types of colloscleres unfortunately is virtually impossible as there is preciously little material left of C. arenacea . There is no rationale for assigning Chondropsis arenacea and Clathria (Thalysias) collosclera – C. (T.) amiranteiensis to a single monophyletic group, as this would violate a large number of convincing skeletal and spicular synapomorphies. If the colloscleres are all of similar build and material, that would surely indicate they have been developed independently, at least in different families.

Figures

FIGURE 6. Clathria (Thalysias) collosclera n. sp., SEM images of spicules (Holotype ZMA Por. 16880). A – B. Choanosomal style and details of head and apex; C – D. Larger subectosomal subtylostyle and details of head and apex; E – F. Small ectosomal subtylostyle and details of head and apex; G. Acanthostyle; H. Toxa; I. Various inividual colloscleres (left) and – possibly artefactual – merged colloscleres.