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Howson & Chambers, 1999

Species Overview

Ophlitaspongia kildensis Howson & Chambers (1999) is a red crust with bumpy surface characterized by a reticulate spongin fibre skeleton and spiculation of Microcionidae, but lacking echinating acanthostyles or chelae. From the sympatric, closely related Ophlitaspongia papilla (Bowerbank) it differs in having a more irregular skeleton and longer spicules. O. papilla has two size classe of toxas, whereas the present species has only one.

Taxonomic Description

Colour: The sponge is orange-red in colour.
Shape, size, surface and consistency: The crust is thin, 1-3 mm deep, with a firm, crumbly and compressible texture, and does not contract on collection. The surface is irregular, with numerous knob-like projections and distinctly hispid; it is obviously porous with numerous pores and oscules of various sizes. There are few channels present. No reported odour.
Spicules: There are four classes of spicules including two size-classes of subtylostyles, one size-class of styles and one size-class of toxa. The subtylostyles span a large size range from 103 to 667 µm in length, with no visually obvious division into size-classes. However, an analysis of 143 measurements combined from three specimens using probability paper showed that the spicules clearly fall into two size-classes: (1) those < 200 µm; (2) those >200 µm. These two classes correspond approximately to the spicules in the ascending columns (the longer spicules) and those lying perpendicular to the columns (the shorter spicules). Although there is considerable overlap in the sizes of these two structural groups, the spicules have been divided below on this basis.
Megascleres. (1) Principal skeletal spicules: long subtylostyles with a wide range of lengths; some have a more pronounced knob-like end than others and many are curved. Size range: 183-320-564 µm.(2) Secondary skeletal spicules: short fat subtylostyles ranging in shape from
straight to curved. Size range: 111-162-287 µm. 3) Auxiliary spicules: long thin subtylostyles. Size range: 262-407-548 µm.
Microscleres. (4) Toxas with smooth tips. Size range: 48-86-135 µm
Skeleton: Ectosome: hispid, a reticulate layer of spongin with bundles of subtylostyles projecting through the surface at the head of ascending ¢bres. Spongin skeleton: spongin fibres with a distinctive but irregular reticulate pattern of fan-shaped ascending primary fibres and irregular secondary fibres arising from a single basal layer of spongin. Mineral skeleton: plumose ascending columns of large smooth subtylostyles, aligned with the rounded ends towards the base of the sponge are present and core the vertical spongin fibres. The plumose columns have shorter, smooth subtylostyles projecting through the ascending fibres some of which lie perpendicular to and between ascending ¢bres. Bundles of auxiliary, thin subtylostyles are scattered throughout the sponge. Toxas are abundant and scattered throughout the spongin fibres.
Ecology: This is a sublittoral species which has been recorded from exposed circalittoral bedrock between depths of 15 and 50m. The majority of specimens so far collected have been from rock faces in offshore locations, in wave-exposed conditions. The nudibranch Rosttanga rubra has been found on individuals of Ophlitaspongia kildensis at several locations.
Distribution: Currently known only from western coasts of the British Isles (Scotland, Ireland).
Etymology: The specific epithet refers to the St Kilda archipelago which is the type locality of the species.
Type specimen information: Several pieces of crust from St Kilda, Western Isles, Scotland: 57°52.71'N 08°29.55'W, 20-50 m, 17 July 1984, collected by C.M. Howson, Ulster Museum BEL Mc 1007 which were designated as the holotype

Remarks

The generic placement of Ophlitaspongia kildensis is based on the skeletal arrangement and spicule complement. However, spicule sizes, detailed skeletal structure, the general appearance of the living material and habitat all distinguish the new species from the other known north-east Atlantic species O. papilla. The only other similar species described from the north-east Atlantic is Clathria (Microciona) basifxa (Topsent, 1913) from northern Norway from a small (< 1 cm2) specimen on a very irregular piece of stone. This material was assigned to Ophlitaspongia by Howson & Chambers (1999). The reported type material from the Musée Océanographique in Monaco could not be found. The description of the specimen includes spicule measurements and drawings which are not diagnostic; there is no illustration of the skeletal structure. Although the sizes of the spicules correspond with three of the spicule classes in Ophlitaspongia kildensis, the latter is distinguished by the presence of two classes of principal subtylostyles. The lack of a figured skeleton and details of the position of spicules has prevented a comparison of this distinctive feature. The only known subsequent material of C. basifxa was collected from Lille Sotra and Marsteinsboen, Norway, from a depth of 100-150 m (van Soest & Stone, 1986). These specimens cannot be located at the Copenhagen Museum; however, a sponge scraping which shows the spicule complement was made available (R. van Soest). We know of no other records of this species for a thorough comparison. A comparison of the spicule sizes and other material indicates that basifxa and kildensis are separate species.
Source: Howson & Chambers, 1999.

Ophlitaspongia kildensis