(Bowerbank, 1858)
Species Overview
Aphroceras ensata (Bowerbank, 1858) is a tubular white sponge with optically smooth surface. The tube opening has a "naked" rim. It is similar in appearance to Sycon spp. (but these have a rugose surface and a crown of long spicules), Grantia compressa (but this is flattened), and Leuconia fistulosa (but this is likewise rugose). A species with which it may be confused easily is the rare Ute gladiata , from which it differs only in microscopical details. It is fairly common on the south coasts of the British Isles and along the coasts of France.
Taxonomic Description
Colour: White.
Shape, size, surface and consistency: Tubular, elongately oval, sometimes with a short stalk. Length up to 2 cm, diameter about 5 mm. Apical oscule with a naked rim. Surface optically smooth. Consistency fragile.
Spicules: Calcareous. (Aphroceras ensata spics)
Ectosomal and choaonosomal triactines similar, regular, with rays 70-400 x 5-13 µm; triactines of the subatrial skeleton sagittal, with paired rays 70-90 x 6-8 µm and unpaired (basal) rays 100-240 x 6-8 µm; triactines of atrial skeleton sagittal, with paired rays 50-150 x 5-8 µm and unpaired ray 100-250 x 5-8 µm.
Tetractines of the subatrial skeleton, similar to triactines, but with apical ray 120-200 x 7 µm; atrial tetractines similar to triactines, but with long apical ray of up to 450 x 20;
Long ectosomal oxeas: 1000-3000 x up to 160 µm; microdiactines 70-250 x 5 µm.
Skeleton: (Aphroceras ensata skel) Nominal specimens have a leuconoid structure, but specimens of the forma syconoides have a sycon structure. Ectosomal layer of longitudinally arranged long oxeas is normally present but may be absent in forma impressa . Usually there is a layer of ectosomal or subectosomal triactines present and microdiactines are perpendicular to the surface (Aphroceras ensata detail). Choanosomal skeleton formed by the paired rays of the sagittal triactines and a tangential layer consisting of sagittal tetractines and regular triactines. Atrial skeleton consists of a row of triactines and the basal rays of the subatrial triactines sticking far into the atrial cavity.
Reproduction: July-August.
Ecology: Intertidal caves, and on rocks in the sublittoral.
Distribution: Norway, British Isles, Roscoff.
Etymology: Ensata (Latin) = sheathed, referring to the surface cover of long tangential oxeas.
Type specimen information: The type is in the Natural History Museum, London: BMNH 1955.1.2.106 (dry + slides) (Bk. 885).
Remarks
The habit is shared with several other Calcarea and they may be confused with the present species unless microscopic examination is made. There is apparently a large variation in structure (syconoid and leuconoid) and spicule categories (variable presence of large ectosomal oxeas). Borojevic considered these variants as formas syconoides Borojevic, 1967 and impressa Hanitsch, 1890. Burton's (1963) summary description shows many discrepancies with Borojevic's (1967) description.
Source: Borojevic, 1967.