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(Bowerbank, 1866)

Species Overview

Poecillastra compressa (Bowerbank, 1866) is a whitish or yellowish laterally flattened massive or cup-shaped sponge with its oscules concentrated on one of the two sides. It has a friable to hard consistency. It occurs in deep water.

Taxonomic Description

Colour: White or yellowish.
Shape, size, surface and consistency: (Normania crassa) (Ecionemia compressa) (Hymeniacidon placentula) Laterally flattened masses, leaf-or cup-shaped, with oscules and pores on opposite sides. Size up to 8 cm high, 15 cm in lateral expansion, with sides up to 2 cm in thickness. Surface more or less smooth. Oscules up to 3 mm in diameter. Consistency friable but hard.
Spicules: Megascleres: Oxeas: 1375-1900 x 16-45 µm; orthotriaenes passing into calthropses, very irregularly shaped, rays 170-320 x 20-25 µm.
Microscleres: Spined microxeas, centrotylote: 80-200 x 3 µm; spirasters with spined rays: 28-33 µm; amphiasters with thin, spined rays: 20-26 µm.
Skeleton: Ectosomal skeleton a thin crust of microscleres supported by tangential intercrossing oxeas, carried by a layer of orthotriaenes/calthropses. Choanosomal skeleton a confused mass of oxeas.
Ecology: On overhangs and on dead corals, from 12-1300 m.
Distribution: Norway, Shetlands, Hebrides, Rockall, SW Ireland, W France; Mediterranean.
Etymology: The name refers to the laterally flattened shape.
Type specimen information: The type is in the Natural History Museum, London.

Remarks

There is a second species of Poecillastra in the area, viz. P. armata described by Hanitsch (1895) from the West coast of Portugal. It differs from P. compressa in the growth form (10 x 5 x 5 cm) and in the possession of anatriaenes. It is not treated here since no illustrations of habit or spicules of this form are available.
Source: Topsent, 1894.

Poecillastra compressa