Oceanapia isodictyiformis (Carter, 1882)

Order : HAPLOSCLERIDA

Family : Phloeodictyidae

Form: Oceanapia isodictyiformis forms a basal mass from which long dirty white-brown fistules with paper thin walls stick out. It is very fragile and partly buried in the sediment in the shallow sublittoral. Only four records of this apparently rare species are known.

Colour: The colour alive is fawn (Carter, 1882); ZMA specimens (in alcohol) are white.

Consistency: fragile

Surface: The holotype consists of a firm piece of agglomerated shell-detritus, 4.5 x 2.5 x 2 cm, completely overgrown by and intermixed with the body of the sponge. At the surface of the sponge there are numerous partly broken-off, very fragile fistules. They are 1-2 mm in diameter and 15 mm long. ZMA POR. 5792 consists of a basal part of 7 mm in diameter from which one fistule, 2 cm long and 2 mm thick arises. Some small shell fragments are incorporated into the basal part. ZMA POR. 5794 consists of small fistules attached to some minute body fragments. Surface: even. Corriero's (1989) specimen from Sicily has longer fistules grouped close together.

Internal characters

Skeleton: The ectosomal skeleton of the body is a regular, unilayered reticulation of intercrossing oxeas, which are bound by a little amount of spongin at the nodes. The fistules are composed of longitudinal pauci-to multispicular tracts, with the interstices completely filled with a rather dense, isotropic reticulation of single spicules. The choanosomal skeleton consists of a dense reticulation of multispicular tracts, and a rather dense, subisotropic reticulation of single spicules Iying in between the tracts. Spongin sparse, nodal.

Spicules: Slightly curved oxeas, evenly tapering towards a sharp point: 120-142-160 x 4-7-10 μm.

Habitat: Shallow water, growing on shell-detritus on the seabed and on the undersides of stones.

Distribution: SW Ireland (specimens ZMA collection, 12 m), Atlantic coast of Spain (Carter, 1882, shallow-water); Tenerife (specimen ZMA collection, shallow-water); Mediterranean (Corriero, 1989).

Distribution Map: NBN map : National Biodiversity Network mapping facility, data for UK.

Identity: Carter's original material and the specimens in the ZMA collection conform in every respect to Phloeodictyon nodosa, as described by George and Wilson (1919: 152) and Van Soest (1980, as Pellina nodosa) from the Western Atlantic. O. isodictyiformis is a very distinctive species characterized by its skeletal architecture and its ability to incorporate shell-detritus and grains into the body, and it is therefore surprising that there are only few Atlantic records of the species. The Irish records are the first North Atlantic records since Carter's description of the species. It might have been overlooked because of its cryptic habit but this seems unlikely. O. isodictyiformis is a rare species.

Editors: Christine Morrow, Bernard Picton & Rob van Soest.