Hymedesmia stellifera Goodwin & Picton, 2009

Order : POECILOSCLERIDA

Family : Hymedesmiidae


Form: Bright yellow/orange sponge forming large patches (over 20 cm in diameter), which are very conspicuous because of their bright colour and oscule form.

Apertures: Prominent oscules surrounded by numerous (1020) oscular channels, some of which are branched. The oscules are regularly spread over the sponge surface, and are arranged in diamonds. The ends of the oscular channels touch those of neighbouring oscules, giving the surface a regular star-type pattern.



Internal characters

Skeleton: Basal layer of large and small acanthostyles, from which ectosomal spicules arise in columns that are 1015 spicules thick. The smaller acanthostyles are more abundant. Sigmas are very abundant throughout the tissue. Chelae are present in certain regions of the sponge, but may not be apparent in some specimens. Where present, they are reasonably common and form a layer at the suface. The sponge is ~800 mm thick.

Spicules: Large acanthostyles: 265440 μm (358 μm) by 812 μm. These are fusiform acanthostyles with a tylote head. The shaft is smooth, and the head is sparsely spined with small, rounded spines. Occasional spicules are present, consisting of two of these acanthostyles fused at the head. Small acanthostyles: 6595 μm (79 μm) by 810 μm. These acanthostyles are very characteristic in appearance; they taper evenly to a sharp point, with no development of the head. The majority of the shaft is spined with large spines, but the last eighth to one-quarter, towards the tip, is smooth, and there are smooth areas on the shaft above the head. Ectosomal spicules: styles which are 210290 μm (247 μm) in length, with the majority of being 810 μm wide, but with some much thinner spicules of 35 μm in width. These spicules are fusiform: one end is rounded and tylote, and the other end is pointed; some are mucronate at the tip. Sigmata: 1012 μm in length. Chelae: 1518 μm in length. These are small chelae, with leaf-like alae, and are only joined to the shaft by a short section at the top. The alae have a claw-like appearance when viewed under the light microscope.


Distribution: Currently only known from Rathlin Island and the Maidens in the North Channel and Loch Sunart and Lunga in western Scotland.

Identity:

Editors: Claire Goodwin & Bernard Picton.



 Picton, B.E., Morrow, C.C. & van Soest, R.W.B., 2011. [In] Sponges of Britain and Ireland
http://www.habitas.org.uk/marinelife/sponge_guide/sponges.asp?item=C6630

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