Hymedesmia crami 


Family : Hymedesmiidae

Form: Thin, cream incrustation on boulder, with a maximum diameter of 5 cm. There are no obvious pore sieves, and the surface appears slightly hispid and is covered in a thin layer of silt.

Internal characters

Skeleton: Basal layer of acanthostyles, sparsely distributed, with a roughly even ratio of large to small acanthostyles. There are ascending columns of ectosomal spicules that are 10–15 spicules thick, which fan out towards the surface, and may adjoin with adjacent columns. The sponge is 900–1000 μm thick.

Spicules: Large acanthostyles: 370–550 μm (436 μm) by 12–18 μm. Head, very slightly tylote; shaft, mainly smooth, with the bottom eighth to one-quarter covered in very small spines, giving it a roughened appearance. The spines on the head may be rounded at the tip. Small acanthostyles: 105–175 μm (136 μm) by 12–14 μm; the head is not tylote, and is entirely spined with recurved spines, the size of which vary between individual spicules (small–large). In some spicules the spines on the head are larger, and may have rounded tips. Ectosomal spicules: 290–400 μm (360 μm) by 4–7 μm. These are strongyles in which usually one or both ends are tylote. Microscleres: absent.

Habitat: Known only from two specimens, on large stable boulder in tidal stream, 25m depth.

Identity: This sponge had no characters which would facilitate in situ recognition.

Editors: Claire Goodwin & Bernard Picton.

 Picton, B.E., Morrow, C.C. & van Soest, R.W.B., 2011. [In] Sponges of Britain and Ireland