Myxilla incrustans (Johnston, 1842)


Family : Myxillidae

Form: A thick, spreading cushion, with raised ridges.

Colour: Usually sulphur yellow.

Smell: None. Slime : Exudes a large amount of slime when taken out of the water.

Consistency: Moderately soft, elastic, crumbly.

Surface: Distinctive, consisting of numerous deep labyrinthine channels, across which run cobweb - like strands of tissue.

Apertures: Oscules are variable in size, numerous and scattered. They are obvious, circular and typically in lines along the raised ridges.

Contraction: Not noticeable.

Internal characters

Skeleton: A regular, isodictyal, reticulation with multi-spicular fibres, without echinating spicules. There is a surface layer of tornotes, tangential or at an angle to the surface. Spongin is scarce.

Spicules: The megascleres of the main skeleton are acanthostyles (a) 145-(170)-200Ám. The ectosomal spicules are tornotes (b) with spear-shaped, microspined, ends, which are occasionally unequal 180-(190)-200Ám. These lie in vertical brushes. Microscleres are spatuliferous anchorate chelae of two sizes, (c) 40Ám and (d) 18Ám, and sigmata (e) of two sizes, 33Ám and 15Ám.

Habitat: On rock in clear water. "LW to 400m on stones, shells, sand and mud."

Distribution: "Arctic; Atlantic coasts of Europe south to Gibraltar; Mediterranean, etc." Recently known from many sites around the British Isles.

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

Identity: This is probably the commonest massive, yellow sponge in exposed sites on vertical or clean rock. Initially identification needs to be checked with a microscope. Having checked that it is Myxilla (with a network of acanthostyles, without echinating spicules, accompanied by spatuliferous anchorate isochelae, and with tornotes at the surface), it is necessary to examine the tornote ends (b) with a microscope lens of good resolution (x40 objective is adequate). A number of spicules may have to be examined before it can be decided unambiguously which type is present.

Voucher: BELUM : Mc564. Malin Beg, Donegal.

Editors: J.D. Guiterman, D. Moss, B.E. Picton.

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