Family MYXILLIDAE subfamily MYXILLINAE
Synonyms Dendoryx incrustans (Johnston, 1842:122) Gray, 1867:535
Form A thick, spreading cushion, with raised ridges. Photographs Friar Is., Connemara. (B.E. Picton)
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.
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.
a
b c
SPECIES DESCRIPTIONS
Spicules The megascleres of the main skeleton are acanthostyles (a) 145-(170)-200μm. The ectosomal spicules are tornotes (b) with spear-shaped, microspined, ends, which are occasionally unequal 180-(190)-200μm. These lie in vertical brushes. Microscleres are spatuliferous anchorate chelae of two sizes, (c) 40μm and (d) 18μm, and sigmata (e) of two sizes, 33μm and 15μm.
Voucher BELUM : Mc564. Malin Beg, Donegal. 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.
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. Breeding Embryos are commonly found in specimens of M. incrustans during the
months of August and September. These are globular, measuring 0.3mm to 0.5 mm (largest diameter).
References Arndt, 1935, p.58.
Hiscock, Stone and George, 1983[1984], p.27.
Sources J.D. Guiterman, S.M. Stone. Editors J.D. Guiterman, D. Moss, B.E. Picton.
Myxilla fimbriata (Bowerbank, 1864:251)
*Family MYXILLIDAE, subfamily MYXILLINAE.
Synonyms Isodictya fimbriata Bwk. 1864:251, Isodictya lurida Bwk. 1866:336.
Form Cushion usually 6-7mm thick; can be 30mm thick. Found as distinct specimens 2-5cm across, with an irregular outline. The specimens are rounded in cross section with steep sides.
Photographs 1. Keem Bay, Achill Island, Mayo.
Colour Bright orange in surface layers, yellow in deeper layers. Specimens from less clear water conditions may be beige in colour. The sponge goes black or brown in alcohol, staining the label, but may fade to a dirty, pale brown.
Smell Slight. Slime None.
Consistency Quite firm, tears easily. “Resilient.”
a
b
c
d
Surface Not ‘open’ as in M. incrustans though underlying porous areas are clearly visible through transparent ‘skin’. “Slightly hispid”, smooth to touch.
Apertures The oscules are small, with slightly raised transparent rims. They are placed towards the central, thickest parts of the sponge, or raised on ridges. There are no oscular channels.
Contraction Slight.
Skeleton The reticulation of multispicular fibres is less regular and isodictyal than in other Myxilla spp. There are no echinating spicules associated with these fibres. Special ectosomal spicules (tornotes) are present. Spongin is scarce.
Spicules The megascleres of the main skeleton are long, sparsely-spined acanthostyles (a) 265-(300)-350μm in length. The surface tornotes (b) measure 202-(290)-325μm in length and have abruptly terminating ends, ending in a short point, often mucronate. The ends are sometimes slightly unequal lying in vertical brushes. Different development stages of tornote ends can be present in any one specimen, making recognition difficult. However the broad pattern should conform to the diagram given here. Microscleres are spatuliferous anchorate chelae, of two sizes (c) 60μm and (d) 27μm. Sigmata are infrequent or absent, thin, and easily overlooked. Voucher BELUM : Mc575. Skird Rocks, Galway.
Habitat On rock in lower infralittoral and upper circalittoral.
Distribution “Arctic; Faroes; Norway; Sweden; British Isles!” Known recently from various sites on the W and SE of Ireland, where this sponge is a characteristic circalittoral species in sites exposed to the Atlantic. Also Rathlin Is., Co. Antrim; St. Abbs; Coll; Lewis.
Identity Superficially there might be confusion with Amphilectus fucorum but there are distinct spicule differences. The blackening of the sponge in alcohol is rapid and striking, and this combined with a lack of slime in what is otherwise a typical Myxillid skeleton makes this species distinctive from other Myxillid species such as M.
rosacea and M. incrustans. If there are echinating spicules and the chelae are arcuate, the specimen belongs
to a different genus, e.g. Ectyodoryx. Note from BEP: “There is definitely another form/species of this sponge with distinct oscular channels, which goes dark brown in alcohol, doesn’t slime and has a similar spiculation. However the acanthostyles in this form are much thicker.”
References Arndt, 1935, p.58.
Bowerbank 1866, p.337; 1874, p.147.
Sources B.E. Picton, S.M. Stone, R. Earll. Editors R. Earll, D. Moss, B.E. Picton.
Myxilla rosacea (Lieberkuhn, 1859:521)
*Family MYXILLIDAE Synonyms None in common use.
Form Cushions 0.5 - 1cm thick, forming patches up to 15cm across; becoming branched - erect in deeper waters. It may form upright growths around hydroid stems.
Photographs BELUM: Mc1847. E. Tearaght Is., Blaskets, Kerry.
Colour Yellow, or “dirty rose-red”, or brownish orange when alive.
Smell None.
Slime. Considerable quantities are exuded. Consistency “Loose, somewhat crumbly. Elastic.”
a
b d
SPECIES DESCRIPTIONS
Surface A loose, porous appearance, similar to that of M. incrustans. Slightly hispid.
Apertures The oscules are scattered across the animal, and have raised edges. Exhalant channels run up to the oscules; “not apparent when preserved”.
Contraction None.
Skeleton The main skeleton is a reticulation (sub-isodictyal) of acanthostyles in multispicular fibres, with no echinating spicules. Special ectosomal spicules (tornotes) are present. Spongin is scarce.
Spicules The megascleres of the main skeleton are acanthostyles (a) whose spines are few but strong, and present throughout the length of the spicule 140-(145)-152μm . The surface tornotes (b) bear three or four small spines at the ends and are 140-(150)-160μm long, and lie in vertical brushes at the surface. The microscleres are spatuliferous anchorate chelae (c) of two sizes (12-15μm, 20- 25μm), which are present throughout the sponge, together with small sigmata (d), ca. 17-35μm.
Distribution “Arctic; Faroes; British Isles; Atlantic coasts of France and Spain; Mediterranean; etc.” Widely distributed and common on the western coasts of the British Isles.
Identity Superficially it can be very similar to M. incrustans, but it does not seem to form the raised, oscule bearing ridges of the latter species (?). Examination of the tornote ends at high power is necessary to confirm identification. It is possible that more than one species is involved here.
Voucher BELUM : Mc1010. St Kilda.
Habitat At exposed sites, on rock, from the infralittoral “down to 300 m, and on shells”. Also found on the shore. References Arndt, 1935, p.59
Hiscock, Stone and George, 1983[1984], p.27.
Sources B.E. Picton, S.M. Stone. Editors D. Moss, B.E. Picton.