(Cabioch, 1968)
Species Overview
Clathria (Microciona) ascendens (Cabioch, 1968) is one of the numerous red encrusting microcionids, which can only be reliably identified from microscopic preparations. The distinctive feature of this species is that it has oxeas among the normal complement of (acantho-)styles. So far this species is only known from a few records from the Atlantic coasts of France and Spain.
Taxonomic Description
Colour: Red.
Shape, size, surface and consistency: Encrusting, reaching a thickness of 3 mm. Surface finely conulose, hispid.
Spicules: Megascleres : Ectosomal subtylostyles, straight or slightly curved, with smooth heads: 130-210 x 2-4 µm; large acanthostyles, straight or slightly curved, smooth except for a few small spines at the head, and sometimes near the point: 100-240 x 5-10 µm; oxeas, probably malformed large acanthostyles because they occupy the same position in the skeleton, often slightly angulated or centrotylote, the points bearing often a few spines: 145-290 x 4-7 µm; echinating acanthostyles, straight and spined all over with fine spines: 55-105 x 3-7 µm; echinating acanthoxeas, probably malformed echinating acanthostyles, straight or angulated, often a bit centrotylote: 80-110 x 3-4.5 µm.
Microscleres : Palmate isochelas, rather rare: 13-15 µm; toxas, almost straight or very slightly incurved, with a very small and often twisted median bend, entirely smooth: 180-430 x 1-1.5 µm.
Skeleton: The ectosomal skeleton is rather independent of that of the choanosome and consists of a confused mass of subtylostyles, which are also distributed towards the interior. The choanosomal skeleton consists of long spicule tracts bound by ample spongin, 30-80 µm in diameter; they rise up from a basal plate of spongin. The tracts consist of large smooth (acantho-) styles and are echinated by smaller entirely spined acanthostyles. The basal plate is echinated by two size categories of acanthostyles: large smooth styles and small entirely spined acanthostyles. Towards the surface the spicule tracts branch off and diverge and become rather confused. Oxeas of two sizes are intermingled among the styles and do not have a special localization.
Ecology: Among Laminaria in more exposed localities.
Distribution: So far only recorded from Bretagne and Galicia.
Etymology: The name refers to the long ascending skeletal columns.
Type specimen information: The type is in the collections of the Station Biologique of Roscoff.
Remarks
The oxeote modifications are the major distinguishing feature of this species. Only Mediterranean Antho oxeifera (Ferrer-Hernandez, 1921 as Clathria ) has similar oxeotes, but skeletal architecture and form and size of the toxas of that species are clearly different (cf. redescription of Uriz and Maldonado, 1993). The toxas of C . ascendens remind of C . strepsitoxa (Hope, 1889), but this species lacks the oxeotes, has a second smaller category of toxas, and clearly longer and thicker megascleres.
Source: Cabioch, 1968.