Clathria (Microciona) ctenichela (Alander, 1942) is a thin red crust growing on dead deep-water corals in the fjords of Sweden and Norway. Its microscopic characters are very similar to those of the sympatric C. elliptichela but it lacks the characteristic cleistochelae of that species. Further research may prove these two forms conspecific.
Colour: Light grey to red.
Shape, size, surface and consistency: Thinly encrusting; hispid, due to projecting spicules. Consistency loose and cavernous, soft, crumbly.
Spicules: Megascleres: Ectosomal subtylostyles with microspined apices: 340-650 x 4-7 µm; choanosomal (acantho-)styles, shaft bent, smooth, head barely swollen, bearing conical spines: 665-900 x 8-18 µm; echinating acanthostyles, entirely spined: 95-160 x 5.5-9 µm.
Microscleres: Palmate isochelae with the inner side of the shaft provided with a comb-like outgrowth ("crista"): 12-15 µm; toxas, in two size categories, large: 45-265 µm, and small: 6-12 µm.
Skeleton: Leptoclathriid or hymedesmoid, i.e. with choanosomal styles singly or in groups of four or five erect on the substrate, surrounded by echinating acanthostyles. The ectosomal subtylostyles form bouquets at the surface, supported by the choanosomal styles. Subtylostyles are also strewn tangentially.
Ecology: Encrusting dead Lophelia branches at 85-100 m.
Distribution: Sweden, Norway (fjord areas).
Etymology: ctena (Latin) = comb, referring to the shape of the chelae.
Type specimen information: No data.
Only the absence of cleistochelae distinguishes this species from the sympatric Clathria (Microciona) elliptichela. If the chela condition is found to be variable in this species, they may be synonymized. For the time being it seems prudent to uphold them as separate species.
Sources: Alander, 1942; Van Soest and Stone, 1986.