Coryphella gracilis (Alder & Hancock, 1844)

Author & date of last revision: Ian Smith on 6 August 2012

Synonyms:Eolis smaragdina Alder & Hancock, 1851; Eolis gracilis Alder & Hancock, 1844; Flabellina gracilis (Alder & Hancock, 1844); Coryphella verrucosa smaragdina Thompson & Brown, 1976;

Description

Revised August 2012

synonym: Flabellina gracilis Alder & Hancock, 1844, accepted by WoRMS

Body (excluding appendages)
Usually up to 12mm, occasionally 15mm, long. Semi-transparent white, revealing internal anatomy [image4]. When mature, often at less than 10 mm, opaque white blobs of ovotestis visible [1]. Discontinuous white opaque medial line from the rear cerata to tip of the tail [5].
Cerata
Able to conceal posterior half of body, but dorsum often fully exposed. Arranged in up to 5, occasionally 6, longitudinal groups on each side of the body. Transparent white revealing bright red, orange-red, ginger-brown or green [8] granular internal digestive gland. Subapical narrow band of white surface pigment. Cerata arise from raised notal ridge [7], which is made noticeable by coloured section of digestive gland in it which connects with bases of cerata.
Rhinophores
Smooth, sometimes slightly wrinkled. Translucent white with white surface pigment on distal half [2].
Head
Translucent white oral tentacles [2] with white surface pigment distally. Oral tentacles similar length to rhinophores.
Foot
Anterior variably extended; often into short propodial tentacles [6]. Semi-transparent white sole reveals white ovotestis, other viscera and cerata [3].

Key identification features

Excluding appendages, the only surface pigment on the body is the discontinuous white medial line from the rear cerata to tip of the tail [5].
White subapical ring on cerata is narrow [7].
Mature with visible white opaque ovotestis lobules when less than 10mm [7].
Usually to 12 mm, maximum 15mm, long.
Prominent notal ridge on each side, often with coloured longitudinal section of digestive gland visible below cerata [7].

Similar species

Coryphella lineata (Lovén, 1846)
White lines run along dorsum and sides of body, and the full lengths of the rhinophores and oral tentacles.
Grows to 50mm long.
Coryphella browni, Picton, 1980
Distal white ring on cerata wider than on C. gracilis.
Maximum length usually 30 mm, sometimes 50mm.
Coryphella verrucosa (M. Sars, 1829)
Interrupted white dorsal line on body becomes continuous on tail.
Maximum length 35mm.
Flabellina pellucida (Alder & Hancock, 1843)
White pigment covers distal end, including apex, of cerata.
Maximum length 40mm.

Ecology and behaviour

Offshore and LWS sheltered rocky shores with strong currents, on or near its prey; Eudendrium spp. (EML), Halecium articulosum and Clytia johnstoni (hydroids). Simultaneous hermaphrodite. Spawn looped around prey, or on rock, when it is a spiral line [9], in mid April, May and possibly other months. Veliger larvae drift as plankton before transforming into the adults.

Distribution and status

Iceland to Atlantic coast of France (GBIF map). Widespread around Ireland and Britain, sometimes locally common. Probably under recorded because of its small size and confusion with other Coryphella spp. (UK interactive distribution map).

References and links

Alder, J. & Hancock, A. 1845-1855. A monograph of the British nudibranchiate mollusca. London, Ray Society.
Thompson, T.E. & Brown, G.H. 1984. Biology of opisthobranch molluscs 2. London, Ray Society.

Current taxonomy: World Register of Marine Species (WoRMS)

Irish distribution map & prey organisms:
Picton, B.E. & Morrow, C.C., 2010. Encyclopedia of Marine Life of Britain and Ireland (EML)

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Photo: