01 Coryphella gracilis

Width of slender body is about 10% of its extended length. Cerata are about as long as the body width. 1: buccal mass. 2: distinctive coiled structure.

Length 8 mm. Menai Strait, Wales. April 2011.

Full SPECIES DESCRIPTION BELOW

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Coryphella gracilis (Alder & Hancock, 1844).

 

Current taxonomy: World Register of Marine Species www.marinespecies.org/aphia.php?p=taxdetails&id=139981

Synonyms: Eolis gracilis Alder & Hancock, 1844; Eolis smaragdina Alder & Hancock, 1851; Flabellina gracilis (Alder & Hancock, 1844); Microchlamylla gracilis (Alder & Hancock, 1844); Coryphella rufibranchialis var. clavigera Odhner, 1929; Coryphella verrucosa var. smaragdina (Alder and Hancock, 1851) [in Thompson and Brown (1976)].

 

GLOSSARY BELOW

 

Description

The small body, grows to a usual maximum length of 12 mm, occasionally 15 mm. It is very slender (Alder & Hancock, 1844-1854), more so than other European Coryphella spp. (Korshunova et al., 2017). Its width is about 10% of its extended length fig. 01 flic.kr/p/2nsSSZQ & fig. 13 flic.kr/p/2nt2wGQ . It is semi-transparent white, revealing the internal anatomy fig. 03 flic.kr/p/2nt1iVM, including a distinctive coiled part of the reproductive system fig. 01 flic.kr/p/2nsSSZQ & fig. 02 flic.kr/p/2nt2x3Q . It matures when about 8 mm long, when the opaque white spheroids of the ovotestes are visible fig. 03 flic.kr/p/2nt1iVM . On the tail there is a discontinuous, opaque white, medial line which is sometimes reduced to a few small spots fig. 04 flic.kr/p/2nt2x2c . The hermaphrodite genital opening may protrude from the side below the cerata behind the right rhinophore fig. 05 flic.kr/p/2nt3QtL .

The cerata are about as long as the body width fig. 01 flic.kr/p/2nsSSZQ but are fewer in number and relatively longer on early juveniles fig. 06 flic.kr/p/2nt1iR8 .They are often narrowed at the base and appear elliptical fig. 03 flic.kr/p/2nt1iVM . They are fewer and flex less than the longer cerata of similar species, and leave much of the notum exposed. On each side of the body they are arranged in up to 5, occasionally 6, linear groups. Each group arises from a pronounced notal ridge, which is transparent, colourless so often difficult to discern fig. 07 flic.kr/p/2nsV6KR . The bright red, orange-red, ginger-brown, yellow fig. 06 flic.kr/p/2nt1iR8 , olive-brown fig. 08 flic.kr/p/2nt1iN2 or green fig. 09 flic.kr/p/2nt1krj internal digestive gland is granular fig. 03 flic.kr/p/2nt1iVM . The gland is visible in the transparent cerata and in the notal ridge connecting them fig. 10 flic.kr/p/2nt1iHh . The digestive gland does not occupy the transparent, colourless apical c. 15% of each ceras which contains an oval white cnidosac and has a thin, irregular, opaque white subapical ring on the surface.

The translucent white rhinophores are smooth or slightly wrinkled with white surface pigment on the distal half fig. 08 flic.kr/p/2nt1iN2 . The head has translucent white oral tentacles with white surface pigment distally. They are a similar length to the rhinophores. The outer lips of the mouth are large and prominent fig. 11 flic.kr/p/2nt3Qkj & fig. 12 flic.kr/p/2nt1kjW .

The anterior of the foot is usually rounded and variably extended laterally into short fig. 11 flic.kr/p/2nt3Qkj or long fig. 12 flic.kr/p/2nt1kjW , triangular, propodial tentacles, giving the anterior a crescentic form. When fully extended the propodial tentacles are about as long as the width of the body fig. 12 flic.kr/p/2nt1kjW . The translucent sole reveals spheroid, white ovotestes and other viscera fig. 13 flic.kr/p/2nt2wGQ ; but early juveniles lack ovotestes . When the ovotestes are fully developed they may obscure the view through the sole fig. 14 flic.kr/p/2nsV6wz .

 

 

Key identification features

Coryphella gracilis (Alder and Hancock, 1844)

1) Cerata length about same as body width fig. 01 flic.kr/p/2nsSSZQ ; relatively longer on early juveniles fig. 06 flic.kr/p/2nt1iR8 . Narrowed at base so sometimes elliptical fig. 03 flic.kr/p/2nt1iVM . Arise from a pronounced notal ridge fig. 07 flic.kr/p/2nsV6KR containing the digestive gland under cerata.

2) Digestive gland in cerata is granular fig. 03 flic.kr/p/2nt1iVM , colour varies red, brownish, orange, yellow or green. Narrow, often fragmentary, subterminal opaque white ring on cerata fig. 10 flic.kr/p/2nt1iHh .

3) Opaque white dorsal line on tail is sometimes fragmentary fig. 04 flic.kr/p/2nt2x2c or missing. No line on rest of body. Distinctive, internal, coiled structure fig. 02 flic.kr/p/2nt2x3Q behind rhinophores. White ovotestes are visible fig. 3 when 8 mm long, at which size ovotestes are missing in similar larger species.

4) Distinct triangular, propodial tentacles. When fully extended, length nearly as great as body width fig. 12 flic.kr/p/2nt1kjW .

5) Scattered records around Britain and Ireland. Few or none in southern half of east coast England and north-east Irish Sea.

 

Similar species

Coryphella verrucosa rufibranchialis fig. 15 flic.kr/p/2nt3QbX & fig. 16 flic.kr/p/2nsV6i8 .

1) Cerata as long as the width of the body, and held at varying angles, often across each other.

2) Cerata have a narrow, subterminal, opaque white ring.

3) Continuous white dorsal line on tail, sometimes a broken, white, dorsal line on body.

4) Propodial expansions sometimes form small propodial tentacles.

5) Recorded from Scandinavia, Britain, Bretagne and also Atlantic and Pacific coasts of North America, Bering Sea and Sea of Japan (Thompson and Brown 1984).

[Coryphella verrucosa verrucosa omitted from comparison as it is unlikely to be confused with C. gracilis]

 

Coryphella browni Picton, 1980. fig. 17 flic.kr/p/2nsV6fY & fig. 18 flic.kr/p/2nt2wjA .

1) Cerata length up to twice the body width.

2) Broad white band on cerata distally, but no pigment on apex.

3) Interrupted white medial line, often reduced to a few dots or none, on tail. No line on rest of body.

4) Distinct tapering propodial tentacles, length about 25% of body width.

5) Scattered records around Britain and Ireland. Few or none in southern half of east coast England and north-east Irish Sea.

 

Carronella pellucida (Alder & Hancock, 1843). fig. 19 flic.kr/p/2nt1jUh & fig. 20 flic.kr/p/2nt1jQz

1) Cerata length greater than width of body.

2) White pigment covers entire distal end of cerata.

3) Opaque white dorsal line on tail. No line on rest of body.

4) Long tapering propodial tentacles as long as, or longer than, width of body.

5) Scandinavia and Scotland; the few English records on NBN are probably misidentifications.

 

 

Habits and ecology

C. gracilis lives sublittorally and at LWS on sheltered rocky shores with strong currents, on or near its hydroid prey; Eudendrium spp. fig. 09 flic.kr/p/2nt1krj , Halecium articulosum and Clytia johnstoni. Like other nudibranchs, it is a simultaneous hermaphrodite. Spawn is looped around its prey, or deposited as a spiral line on hard substrate fig. 21 flic.kr/p/2nt2wcr , in mid April, May and possibly other months. Veliger larvae emerge and drift as plankton before transforming into the adults.

 

Distribution and status

C. gracilis is recorded from Iceland to the Atlantic coast of France, and there are records in north-east America fig. 22 flic.kr/p/2ntJ4fN , GBIF map www.gbif.org/species/2292262 . Scattered records around Britain and Ireland and sometimes locally common. Few or none in southern half of east coast England and north-east Irish Sea. It is probably under recorded because of its small size and confusion with other Coryphella spp. UK distribution map, species.nbnatlas.org/species/NHMSYS0021185584 .

 

Acknowledgements

For use of images I gratefully thank Jim Anderson, Billy Arthur, Roy Dahl, Nathan Jeffery, Amy Newfield, Tim Nicholson, Poul Rasmussen and Alastair Skene, and I thank Simon Taylor for specimens. For helpful advice I thank Jeff Goddard and Angel Valdes.

 

References and links

Alder, J. & Hancock, A. 1845-1855. A monograph of the British nudibranchiate mollusca. London, Ray Society.

Family 3, plate 17. www.biodiversitylibrary.org/item/131598#page/350/mode/1up

Family 3, plate 18. www.biodiversitylibrary.org/item/131598#page/354/mode/1up

 

Korshunova, T., Martynov, A., Bakken, T., Evertsen, J., Fletcher, K., Mudianta, W.I., Saito, H., Lundin, K., Schrödl, M. and Picton B. 2017. Polyphyly of the traditional family Flabellinidae affects a major group of Nudibranchia: aeolidacean taxonomic reassessment with descriptions of several new families, genera, and species (Mollusca, Gastropoda). ZooKeys 717: 1–139. doi.org/10.3897/zookeys.717.21885

 

Thompson, T.E. & Brown, G.H. 1976. British opisthobranch molluscs. London, Academic Press.

 

Thompson, T.E. & Brown, G.H. 1984. Biology of opisthobranch molluscs 2. London, Ray Society.

 

Glossary

buccal mass = anterior of digestive system including an odontophore which supports the anterior of the radula, and a complex of muscles to operate them and other mouthparts.

 

cerata = (sing. ceras) lobes on dorsum of aeolids and some other seaslugs.

 

circum-oesophageal nerve ring = ganglia-bearing nerve cord which encircles the oesophagus.

cnidocytes = explosive stinging cells of Cnidaria. en.wikipedia.org/wiki/Cnidocyte

cnidosac = storage capsule at tips of cerata of Aeolidiidae for ingested unexploded cnidocytes.

 

digestive gland = large organ in gastropods which acts like the liver and pancreas in mammals to absorb food.

 

distal = away from centre of body or from point of attachment.

ganglia = (sing. ganglion) knots on a nerve cord containing sensory cell bodies that conduct impulses to (innervate) organs of the body.

 

LWS = low water spring tide; two periods of a few days each month when tide falls lowest.

 

notal = (adj.) of the back.

notal ridge = ridge on dorsal surface.

notum = (of seaslugs) the dorsal surface.

ovotestis = (pl. ovotestes) hermaphrodite organ serving as both ovary and testis.

propodial tentacles = tentacular, lateral extensions on anterior of the foot.

propodium = anterior portion of gastropod foot. (adj. propodial).

rhinophores = chemo-receptor tentacles on top of head of nudibranch.

veliger = shelled larva of marine gastropod or bivalve mollusc which moves by action of cilia on a velum (bilobed flap). Stage may be passed in plankton or within liquid-filled egg-capsule.

 

 

Done