Smaragdinella calyculata
(Broderip & Sowerby, 1829)

Order: CEPHALASPIDEA
Superfamily: HAMINOEOIDEA
Family: Smaragdinellidae

DISTRIBUTION

Widespread Indo-West Pacific.

PHOTO

Upper & Lower Right: Druelu, Lifou, Loyalty Ids, New Caledonia, November, 2000. Many animals 14-20 mm long. AM C390347. Photos: Bill Rudman
Lower Left: Shells of animals from Manana Islet, Oahu Is, Hawaii, 1924. AM C61285 [largest shell 12mm long] Photo: Bill Rudman

Smaragdinella calyculata is green, sometimes with brown or white blotches along the edge of the parapodia. It is herbivorous. Smaragdinella is the closest thing to a 'limpet' amongst the cephalaspid 'bubble shells'. It lives at the same place on the shore as many limpets, and its compact shape and large muscular foot make it difficult to prise the animal off the rock at low tide. Its habit also resembles that of the sea hare Dolabrifera. Its anatomy however clearly shows that it is closely related to herbivorous bubble shells such as Haminoea and Phanerophthalmus. Its shell is very flattened, reduced to little more than the body whorl. Miller (1969) noted that in the Solomon Islands this species attached firmly to open, exposed rock surfaces, and produced large amounts of mucus, sometimes becoming very difficult to prise off. It was found uncovered at low water and was kept moist by the ocean spray. I haved observed similar behaviour in Lifou, Loyalty Ids.

The large headshield is relatively wide in front, narrowing slightly to form a rounded bilobed posterior end. The chemosensory Hancock's organs are brown and form a thin wrinkled ridge in the groove between the foot and the headshield on each side of the head. The penial opening is on the right anterior corner of the head and from it a ciliated seminal groove runs back to the genital opening at the anterior end of the mantle cavity opening. On each side the foot extends into a large lateral lobe, the parapodia, which fold over, partially enclosing the shell, which lies exposed on the the back of the animal. The shell is brownish green. It is relatively solid and flattened, reduced to little more than the body whorl. The upper whorls absent, except for a spoon-shaped projection from the columella. There can be some variation in shell shape, the extremes of shape illustrated in the photos in an accompanying message. However all variants can be found at the same locality so they are unlikely to represent specific differences.

The phylogenetic relationships of Smaragdinella are clearly seen when the alimentary canal is looked at. The broad radular ribbon, has many rows of hook-shaped teeth, reminiscent of HaminoeaAtys, and there is a gizzard with 3 chitinous plates bearing sculptured on the inner side with countless minute V-shaped grooves.

Many species of Smaragdinella have been described from their shells alone. Rudman (1972) showed that the shell of S. calyculata is very variable and it is possible to synonymise the species down to two or three species. One of these is the closely related species, S. sieboldi A. Adams, 1864, which is found in Japan, commonly on seaweeds and among oysters and barnacles between tide marks (Habe, 1964).

References:
• Habe, T. (1964) Shells of the Western Pacific in Colour. Vol.II. Hoikusha, Osaka. 233 pages.
• Miller, M. C. 1969. The habits and habitats of the opisthobranch molluscs of the British Solomon Islands, pp. 541-548. [In]: E. J. H.
Corner. A discussion of the results of the Royal Society Expedition to the British Solomon Islands Protectorate, 1965. Philosophical Transactions of the Royal Society London, series B, Biological Science, 255(800): 285-631.
• Rudman, W.B. (1972) The herbivorous opisthobranch genera Phanerophthalmus A. Adams and Smaragdinella A. Adams. Proceedings of the malacological Society of London, 40(3): 189-210, 11 figs.

Authorship details
Rudman, W.B., 2004 (January 12) Smaragdinella calyculata (Broderip & Sowerby, 1829). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/smarcaly

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