Gascoignella aprica
Jensen, 1985
Order: SACOGLOSSA
Superfamily: ELYSIOIDEA
Family: Gascoignellidae
DISTRIBUTION
Known only from Hong Kong
PHOTO
Tsim Bei Tsui, Hong Kong in April 1998. I think its size is about 8-10mm Photo: Kathe Jensen
This unique sacoglossan is known only from the Jensen's original description which is summarised below:
The Family Gascoignellidae is characterised by having no rhinophores, cerata or parapodia. The visceral mass is distinctly set off from head-foot region. Foot only slightly longer than head.
The genus Gascoignella is characterised as having a ventro-lateral anus on the right side, in a groove between the visceral mass and foot, usually hidden by foot. The penial opening also on right side in a small notch on the head near the lateral margin, approximately at he level of the right eye. The oviducal opening is close to anus. The subintestinal ganglion is very small, almost fused with the abdominal ganglion.
Gascoignella aprica is almost entirely black on the dorsal surface. The eyes are surrounded by light, yellowish transparent areas. The head is a lighter black than the visceral mass. The foot sole is yellowish-white, and the ventral surface of the visceral mass is dark green from the contents of the digestive gland. It superficially resembles a small turbellarian and is up to 8mm long when crawling. It is very flat with no traces of rhinophores, cerata or parapodia. The head-foot region is very distinctly set off from the visceral mass. The anus and genital openings cannot be seen in live animals but Jensen reports that in a specimen relaxed in MgCl2 the anus was seen lateroventrally in the groove between the foot and the visceral mass on the right side. There is no external demarcation of the pericardium, but the heart-beat is visible through the dorsal epithelium of the anterior visceral mass. The mouth is located in the distinct groove formed between the anterior border of the foot and that of the head. This groove forms distinct notches laterally on the head. There is no median notch in the anterior margin of the foot.
It was found living intertidally on mats of filamentous green algae, predominantly Chaetomorpha sp. The animals were most often crawling about in the open sunlight but were occasionally found inside the algal mat. Jensen reports that they are very resistant to desiccation as long as they are supplied with moist algae, but died in a few hours when placed on a dry glass surface. They were also very resistant to starvation. A few specimens survived in a small container for about 3 months after the disappearance of all visible algal material. They shrank considerably in size but otherwise appeared healthy and active.
Only a few sacoglossans totally lack cerata as well as parapodia and rhinophores [Limapontia capitata, L. depressa, Platyhedyle denudata]. Bosellia spp have short rhinophores, but lack cerata and parapodia, and Alderia modesta has numerous cerata but no rhinophores.
Reference:
• Jensen, K. (1985). Annotated checklist of Hong Kong Ascoglossa (Mollusca: Opisthobranchia), with descriptions of four new species. [In] Proceedings of the Second International Workshop on the Malacofauna of Hong Kong and Southern China. Morton, B. & Dudgeon, D. (eds). Hong Kong University Press, Hong Kong. 77-106
Rudman, W.B., 2003 (July 14) Gascoignella aprica Jensen, 1985. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/gascapri
