Alder & Hancock, 1845
Description:
The length of this species reaches 38 mm. The colour pattern, while it may appear conspicuous in the laboratory, renders the animal cryptic in the field, with the red-brown body covered dorsally with white specks. The dorsum and the flanks bear small ridges and tubercles. The pallial rim and a mid-dorsal pallial ridge are notable, the latter being continued posteriorly into a dorsal metapodial keel. Rare specimens may be pinkish white, shaded with yellow. The lamellate rhinophores and the gills are brown; the latter are tripinnate, up to nine in number, around the anal papilla. Each rhinophore may have up to seventeen lamellae. The sides of the head are produced to form flattened oral tentacles.
Habitat:
G. castanea lives in shallow water offshore, down to 25 m. Rarely it may be found in the inter-tidal zone. The prey is always an ascidian, especially Ascidia mentula, Botryllus schlosseri or Botrylloides leachi.
Distribution:
This species has a world-wide distribution, from Norway to the Mediterranean Sea, Red Sea, New Zealand and Japan (Distr. G. castanea).