Cavoliniidae Family
Family Cavoliniidae
Cavoliniids are pteropods, spending their complete lifecycle as plankton in the water column and are the most numerous and diverse of such holoplanktonic molluscs. They occur in all the oceans showing greatest diversity in the tropical seas but greatest abundance in colder climes. Most inhabit the surface waters of the sea down to approximately 200 metres.
The most prominent features of cavoliniids are their large wings that protrude from the aperture of their bilaterally symmetrical shell. These muscular wings are formed from the anterior portion of the foot. The thin shell, into which the animal can withdraw for protection, has lost the spiral coiling of the more primitive pteropods and shows great variety of shape. The shells can be needle shaped, either straight or pointed, triangular or pyramidal that may taper posteriorly whilst others are bottle shaped or globular. Dorsal or lateral spines are present in some. There is no operculum and the external mantle can envelope the whole of the shell. The head is small and ill defined with the depressed mouth dorsally located between the wings and surrounded by three ciliated lobes formed from the remainder of the foot. A pair of tentacles is situated dorsally in the neck region, the right tentacle being larger than the left. Their planktonic prey is trapped by use of a spherical web of mucus, many times the size of their bodies, which is drawn towards the mouth by the action of cilia on the wing surfaces and surrounding lobes. A small radula pulls the food into the gut.
Cavoliniids are generalist feeders consuming foraminiferans, diatoms and dinoflagellates amongst others. Only some, the Cavolinia and Diacavolinia, possess gills. These are secondary structures in the mantle cavity. Although cavoliniids drift along in the planktonic currents they are able to swim for ascending in the water column and for escape purposes by the flapping of their two wings. They are capable of buoyancy regulation and a number of features contribute to retard sinking including the large feeding web, the light shell, the mantle extrusions, and posture to increase surface area. The Cavolinia and Diacavolinia employ a temporary (jettisoned if disturbed), gelatinous pseudoconch that combined with the extended mantle assists in arresting sinking when not actively swimming. Essentially hermaphrodites, cavoliniids exhibit protandric sexual development whereby they are initially males that develop into hermaphrodites and then later become female. The majority release free-floating egg masses that hatch into veliger larvae.
