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Spongiobranchaea australis d'Orbigny, 1836

Overview

This is a large, naked pelagic snail, over 2 cm long, with a semi-transparent body. The chromatophores give the body a brown to violet colour, only the ring-shaped lateral gill and wings are white. There are two strong lateral arms, a median arm is absent. The arms have 10 suckers each. A posterior gill and lateral gill are present. The posterior footlobe is typical in size as are wings and lateral footlobes. It is a carnivorous species that lives at shallow and great depths in the Southern Ocean (Spongiobranchaea australis).

Taxonomic Description

Body long, oval shaped, with a dark brown or violet colour due to numerous chromatophores, which are only absent on gills, footparts and wings. The wings are oval shaped, narrow at the base and pointed at the distal end. Lateral and posterior gills are present. The lateral gill more or less surrounds the body in its middle region. The posterior gill is also circular shaped but both gills are simple. Anterior tentacles are long. Lateral footlobes attached over their entire length. Median footlobe rather long and pointed. The median foot tubercle is present, as is the dorsal gland patch. The radula shows a red colour from the reddish basal membrane and the red median teeth. The Spongiobranchaea australis radula formula is 8-1-8 in the last and 5-1-5 in the younger rows. The number of rows may be 35. The median plate is formed later than the lateral ones and it is lacking in the first transverse rows. The median plate is strong, with one central cusp and one or two smaller cusps at each side, near the margin. The first Spongiobranchaea australis lateral teeth show an additional cusp (Spongiobranchaea australis radula). The Spongiobranchaea australis sucker arms bear 7 to 10 suckers on short peduncles, the three or four proximal ones are relatively small. The hook sacs are small in comparison to those of Pneumoderma. In the Spongiobranchaea australis buccal mass, the hooks, about 20 in number, are rather long. The jaw is composed of cusps placed in two groups on a median projection of the ventral buccal wall. The two groups of cusps caused Massy (1920) to consider that two jaws were present.
The maximum body length is 22 mm.

Juveniles

A special description is not available.

Reproduction

This species is a protandric hermaphrodite.

Ecology

This species is a carnivore.

Distribution

It is restricted to the S-Atlantic Ocean and Antarctic waters, see the Spongiobranchaea australis map. Though exact localities for most of the southern Pacific Ocean are unknown the distribution is certainly circumpolar. Influences of surface currents on its range are evident. Penetration into the Peru and Agulhas current and Madagascar area can only be explained by a northward transport by currents.

Types

Spongiobranchaea australis d'Orbigny, 1836: 131, pl. 9, figs. 1-7.
Types not found in MHNP, and not in BMNH where the type should be present.
Cliodita caduceus Quoy and Gaimard, 1824: 413, pl. 66, fig. 1.
Type is lost according Pruvot-Fol (1932: 507).

Spongiobranchaea australis