Rhytidid searching for the slime trail of the larger Giant Panda Snail

Rhytidids are a family of carnivorous snails that in eastern Australia range in size from minute to large (approx. 2-45mm range in shell diameter). Shell shape in eastern Australian species ranges from subglobose to discoidal and the shells are generally thin, translucent and lightweight. Teleoconch sculpture in the adult shell may consist of either radial ribs (usually limited to the upper half of the whorls) or spiral striae and wrinkles, or a combination of both. Protoconch sculpture is variable. The shell surface is covered in a prominent smooth periostracum which is generally glossy and sometimes gives the appearance of being lacquered. In some species the periostracum is very thick with little or no calcified element to the shell. The spire varies from flat to low dome-shaped and whorls are rounded with moderately impressed sutures. Most species are umbilicate and often with radial sculpture inside the umbilical cavity. The lip is thin, not reflected and undifferentiated from the columella. There is generally no columellar twist or ornamentation. Shell colour ranges from greenish-yellow to dark reddish-brown. Some southern Australian and New Zealand species are black. Colour patterning consists of darker radial streaks and bands while some species have a yellow spiral band around the umbilicus.

Rhytidid animals generally have elongated necks and relatively small heads which bear pointed protuberances below the tentacles and on each side of the mouth – a feature in common with some other carnivorous families such as the Central American Oleacinidae. The buccal mass is prominent when everted, there is no jaw (agnathous) and the radula bears pointed curved, lanceolate teeth. Rhytidids are oviparous and lay relatively large oval eggs. Their diet generally consists of snails and other invertebrates such as earthworms. They are also known to be cannibalistic and will readily prey on each other. Animal colour varies from orange-brown to bluish-grey and a coloured dorsal stripe is usually present down the length of the head and neck.

All of the eastern Australian rhytidids are ground dwellers and shelter under logs, rocks and deep, moist leaf litter on the forest floor.

The family ranges from South Africa to the Seychelles across to New Zealand, Papua New Guinea and some western Pacific Islands such as New Caledonia. In Australia they are found in eastern, southern and southwestern Australia.

References

Smith, B.J. 1979. Notes on two new species of rhytidid snails from Lizard Island. North Queensland. Records of the Australian Museum 32: 421-434.

Smith, B.J. 1987. Description of a new genus of carnivorous snail (Mollusca: Rhytididae). Victorian Naturalist 104: 86-90.