Family RHYTIDIDAE Pilsbry, 1893

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Introduction

This large family of carnivorous land snails is found in Australia, New Zealand, islands of the western Pacific, Indonesia, the Seychelles and South Africa. In Australia, the family is confined to the eastern and southeastern regions except for one species that is found in the southwest of Western Australia.

The family is characterised by the small to large-sized shells with fine to coarse, simple, radial ribs. The shells are mainly yellow to dark honey to black with very little calcareous material, mainly conchin. The animal has no jaw, but has long curved radula teeth; a specialisation for carnivory.

Rhytidids 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 known to be cannibalistic, will readily preying 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.

Excluded Taxa

Misidentifications

RHYTIDIDAE: Helix namoiensis Cox, 1868 — Smith, B.J. 1992. Non-Marine Mollusca. In, Houston, W.W.K. (ed.). Zoological Catalogue of Australia. Non-marine Mollusca. Canberra : Australian Government Publishing Service Vol. 8 xii 408 pp. [303] (Helix namoiensis as a synonym of Strangesta (Namoitena) strangei (Pfeiffer, 1849)); Stanisic, J., Shea, M., Potter, D. & Griffiths, O. 2010. Australian Land Snails. A field guide to eastern Australian species. Mauritius : Bioculture Press Vol. 1 595 pp. [126] (considered to be a member of the American Haplotrematidae; type of the genus Namoitena)

RHYTIDIDAE: Namonitena Iredale, 1933 — Iredale, T. 1933. Systematic notes on Australian land shells. Records of the Australian Museum 19: 37-59 [49] (Namoitena introduced for Helix namoiensis Cox, 1868; Murphitella (Namoitena) namoiensis (Cox, 1868)); Stanisic, J., Shea, M., Potter, D. & Griffiths, O. 2010. Australian Land Snails. A field guide to eastern Australian species. Mauritius : Bioculture Press Vol. 1 595 pp. [126] (considered a synonym of an American taxon)

Diagnosis

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.

Diagnosis References

Stanisic, J., Shea, M., Potter, D. & Griffiths, O. 2010. Australian Land Snails. A field guide to eastern Australian species. Mauritius : Bioculture Press Vol. 1 595 pp. [126]

General References

Climo, F.M. 1977. A new higher classification of New Zealand Rhytididae ( Mollusca : Pulmonata). Journal of the Royal Society of New Zealand 7: 59-65

Laws, H.M. 1971. The chromosomes of some Australasian Paryphantidae. Malacologia 11: 217-224

Smith, B.J. 1970. Notes on the anatomy of Victaphanta atramentaria Shuttleworth and V. compacta Cox & Hedley, and the designation of a neotype for V. atramentaria. Journal of the Malacological Society of Australia 2: 13-21

Smith, B.J. 1979. Notes on two new species of rhytidid snails from Lizard Is. Nth 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(3): 86-90

Smith, B.J. 1992. Non-Marine Mollusca. In, Houston, W.W.K. (ed.). Zoological Catalogue of Australia. Non-marine Mollusca. Canberra : Australian Government Publishing Service Vol. 8 xii 408 pp. [299]

Smith, B.J. 1998. Family Rhytididae. pp. 1091-1093 in Beesley, P.L., Ross, G.J.B. & Wells, A. (eds). Mollusca: The Southern Synthesis. Fauna of Australia. Melbourne : CSIRO Publishing Vol. 5(Part B) pp. vi–viii, 565–1234.

Solem, A. 1959. Systematics of the land and freshwater Mollusca of the New Hebrides. Fieldiana Zoology 43: 1-234

Stanisic, J., Shea, M., Potter, D. & Griffiths, O. 2010. Australian Land Snails. A field guide to eastern Australian species. Mauritius : Bioculture Press Vol. 1 595 pp. [126-159]

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