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Families Anatomidae and Scissurellidae

Anatomidae and Scissurellidae are families of minute gastropods characterized by a slit or foramen for the exhalent water current. They are closely related to the large deep-water slit shells, the Pleurotomariidae, and to abalones, the Haliotidae, in which the slit has been modified to a number of separate holes. In contrast to those families, they are minute, all being less that 6 mm in size, and on average 0.8 - 1.5 mm. The family is of world-wide distribution, species occurring from the intertidal down to abyssal depths, including hydrothermal vents. There are about 170 described species, but probably many more undescribed.

The Scissurellidae has been used as a catch-all group for small vetigastropods with a slit. It had been divided into six subfamilies, two of which only occurr in hydrothermal vents. As a result of a phylogenetic analysis, Geiger (2004a) elevated the subfamily Anatominae to family status as Anatomidae, while pointing out that the remaining subfamilies are not closely related and require reclassification. There are about 16 genera, only five of which are represented in the NSW fauna.

There are seven species of the two families now known from NSW, an increase of three from Iredale & McMichael's 1962 Checklist. They have been poorly known because of their minute size, but some are quite common if the appropriate collecting methods are used. They are uncommonly found in beach shell grit, probably because of their fragility. Some are obtained from microscope sorting of dredge samples. Live specimens are obtained by washing intertidal rocks and algae.

Until the publications of Geiger and Jansen from 1999 onwards, the NSW species were not well documented. Several Australian species were described around the end of the 19th century and the start of the 20th, but interest was low until the publication of a summary of the Australian species by Jansen in 1999. In this work a number of undescribed species were identified. Subsequent to this, Geiger (2003) provided definitions of genera, followed by detailed treatment of the Australian species (Geiger & Jansen, 2004a, 2004b).

Family references

Geiger, D.L. 2003. Phylogenetic assessment of characters proposed for the generic classification of Recent Scissurellidae (Gastropoda: Vetigastropoda) with a description of one new genus and six new species from Easter Island and Australia. Molluscan Research 23:21-83

Geiger, D.L. & Jansen, P. 2004. Revision of the Australian species of Anatomidae (Mollusca: Gastropoda: Vetigastropoda). Zootaxa 415:1-35

Geiger, D.L. & Jansen, P. 2004. New species of Australian Scissurellidae (Mollusca: Gastropoda: Vetigastropoda) with remarks on Australian and Indo-Malayan species. Zootaxa 714:1-72

Coverage

All species known from NSW are treated here.

Scissurella ornata May, 1908 was described from Tasmania. It is listed as occurring in NSW in Iredale & McMichael's NSW checklist, and by Wilson (1993), probably following that list. I can find no specimens to confirm the NSW record; it may be a misidentification of Scissurella cyprina Cotton & Godfrey, 1938

Identification notes:

The shells of these families are minute, up to 3 mm in height, globular in shape, with umbilicus open, white in colour, with a slit in the margin or foramen behind the margin (Fig. 1). The selenizone is the scar left by the slit as the shell grows. In the Anatomidae, the slit is at the periphery of the last whorl, but in the Scissurellidae, the slit or foramen is on the shoulder, above the periphery of the whorl. Anatomidae is represented in NSW by only two species of Anatoma, which have a marginal slit. The Scissurellidae is represented by five species, with slit or foramen; in Incisura and Scissurella there is a slit at the margin, while in Sukashitrochus and Sinezona the slit is closed to become a foramen.