Mitchell's Rainforest Snail

Thersites novaehollandiae has a depressed-globose to more elevated shell with a closed umbilicus. The body whorl is rounded in most specimens. Shell height ranges from 19.9 to 64.2 mm and shell width from 31.1 to 71.6 mm, with a shell height-to-width ratio of 0.61–1.18. The reproductive anatomy is variable. The flagellum is 7.4–11.5 mm long and usually has a sharp tip, while the distal portion of the epiphallus measured in the 2025 revision ranges from 3.8 to 28.1 mm. Spiral lines on the surface of the body whorl may be present or absent.

Thersites novaehollandiae occurs in eastern New South Wales, Australia. Under its revised taxonomic circumscription, its distribution includes localities previously attributed to both T. novaehollandiae and T. mitchellae. Historically, T. novaehollandiae sensu stricto was reported from temperate and subtropical rainforest in eastern New South Wales, while populations identified as T. mitchellae were principally recorded from the coastal lowlands of north-eastern New South Wales.