Large populations of both the adult and juveniles P. sulcatus, are commonly found to occur on stones, rocks and boulder rubbles in intertidal environments throughout their global distribution range (Houbrick 1987; Rohde 1981). P. sulcatus predominantly occur lower in the vertical distribution along the shore; in the upper and middle zones of intertidal environments (Houbrick 1987; Rohde 1981). It is the least cryptic amongst other planaxid species and is often seen exposed on rocks, stones and boulders in aggregates during low tides (Houbrick 1987). At low tide, the animal withdraws into its shell behind the operculum and attaches itself via the lip of the shell to the substratum with mucus (Ruppert, Fox & Barnes 2004). Being active crawlers, P. sulcatus taking refuge beneath rocks, boulders and rubbles or in crevices, emerges at the incoming tide to graze on microalgae encrusting the substrates (Houbrick 1987; Rohde 1981). On Heron Island, P. sulcatus are believed to be grazing on algal species including Entophysalis deusta, Callothrix crustacea, Schizothrix arenaria and Kyrtuthrix maculans (Rohde 1981).
P. sulcatus populations on Heron Island were observed to be highly stable over time (Rohde 1981). Populations of P. sulcatus in different parts of the habitat on Heron Island are independent and well separated from each other, with little mixing of individuals over short distances (Rohde 1981).
P. sulcatus are hosts to a large diversity of trematode species (Phylum: Platyhelminthes, Class: Trematoda) (Ching 1989; Houbrick 1987; Rohde 1981). Populations of P. sulcatus on Heron Island were observed to be infected with at least one species of Aspidogastrea and 6 species of cercariae trematodes (Rohde 1981). Despite being heavily infected by trematode parasites, the population size and biomass of P. sulcatus and their parasites on Heron Island had remained remarkably constant through time (Rohde 1981).
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