Planaxis sulcatus, commonly known as the Furrowed Clustewink, is a marine intertidal prosobranch gastropod species. They are members of a small, monophyletic family; Planaxidae, that is placed within a larger superfamily Cerithiacea. P. sulcatus was thought to have evolved during the Pliocene and the first fossil records of the species was discovered in Sonde (Madioen), Java, Indonesia (Houbrick 1987) .

                                                    Illustration of Planaxis sulcatus, Born 1778.
                                                   Illustrated by: Lai H.R

It is medium-sized for a marine gastropod and adults can measure up to 35 mm in length (Houbrick 1987). Sexual dimorphism is exhibited in P. sulcatus as female individuals are generally larger in size than the males (Ohgaki 1997). The shell of P. sulcatus is conic-ovate in shape and appears greenish brown-black with white spotted patterns (Houbrick 1987). It is easily distinguishable based on the dark purple colouration of the inner lip, lining the ovate aperture (Houbrick 1987). The head-foot is yellowish-green in colour with black horizontal stripes (Houbrick 1987). The anterior region bears a pair of long, black cephalic tentacles on either side of the large downward pointing, black coloured snout, that is flared into a crescent-shaped oral hood at its tip (Houbrick 1987). The foot is short and the sole is white to dirty white in colour (Houbrick 1987).

                                                                       Furrowed Clustewink (Planaxis sulcatus)

P. sulcatus have a broad geographical distribution range and are commonly found to occur along coastal rocky shorelines throughout tropical Indo-Pacific region including in Australia, Southeast Asia, Africa, the Red Sea and in the Persian Gulf. They are found to occur in abundances along the shore, in the upper and middle zones of intertidal environments (Houbrick 1987). P. sulcatus is the least cryptic species among the planaxids and is often seen exposed on rocks, stones and boulders in aggregates during low tides (Houbrick 1987; Rohde 1981). They can also be found taking shelter in crevices and under large boulders and rocks for protect themselves from desiccation exposed in the tropical heat of the sun (Houbrick 1987; Rohde 1981).

P. sulcatus are herbivorous (Houbrick 1987; Rohde 1981). At low tides, P. sulcatus withdraws into its shell behind the operculum and attaches to the substratum with mucus via the lip of the shell (Ruppert, Fox & Barnes 2004). During the high tides, it will emerge from its resting position when the tide is low and crawling at the incoming tide to actively graze on microalgae encrusting the substrates in its habitat (Houbrick 1987; Rohde 1981). When crawling, P. sulcatus frequently touch the substrate with their long tapering cephalic tentacles one at a time, waving back and forth in a rhythmic manner (Houbrick 1987). The ventral-lateral position of the eyes on the tentacle bases, places them close to the substrate thus, enabling the animal to see the substrate at all times while moving (Houbrick 1987). The large extended oral hood at the snout tip is also in constant contact with the substrate while crawling, moving left and right in a vacuum cleaner fashion to allow for constant grazing on microalgae (Houbrick 1987).

Contary to suggestions that P. sulcatus are parthenogenetic, it is actually a Gonochoristic, ovoviviparous species that rears its embryos in large brood pouches (Houbrick 1987;Ohgaki 1997). P. sulcatus is an example of a species of prosobranch gastropod that is capable of utilising several reproductive modes, in response to environment or geographical difference (Houbrick 1987). Embryos may hatch at the veliger stage to become planktontrophic larvae, at a late veliger state as lecithotrophic larvae or be brooded throughout the embryonic development stage to hatch as juvenile snails (Houbrick 1987; Rohde 1981). Mating is observed in P. sulcatus to occur during summer, where copulation between a male-female pairs is frequently observed (Rohde 1981).

P. sulcatus often play hosts to a large diversity of trematode species (Rohde 1981). However, despite being heavily infected by trematode parasites, the fitness of the snails does not seem to be affected at all (Rohde 1981). At present, threats threatening the survivability of the species Planaxis sulcatus have not been evaluated by the International Union for Conservation of Nature (IUCN). However, pollution of the marine environment due to anthropogenic activities could potentially pose a serious threat to the survivability of P. sulcatus in the future (Sarkar et al. 2006).