Behaviour and Locomotion
Crypsis
Acanthochitona sp., like many other Acanthochitona species, is cryptic, as they are found on the underside of coral rubble, concealed in small holes and crevices (Gowlette-Holmes 2001). Their size, elongate body and attaching mechanism of the foot and girdle allow them to exploit this habitat. Animals that live on the intertidal zone are very susceptible to dessication from the sun and wind, and the coral rubble provides an area for Acanthochitona sp. and many other invertebrates to reside during the low tide, providing protection from waves, predators and desiccation. Most mobile molluscs are herbivores, and a common pattern is that marine mollusc herbivores become active at high tide (Little 1989). Most polyplacophorans become active and feed at high tide especially at night, when rocks are submerged. They are usually motionless at low tide, residing under rocks due to being negatively phototactic, meaning they move away from light sources (Ruppert et al 2004). As Acanthochitona species are found under/in rock and were not observed on the upper side of boulder at Heron Island, they are most likely negatively phototactic, residing in the coral rubble during low tide to protect from desiccation and become active during high tide, perhaps at night, to feed. Acanthochitona sp. dorsal colourings resemble the colours found on the upper side of the coral boulders and this may provide clues to their behaviour, suggesting they may feed on the upper side of the boulder, while successfully camouflaging.
Homing
Some polyplacophoran species, such as Acanthopleura gemmata, have a homing ability and are able to return to a a specific area known as their "home scar" after foraging (Ruppert et al 2004, Hulings 1991). No observations were made on Heron Island to suggest that Acanthochitona sp. demonstrate such an ability and there also appears to be no studies that investigate potential homing patterns of Acanthochitona species. Therefore it in unknown whether Acanthochitona sp. has the ability to home or not.
Locomotion
Acanthochitona sp., like all polyplacophorans, use their muscular foot on the ventral surface to attach to substrate. Locomotion is facilitated by the ciliated sole of the foot and excretion of mucous, to move along a substrate (Ruppert et al 2004). By contracting and relaxing the longitudinal muscle fibres in the basal area of the foot in a wave-like motion (from anterior to posterior), polyplacophorans are able to "creep" forward slowly. They can also rotate the direction of the foot and move backwards using the same motion (Kaas et al 1998). Most polyplacophorans are slow moving and Acanthochitona sp. appeared to be slow moving, from undocumented observations on Heron Island. Due to the articulating valves and flexible body, polyplacophorans are able to move over any shaped substrata with ease and are also able to curl up (see Defences). The girdle has lateral and longitudinal fibres that are used to clamp down the girdle onto the substrate (Kaas et al 1998). The foot also does this, adhering the chiton to that particular area, making them very hard to remove. Polyplacophorans do this if they feel threatened or to resist desiccation. Acanthochitona sp. demonstrated this behaviour when trying to remove the animal from a piece of coral boulder. They can also raise their girdle to release excretory products or gametes through the exhalent aperture (Kaas et al 1998).
Defence
From observations made at Heron Island, Acanthochitona sp. has the ability to curl up into a ball when disturbed, lying on its dorsal side and covering up the ventral soft parts of the body. All polyplacophorans have this ability, and it is achieved by the chiton contracting the lateral longitudinal muscle, found around the whole animal, just below the margins of the shell valves (Kaas et al 1998). This causes the anterior and posterior parts of the body to curve inwards. This defence mechanism is used when the chiton becomes detached from the substrate or is disturbed and it is also used by the animal to manoeuvre itself to allow the foot to be reattached to the substrate (Ruppert et al 2004, Kaas et al 1998).
Figure 1: Acanthochitona sp. defensive mechanism, curling up in a ball to cover the ventral soft body parts. |