Feeding
Acanthochitina sp., like all polyplacophorans, uses its radula (Figure 1), consisting of tiny chitinous teeth to scrap food off hard substrates. Most polyplacophorans are generalist grazers, feeding on algae and other small organism such as animals, but there also is a lot of variation in feeding preference of polyplacophorans, some being specialist (limited diet of a specific food source), carnivores and macroherbivore feeders (feeding on large algae) (Ruppert et al 2004, Kaas et al 1998). This scraping technique also removes sediments from rocks, meaning sediments constitute a large amount of polyplacophoran diets (Ruppert et al. 2004).
Acanochitona sp. radula has prominent tridentate magnetite capped teeth to scrape food off hard substrates. The reinforcement of teeth with an iron-mineral such as magnetite is said to be an adaptation to strengthen the teeth to allow continual removal of algae from rocks (Ruppet et al 2004, Shaw et al 2009). This demonstrates that algae is a likely food source of Acanthochitona sp, although little is known about the particular feeding habits of the sub-family Acanthochitoninae, in which this species occurs (Kaas et al 1998). Acanthochitona crinita, that also has tridentate cusps and is a herbivorous grazer that feeds on many different algae such as the corallie algae, Corallina elongata (Kaas etal 1998, Bode 1989). Acanthochitona sp. was found on parts of coral boulders that were dominated with different algae, especially encrusting coralline algae, suggesting that Acanthochitona sp. is an algal grazer too, like its relative. Another Acanthochitona species, Acanthochitona retrojecta that is also found in Australia, is very abundant on coralline algal turfs, where they complete their life cycle, which is likely due to their preference to feed on coralline algae (Kelaher and Cole 2005).
In all polyplacophoans, such as Acanthochitona sp., the radula occurs just inside the mouth in the buccal cavity, in the radula sac and on top of the odontophore, which provides support to the radula. Underneath the radula is the subradula sac which contains a chemosensory organ known as the sub radula organ, which is protruded onto the substrate to detect food (Ruppert et al 2004, Kaas et al 1998). Retractor and protractor muscles attach to the radula and the odontophore which move the radula anteriorly and posterior, allowing it be protracted and retracted from the mouth (Ruppert et al 2004). The radula is moved backwards and forwards and scrapings of algae are pulled back into the buccal cavity on each backward stroke (Ruppert et al 2004)(Figure 2).
Figure 2: Mechanism for feeding of polyplacophoran using a radula. 1. Radula moves from this position ventrally through the mouth and the radula move forward over the substrate. 2. Backwards stroke of radula, moving scrapings into buccal cavity. A= Odontophore. B= Radular sac. C=Radula teeth. D= Salivary gland. E= Subradular organ. F= Subradula sac. G= Buccal cavity. H= Mouth. Adapted from Ruppert et al 2004.
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