Archerd Shell Collection
> Shell Classes > Polyplacophora > Chiton Anatomy |
Like the mantle of gastropods, a girdle of muscular tissue
surrounds the chiton body, and the shell plates are partially embedded, on the dorsal
(top) side. The chiton moves on its foot, like other molluscs. The muscular girdle gives
structural support for the shell plates and a complex muscle system articulating the shell
plates. Chitons, for example can roll into a ball for protection. In several species the
girdle also can be used like a net, to capture small food particles. . A comparatively simple body plan is found, with a straight-line arrangement of the visceral organs, somewhat like that of the Monoplacophoran gastropod, Neopilina galatheae, mentioned earlier (see Shell Classes). Multiple gills are suspended over the pallial (mantle) cavity from its roof. The other visceral organs are less well defined. For example, the tubular ventricle of the heart is surrounded |
| by the auricle and separated only by a stiff
membrane with one or two paired ports between them. In turn, the muscular portion of the
heart surrounds the auricle. The heart is weakly contractile, and pumping the hemolymph is
aided by generalized muscle movement of the body. No well defined arteries or veins are
found. Oxygenated hemolymph is distributed through sinuses and interstitial spaces.
Hemocyanin, the oxygen transport molecule, is dissolved directly in the lymph. A long nephridial sinus runs the length of the chiton terminating in a nephridial pore for urine excretion. The |
nephridial pore is located at the posterior end.
Osmotic regulation seems not to be present, as chiton body fluid is iso-osmotic with sea
water. The chiton nervous system is more like an oval-shaped nerve net. Ganglia are sparse, poorly defined, and largely found in the buccal area. Most chitons have separate sexes, but they are not dimorphic. A few are hermaphroditic and capable of self-fertilization; however, their sperm clusters mature later than do the female gonadal tissues (Beesley et al. 1998). |
Archerd Shell Collection
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