Summary
Taxonomy
Physical Description
Ecology
Life History & Behaviour
Anatomy & Physiology
Torsion and the mantle cavity
Nervous system
Sensory systems
Reproduction
Internal transport
Feeding mechanisms
Digestive system
Respiration
Excretion
Foot anatomy
Evolution & Systematics
Conservation & Threats
References & Links |
Torsion and the mantle cavity
Figure 4. Labelled, generalised plan of
gastropod exhibiting torsion, where the
mantle cavity and associated organs
are placed anteriorly above the head.
Redrawn from Fretter & Graham, 1994.
C. parthenopeum, similarly to other gastropods, undergoes torsion, where the gut and nervous system are twisted into an anterior position above the head along with the mantle cavity. This results in the position of the anus and osphradium being above the head. Although this proves to be an interesting arrangement, where feces would be release from above its head, it does have certain advantages. Water entering the mantle cavity would not be contaminated by sediment stirred up by the movement of the organism. This way, water flowing through the ctenidium would not be heavy with particulates, preventing it from being clogged. Also, forward movement of the animal causes a rise in positive pressure in the mantle cavity, helping water flow over the lateral cilia of the ctenidial filaments (Purchon, 1977). The osphradium would also be able to more accurately detect chemical cues in the water and judge its quality of water flowing into the mantle cavity (Laxton, 1971; Purchon, 1977). The osphradium are also used to supplement the cephalic sense organs. A great benefit for gastropods to undergo torsion is the space that the mantle cavity provides. The floor of the mantle cavity is formed by the dorsal surface of the head-foot, which forms the mantle skirt. This is also where new shell material are secreted. This enables the organism to retract its head, foot and tail into the mantle cavity when in danger, finally covering the apertural opening with its operculum, which is located at the dorsal surface of the tail. In these animals, there is only one gill, osphradium and kidney, due to the other set of organs being compressed and lost (Purchon, 1977). |
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