Gastropod reproduction occurs via a multitude of mechanisms,thus anatomy is highly variable within the class. Literature on gastropod development is usually restricted to larval development, while early development seems to be limited (Calvo & Templado, 2004).
Trochidae are prosobranchs meaning they usually have separate sexes (gonochoric), where the gonad (ovaries or testies) are located in visceral mass. External fertilisation takes the place of copulation as the gametes are swept from the mantle cavity by the respiratory currents produced (Ruppert,Fox & Barnes, 2004). Once fertilisation has occurred in the plankton, development takes place to form a larva.
Larvae of aquatic invertebrates are usually planktonic, but may less commonly be benthic. Overall duration of the larval period varies highly, lasting from just a few hours to more than a year. Planktonic larvae can be separated into three different trophic groupings (planktotrophy, facultative planktotrophy and lecithotrophy) purely based on ability to concentrate and capture food particulate (Jaeckle & Manahan, 1989).
Underwood (1974) stated that the larvae of Austrocochlea Constricta is a lecithotrophic non-feeding larvae, meaning it is entirely dependent on internal energy sources (yolk). These short-lived larvae depend on the maternal supply of a yolk from the egg into the embryonic endoderm in order to survive. Due to the short-lived nature of lecithotrophiclarvae, limited dispersal capabilities are available to A. Constricta, compared to longer lived larvae. However even during this short time frame they may be transported substantial distances (Ruppert, Fox & Barnes, 2004).
Settlement:
Gastropods are generally specialised for certain habitats,meaning settlement phase is crucial. Nevertheless processes of development within the larva may force settlement, independent of suitable habitat or not (Ruppert,Fox & Barnes, 2004). When a suitable habitat has been identified settlement may take place either side of meta-morphosis (Ruppert, Fox & Barnes, 2004). Some important signals which aid in suitable habitat selection are surface texture, light intensity and substratum present. |