Growth and Development
Internal fertilisation occurs in L. vitellus after a male inserts his penis into a female body during copulation (Burgess, 1985). After copulation, the female deposits her fertilised eggs in capsules that are moulded and attached to the substrate by the foot (Burgess, 1985). During the brooding period, the female covers the egg mass with her foot for up to 4 weeks (Burgess, 1985). Division of the ovum begins 24 hours after the eggs have been deposited (Burgess, 1985). Once capsules erupt, pelagic veliger larvae are released into the water column (Burgess, 1985). Time in the pelagic stage varies, however once they reach the bottom a new shell whorl is secreted (Burgess, 1985). This begins the oliviform or "bulla" stage (Burgess, 1985).
Cowries that have metamorphosed as an oliviform "bulla" continue to grow in a spiral, with each whorl being deposited by the mantle (Burgress, 1985). The bulla stage in shells can not only be distinguished from adult cowries by their oliviform shape, but also due to their uniform shell colouration (Burgess, 1985). Colour patterns are laid down when maturity is reached (Burgess, 1985). This occurs when the outer lip of the shell is turned inwards, thickened, and teeth are formed on both lips, becoming the characterisitc slit-like aperutre of the Cypraeids (Burgess, 1985). Growth is determinate in cowries as shell and soft body size does not increase after the juvenile stage (Wilson, 1985). Cowries are permanently attached to their shell due to the columellar muscle that fixes the animal to the shell (Ruppert et. al, 2004). This muscle is also responsible for withdrawing the head and foot into the shell (Ruppert et.al, 2004). It originates on the columella, the central anatomical feature of the coiled shell, and inserts on the operculum in the foot (Ruppert et.al, 2004).
During larval formation, L. vitellus undergoes torsion which is a defining characteristic of the gastropods (Ruppert et. al, 2004). Torsion is a 180o counterclockwise rotation of the visceral mass, shell, mantle, and mantle cavity (Ruppert et. al, 2004). The head and foot remain unaltered by this rotation (Ruppert et. al, 2004). Torsion places the mantle anterior to the head to allow the head to be retracted into the safety of the shell when danger is present (Ruppert et. al, 2004).
Cypraeids exhibit female-biased sexual dimorphism (SSD), with females maturing at a larger size than males (Irie et. al, 2008). Because this species is a determinate grower, development is mediated by a longer development time in females (Irie et. al, 2008). L. vitellus is considered polyandrous as there is no evidence that a female mates with only one male (Wilson, 1985). Juvenile individuals and brooding females are found throughout the year, therefore generations overlap considerably (Wilson, 1985).
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