Reproduction and Development

Development
Veliger larvae of closely related strombids have been described in detail by Berg (1972). The veliger larvae of Strombus maculatus collected from the plankton were shown to resemble adult snails, except for the presence of a six-lobed velum and the lack of a proboscis. The eyes were well developed, with a ring of pigmentation present around the black pupil. The body was flesh coloured and translucent, but the sole of the propodium was black. In larval form, when the animal withdraw the operculum on the dorsal surface of the metapodium completely covers the aperture. Metamorphosis was shown to generally take place during the night and without any special substrate requirements. The shell surface became sticky after metamorphosis and was subsequently covered with algae and detritus. Green blotches appeared over the entire body and small white blotches were spaced at even intervals within the translucent cephalic tentacles. The body was covered with green and white blotches, with the distal three quarters of the proboscis remaining white one week after metamorphosis. Each week, the snail shell length grows approximately one millimetre and green and white blotches continue to appear over the body. The tip of the proboscis gradually turns green with white blotches. The eyestalks grow faster than the cephalic tentacles and soon become proportionately longer and wider. Approximately three weeks after metamorphosis, the strombids are morphologically similar to the adult snails, just smaller in size and shape of the shell. 

Locomotion of veligers in the plankton is via velar cilia for swimming and using the foot when crawling. When swimming, the velar lobes get extended and are directed away from the substratum and the foot lying between and slightly posterior to the velar lobes may move. Locomotion in veligers is via a gliding forward motion more similar to other gastropods, however small Leaping movements can be made at irregular intervals by throwing the shell forward and then sliding the foot forward. After metamorphosis the modal action pattern (MAP) of leaping is apparent within the first week, although gliding on the foot does still occur. Even the more primitive appearing species of Strombidae display this leaping movement. A possible explanation for the evolution of the Leap is that it may be the most economical way of moving a large shell across a sandy substrate. Alternatively, the Leap may reduce predation by presenting discontinuous visual and chemical stimuli to predators (Berg 1972).


Image of two specimens of Lentigo lentiginosus in their natural environment (Photographer: Asia Armstrong).

Courtship and Reproduction
Berg (1975) has described courtship and copulation in closely related strombid species; Strombus costatus, S. gigas and S. raninus. Courtship has been observed to consist of a repetitive follow-touch behaviour sequence. The male approaches the larger female from behind and places the anterior portion of his shell on top of her flaring lip, after following her trail from as far back as 5 metres.The female then remains stationary or moves away and this pattern is repeated until copulation takes place. Fertilization is internal, when the male extends his verge from under the flared shell and into the females genital region,posterior and to the right of the proboscis. The egg mass can start to form as the animals are copulating, whereby a fine thread of eggs pass down the genital canal on the right side of the foot and then up to the anterior edge of the propodium. The egg strands are layered by the movement backwards and forwards of the propodium and then the entire mass is pushed to the right side of the animal. These movements of the foot form a slight depression in the sand in front of the female, and the egg mass remains in this depression or is pushed to the right of it. From observations, females spend approximately 12 to 24 hours laying each egg mass and probably form more than one mass each reproductive season. Hatching occurs within approximately 100 hours from when the egg mass is laid down.