Veliger (from Latin velum - “sail” and gero - “bear”), or sailboat - the pelagic form of mollusk larvae of the classes Scaphopoda , Bivalvia and Gastropoda . Veligers are part of free-floating plankton . A characteristic feature of veligers is velum - formations resembling ciliated lobes. They serve for movement and nutrition.
Nutrition
The larval phase begins with the laying of eggs and continues until the metamorphosis of adulthood. Veliger feeds with cilia, while different cilia perform different functions. Some cilia direct food into the mouth, while others repel foreign objects. By the method of nutrition, two forms of veligers are distinguished - planktotrophs and lecithotrophs. Mollusks of the same species can produce larvae with different types of food, but, nevertheless, they develop into morphologically identical individuals. Individuals with different types of larval development can mate with each other.
Planktotrophic feeding means that the animal eats free-floating planktonic organisms. Planktotrophic larvae hatch from smaller eggs, and their proportion in the clutch is larger. Veligers eating this way remain larvae longer. The long larval period is unfavorable for them, as mortality increases, and the probability of surviving to metamorphosis and becoming a mature adult decreases.
Lecithotrophic larvae feed on the supply of nutrients contained in the egg itself, without consuming any other food before metamorphosis. Although usually larvae feed only in one way, there are also lecithotrophic veligers that additionally feed on the planktotrophic method, for example, Phestilla sibogea .
Metamorphosis
Metamorphosis can last up to two days. At this time, large morphological changes occur, and the larva finally adapts to the habitat in the benthos . During metamorphosis, organs such as the anterior sensory organ and velum disappear. At first, the velum fights unevenly, and the cilia fall away from it. Then the velum is absorbed. The larva acquires its final form in metamorphosis, forming for this also some (depending on the species) missing organs.
Literature
- Biological Encyclopedic Dictionary / Ch. ed. M.S. Gilyarov ; Editorial: A.A. Baev , G.G. Vinberg, G.A. Zavarzin et al. - M .: Sov. Encyclopedia , 1986.- S. 90.- 831 p. - 100,000 copies.