Reproduction Mollusca

trochophore larva

the simplest molluscan reproductive system relies on external fertilization, more complex variations. produce eggs, may emerge trochophore larvae, more complex veliger larvae, or miniature adults. 2 gonads sit next coelom, small cavity surrounds heart, shed ova or sperm. nephridia extract gametes coelom , emit them mantle cavity. molluscs use such system remain of 1 sex lives , rely on external fertilization. molluscs use internal fertilization and/or hermaphrodites, functioning both sexes; both of these methods require more complex reproductive systems.

the basic molluscan larva trochophore, planktonic , feeds on floating food particles using 2 bands of cilia around equator sweep food mouth, uses more cilia drive them stomach, uses further cilia expel undigested remains through anus. new tissue grows in bands of mesoderm in interior, apical tuft , anus pushed further apart animal grows. trochophore stage succeeded veliger stage in prototroch, equatorial band of cilia nearest apical tuft, develops velum ( veil ), pair of cilia-bearing lobes larva swims. eventually, larva sinks seafloor , metamorphoses adult form. while metamorphosis usual state in molluscs, cephalopods differ in exhibiting direct development: hatchling miniaturized form of adult.