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Marine Invertebrate Zoology

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Asexual reproduction

Reproduction in the absence of fertilization (without union of gametes)

Parthenogenesis

Parthenogenesis – eggs develop to adulthood in the absence of fertilization (some arthropods, and rotifers)

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Parthenogenesis

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Sexual Reproduction

Patterns of Sexuality– Gonochoristic or

dioecious The parents are of 2

different sexes

Hermaphroditism – both male and female sex organs

– Simultaneous or sequential

– Protandric– Protogynous

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Getting the “Boys” to the Party

Internal fertilization– Direct – Indirect

Methods of transfer vary across phyla

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Sexual Reproduction

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Broadcast Spawning & External Fertilization

Requires the precise timing of gamete release

Successful fertilization is dependent on:

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Larval Forms

The product of external and some internal fertilization usually results in a free-living, swimming larvae that grows and differentiates in the plankton

– Most larvae are ciliated for locomotion, and food collection

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Advantages for Free-living Larvae

Transitions between phases of complex life cycles usually requires metamorphosis (abrupt morphological, physiological, and ecological changes)

Cost of Delaying Metamorphosis

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