Here's a concise summary of Bivalve Reproduction:
*Sex Determination:*
1. Dioecious (two sexes): majority of bivalves
2. Hermaphroditic (one sex): few bivalves (e.g., Cockles, Poromyidae, some oysters, scallops, freshwater clams)
*Reproductive Organs:*
1. Gonads: closely situated, surrounding intestinal loops
2. Gonoducts: simple, no copulation
*Reproductive Process:*
1. Protobranchs and Filibranchs: gonoducts open into nephridia
2. Eulamellibranchs: gonoducts open into mantle cavity near nephridiopore
3. Sperm and eggs released into surrounding water (most bivalves)
4. Fertilization:
- External (most bivalves)
- Internal (some bivalves, e.g., Ostrea edulis L.)
- Self-fertilization (some freshwater hermaphrodites)
*Egg Development:*
1. Fertilized eggs develop in gill filaments (some bivalves)
2. Eggs travel into water tubes of gill (some freshwater hermaphrodites)
3. Larval development
*Key Features:*
1. Simple gonoducts
2. No copulation
3. External fertilization (most bivalves)
4. Internal fertilization (some bivalves)
*Examples of Hermaphroditic Bivalves:*
1. Cockles (Cardiidae)
2. Poromyidae
3. Some oysters (Ostrea edulis L.)
4. Scallops (Pectinidae)
5. Freshwater clams (Sphaeriidae, Unionidae)
*Gamete Formation:*
1. Gonad development: gonads produce sperm and eggs.
2. Spermatogenesis: sperm formation.
3. Oogenesis: egg formation.
*Mating and Fertilization:*
1. External fertilization: sperm and eggs released into water.
2. Internal fertilization: sperm drawn into suprabranchial chamber (some bivalves).
3. Self-fertilization: occurs in genital ducts (some freshwater hermaphrodites).
*Egg Development:*
1. Fertilized eggs develop in gill filaments (some bivalves).
2. Eggs travel into water tubes of gill (some freshwater hermaphrodites).
3. Embryonic development.
*Larval Development:*
1. Trochophore larva: initial larval stage.
2. D-veliger larva: develops from trochophore.
3. Pediveliger larva: final larval stage.
*Settlement and Metamorphosis:*
1. Larvae settle on substrate.
2. Metamorphosis: transformation into juvenile bivalve.
*Hormonal Regulation:*
1. Gonadotropin-releasing hormone (GnRH): regulates gamete formation.
2. Estrogen and testosterone: regulate reproductive processes.
*Neural Control:*
1. Nervous system regulates gamete release.
2. Neural signals control reproductive behavior.
*Environmental Influences:*
1. Water temperature: influences gamete formation and larval development.
2. Food availability: affects reproductive success.
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