María Paula Vélez R.

INVERTEBRATES REPRODUCTION

Some characteristics

Of the million or more animal species in the world, more than 98% are invertebrates. Invertebrates don't have an internal skeleton made of bone. Many invertebrates have a fluid-filled, hydrostatic skeleton, like the jelly fish or worm. Others have a hard outer shell, like insects and crustaceans.

There are many types of invertebrates. The most common invertebrates include:

• Sponges• Cnidarians• Worms (flat, round and segmented)• Mollusks• Arthropods • Echinoderms.

Invertebrates Reproduction

Reproduction in invertebrates differs depending on species. Asexual reproduction (having no sex or sexual organs) is quite common, however, sexual reproduction is more typical.

Hermaphrodites are common in invertebrates, this means that both male and female sexual organs are present in one individual.

In single sex species, where only one sexual organ is present, males and females do not have to make contact to reproduce as fertilization can occur externally.

Some types of asexual reproduction

in invertebrates

1. Fragmentation: The breaking of the parent body into several pieces. Regeneration follows fragmentation.

2. Fission: The individual separates into two or more individuals of about equal size.

sea annemone

3. Budding: The splitting of new individuals from existing ones.

Bud

Sexual reproduction in invertebrates

External fertilization• Union of the gametes outside the body of the mother.

• Occurs mostly in wet environments and requires both the male and the female to release their gametes into their surroundings (usually water).

• An advantage of external fertilization is that it results in

the production of a large number of offspring.

• One disadvantage is that environmental hazards such as predators greatly reduce the chance of surviving into adulthood.

Internal fertilization

• Union of the gametes inside the body of the female, the sperm having been transferred from the body of the male by an accessory sex organ or other means.

Hermaphroditic organisms

• Animal or plant that normally possesses both male and female reproductive systems, producing both eggs and sperm.

• Some parasitic species, e.g., the tapeworm, are self-fertile as well as hermaphroditic, insuring reproduction where the parasite may be the only member of its species in the host.

LIFE CYCLES AND METAMORPHOSIS