Annelida: Transport, Excretion, Respiration, Regulation, Nutrition, Reproduction, Development

Their habitat is usually freeliving or in soil and water. Annelids have bilateral symmetry. Some animals that are in the phylum annelida are any segmented worm, earthworms, leeches, and polychetes.

Click to see the dorsal vessel and ventral nerve cord

The following information is accurate according to our textbook, page 695 and 696.

Transport (Circulation)
Annelids have a closed circulatory system. That means that blood is stored in a group of blood vessels. In an earthworm, blood circulates through two major blood vessels that goes from the head to the toe. Blood in the dorsal vessel of the earthworm moves to the head. Blood in the ventral vessel of the worm moves from the head to the tail. In every body segment there are little blood vessels that connect the dorsal and ventral vessels and they supply the internal organs with blood.
Click to see earthworms circulatory system

Excretion
Annelids produce two kinds of wastes. There is digestive waste that exits the body through the anus at the end of the digestive tract. The second waste is cellular waste. The nitrogen in the waste is eliminated by nephrida, organ that filters fluids in the coelom.

Respiration
Annelids that live in water breathe through gills. Annelids that live on land, breathe in oxygen and give off carbon dioxide through their moist skin.

Regulation ( Nervous System)
Annelids have brains that are connected to the ventral nerve cord by circumpharyngeal connectives. The circumpharyngeal connectives run down each side of the pharynx. The palps, antennae, and cilia are used as sensory structures to feel all objects around it.

Nutrition
Annelids can be carnivorous, filter feeders, predators, or they can feed on vegetation.

Reproduction
Most annelids reproduce sexually. Some reproduce by external fertilization and have separate sexes. Other annelids are hermaphrodites. A single annelid rarely fertilizes its own egg. Usually two worms attach to eachother. After attaching, they would exchange sperm. Then the sperm would be stored in special sacs. When the eggs were ready to fertilize clitellum, specialized segments, would release a mucus ring where the eggs and sperm are relased. Then feritilization would occur in the ring. Afterward, the ring would slip off the worm's body and form a cocoon. Weeks after, baby worms would hatch.
Mating_earthworms1.jpg
Earthworms in sexual reproduction

Development
According to Frontiers in Zoology, annelida embryos undergo a process called spiral cleavage to form a blastula, early stage of embryotic development. After this, the annelida goes into a process where the germ layers of an embryo are formed and the body plan of the mature organism is established. Then the blastopore is formed. The blastopore elongates then two openings that later develop into the mouth and anus.
Blastulation.png
Blastulation