Invertebrate Movement

Topics: Animal, Mollusca, Cnidaria Pages: 5 (1540 words) Published: April 13, 2012
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How Do Sea Stars Move?
Each sea star had hundreds of tiny feet on the bottom of each ray. These are tube feet, or podia. These tiny feet can be filled with sea water. The vascular system of the sea star is also filled with sea water. By moving water from the vascular system into the tiny feet, the sea star can make a foot move by expanding it. This is how sea stars move around. Muscles within the feet are used to retract them.

Each ray of a sea star has a light sensitive organ called an eyespot. Though it can not see nearly as well as we do, sea stars can detect light and its general direction. They have some idea of where they are going. Sea Urchins & Sand Dollars

Sea urchins, heart urchins, cake urchins, and sand dollars belong to a sub-group of echinoderms called enchinoidea. These creatures have many sharp spines pointing out in all directions that offer protection from predators.

The spines are connected to the skeleton in a ball-joint manner called the "test." Spines are able to swivel towards a predator because they are connected to muscles.

These animals have five paired rows of tube feet with suckers. The mouth is on the bottom, and the anus on top. The mouth contains five teeth that point towards the center. The tubed feet are used to move along the bottom of the sea, where these organisms use their teeth to eat algae.

The word sponge, for most of us relates to the scrubbing sponge or a bath sponge. It is easy to forget that there is much more to sponges than the scrubbing and bath. The sponges are living animals that live in the water. They are stuck to the floor in the oceans, sea, and rivers. They are known as Porifera. The Poriferans are simple multi cellular animals. There are about 5000 to 10,000 of species of Porifera that are known today. Out of them only 150 species live in fresh water. The rest of the sponges dwell in salt-water. Sponges are very primitive creatures that evolved around 500 million years ago (1). There are many different types of sponges all over the world. Some of these sponges are very colorful and beautiful (1).

Common Name: Sponges
Kingdom: Animalia
Phylum: Porifera
Classes: Calcarea, Demospongiae, Hexactinellida
Sponges are the first and most simple members of Metazoa in the ancestral lineage of animals (Dawkins 2004). For a long time they were written off as ‘parazoa’. Today the rest of the Metazoans are considered to belong to Eumetazoa. Some molecular taxonomists think that there are two lineages of sponges, one more closely related to other more complex Metazoans than the other.

People often think of sponges as plants, rather than being animals. This misconception is due to some of the characteristics of the Porifera (Dawkins 2004). Like plants they do not move, i.e., they are sessile. They stay put in one place stuck to the bottom of the water- either salt or fresh. Also, they don't have muscles. Like plants they move at the cellular level (Dawkins 2004).



Worms are a common type of annelid
Annelids are invertebrates consisting of over 17,000 species of worms including ragworms, earthworms, and leeches. Annelids can be found in moist and wet earth, as well as marine and freshwater environments. Many annelids, such as leeches, are considered parasites. Annelids range in size from microscopic worms to the Australian Giant Gippsland Earthworm measuring up to 10 feet long. Annelid bodies are long, narrow, and tubular in shape, with multiple segments divided by ring-like constrictions. The front segment contains the brain, mouth and sensory system. The rear segment contains the anus. Some middle segments contain organs such as the circulatory system, digestive system, and nervous system. Segments grow one at a...
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