Invertebrates, Mollusks, Arthropods and Echinoderms
Science

An invertebrate with an exoskeleton, jointed legs, and segmented body, like any insect, spider, crab etc
Arthropod
An invertebrate with an exoskeleton, jointed legs, and segmented body, like any insect, spider, crab etc. arthropod. An arthropod is an animal with a hard outer shell and multiple jointed legs.

Body plan composed of two halves which are mirror images of each other
Bilateral symmetry
Body plan composed of two halves which are mirror images of each other. Bilateral symmetry. In science, bilateral symmetry means that if you draw a line down the middle of a living organism, both sides look the same.

A circulation system in which blood flows within a network of vessels
Closed circulatory system
A circulation system in which blood flows within a network of vessels. Closed circulatory system. In a closed circulatory system, blood moves through a series of tubes called vessels, delivering nutrients and oxygen efficiently throughout the body.

A marine invertebrate with an internal skeleton and a water vascular system, like a starfish
Echinoderm
A marine invertebrate with an internal skeleton and a water vascular system, like a starfish. Echinoderm. An echinoderm is a sea creature with a spiny skin and a system that uses water to help it move and feed.

The immature form of an animal, it looks very different from the adult form
Larva
The immature form of an animal, it looks very different from the adult form. Larva. In simple terms, a larva is the early stage of an animal's life cycle, often looking nothing like the adult, and eventually transforming as it grows.

A system in which blood moves through open spaces as well as vessels
Open circulatory system
A system in which blood moves through open spaces as well as vessels. Open circulatory system. In an open circulatory system, blood flows freely around the body's organs instead of being contained entirely within blood vessels.

A tube-shaped organism usually attached to a surface, it is a life stage of a cnidarian
Polyp
A tube-shaped organism usually attached to a surface, it is a life stage of a cnidarian. Polyp. A polyp is a small, sessile life stage of some marine animals like jellyfish and corals, often resembling a small tube with tentacles.

Hollow tubes that end in suction cups, echinoderms use them to move and collect food
Tube feet
Hollow tubes that end in suction cups, echinoderms use them to move and collect food. Tube feet are small, flexible, and extendable appendages on the underside of starfish and sea urchins that help with movement and feeding.