Echinoderms

Some General Characteristics

Echinoderms are marine invertebrates with the following characteristics:

• The adults have 5-parted radial symmetry and the larvae have bilateral symmetry. Echinoderms evolved from an ancestor with bilateral symmetry and are considered to be bilateral animals.
• They have separate holes for a mouth and an anus. In adult animals that have upper and lower body surfaces, the upper surface is referred to as the aboral surface and the lower surface or underside is called the oral surface. The mouth is typically found in the middle of the oral surface.
• Most echinoderm taxa are dioecious (each individual is either male or female; i.e., some individuals are male [and produce sperm] and other individuals are female [and produce eggs])
• They have an internal skeleton, located below the epidermis. The skeleton consists of collagen-containing connective tissue that is embedded with calcareous skeletal pieces (ossicles).
• Echinoderms are the only animals known to be capable of rapidly changing the flexibility of their connective tissue (i.e., from rigid to flexible or vice-versa). They are said to have mutable (or catch) connective tissue.
• They possess a water vascular system, which may be used for movement, attachment, feeding or other purposes.

Echinoderms found in New England

• Family: Echinarachniidae   Echinarachnius parma (Sand Dollar)

• Family: Strongylocentrotidae   Strongylocentrotus droebachiensis (Green Sea Urchin)