How are they classified?
Describes the balanced distribution of an animal's parts around an axis.
symmetry
An invertebrate with a hollow body, many small pores, and a large opening at the top.
sponge
An animal with a soft, unsegmented body; bilateral symmetry; and a body divided into a head, foot, mantle.
mollusk
An invertebrate that has a segmented body, an exoskeleton, and jointed appendages.
arthropods
When the right and left body parts of an organism are arranged the same way.
bilateral symmetry
The flexible, fibrous substance that makes up the body of a sponge.
spongin
The fleshy tissue that covers and protects the mollusk's internal body parts.
mantle
An external skeleton. Usually made from chitin or calcium.
exoskeleton
When the body parts of an organism are arranged in a circle around a center point.
radial symmetry
The process of growing new body parts.
regeneration
A mollusk that has a shell of two halves, or valves
bivalve
A jointed, moveable, sensory structure on the head of arthropods.
antenna
When the body is shaped irregularly and cannot be split into equal parts.
asymmetry
The group of invertebrates that have radial symmetry and tentacles with stinging cells.
cnidarian
An internal skeleton. Usually made of calcium or silia.
endoskeleton
A transformation in insects that involves four stages: egg, larva, pupa, and adult.
complete metamorphosis
The name given to a segmented worm.
annelid
A system of water-filled canals inside an echinoderm.
water-vascular system
A transformation in insects that involves three stages: egg, nymph, and adult.
incomplete metamorphosis