Aboral
in a direction away from the mouth; the part of the body opposite the mouth

Anal Cone
in crinoids and echinoids, a fleshy projection bearing the anus at its apex; also known as an anal tube

Apical System
in echinoids, a ring of specialized skeletal plates, including the genital plates and ocular plates; usually located on the highest point of the test

Arm
in asteroids, crinoids, and ophiuroids, a movable, jointed ambulacral projection, distal to the disk or calyx that carries a radial branch of the water vascular system and the nervous system; sometimes called a ray

Basket
one of several types of microscopic skeletal ossicles in holothuroids; minute cup-shaped ossicle, usually with four projections

Button
one of several types of microscopic skeletal ossicles in holothuroids; minute ossicle with four perforations; may be smooth or knobbed

Disk
the round or pentagonal central body region of ophiuroids and asteroids; see also Terminal Disk

Distal
in a direction away from the center of the body; for example, toward the tip of the arm in asteroids or the tip of a spine in echinoids

Dorsal
in echinoderms, this term is variously applied; in asteroids, ophiuroids and echinoids it usually refers to the surface of the body that is opposite the mouth, the surface that is uppermost; in holothuroids, with mouth and anus opposite ends of the cylindrical body, the uppermost surface is considered dorsal; in crinoids, the surface opposite the mouth in considered dorsal by convention, even though it is functionally the ventral (lower) side

Echinulate
something spiny or prickly, usually referring to the microscopic texture of a skeletal element such as a spine

Hermaphrodism
a condition in organisms whereby one individual possesses both functional male and female reproductive structures; hermaphroditic individuals may express both sexes simultaneously, alternately, or sequentially

Interambulacral Area
an oral or aboral section of the body lying between two ambulacra; in interradius; also known as an interambulacrum

Interradial
referring to interambulacral areas of the body; interradius and interradii also commonly used

Oral
in a direction toward the mouth; a part of the body on the same surface as the mouth

Oral Papillae
in ophiuroids, small plates at the edge of the mouth, attached to the edges of the jaw plate and/or to the aboral shield; may be variously shaped, from spine-like to scale-like

Papillae
in holothuroids, specialized dorsal tube feet that lack a suckered tip; in ophiuroids, certain skeletal elements of the jaws or disk

Papillate / Papillose
covered with papillae

Pedicellariae
small stalked or unstalked pincer-like organs on the body of asteroids and echinoids, used for defense and grooming

Peltate
shield-shaped; used to describe the tentacles of some holothuroids

Perforated Plate
one of several types of microscopic skeletal ossicles in holothuroids; sieve-like and widespread; may also be found in other echinoderm classes, especially in juvenile individuals

Periproct
in echinoids, a flexible region surrounding the anus, which consists of a membrane containing embedded plates and often bearing spines and pedicellariae

Plates
one of several types of skeletal elements in echinoderms; tabular structures with a characteristic shape and a fixed position

Primary Plates
the first-formed plates on the dorsal side of the disk; in ophiuroids, these are the central and five radial plates; in adults, they may form a rosette of scales near the center of the disk, or they may be separated by numerous secondarily developed scales

Radial
in a direction toward the central axis of an arm or ambulacrum; a part of the body near an arm or ambulacrum

Radial Shields
pairs of plates on the dorsal surface of the ophiuroid disk, which lie near the base of each arm; usually relatively large and conspicuous, but may be hidden by granules or superficial scales

Rods
one of several types of microscopic skeletal ossicles in holothuroids; commonly found as supporting structures in tentacles or tube feet

Scales
one of several types of skeletal elements in echinoderms; flat, thin structures that are overlapping, tessellate, or haphazardly arrayed

Sole
in some holothuroids, the flattened ventral part of the body, either covered with or surrounded by tube feet

Spines
one of several skeletal elements in echinoderms; movable, articulating structures that are long, slender and attenuated

Teeth
in ophiuroids, small plates or spines attached to the dental plate on the inner edge of the jaw, a series of them extending into the mouth; in echinoids, the five hard, sharp, and movable ossicles incorporated in Aristotle’s lantern; the term also refers to five movable ossicles that surround the anus of some holothuroids

Tentacle Scales
small, movable spines or scales, associated with ophiuroid tube feet, which are attached to the ventral arm plate and/or lateral arm plate; may cover the tentacle pores and protect the retracted tube feet

Tentacles
in holothuroids, feeding structures in the form of highly modified tube feet arranged in a ring around the mouth

Terminal Disk
round portion on the end of the tube foot in many echinoderms; usually employed for attachment to substrates

Tube Feet
fluid-filled, fingerlike extensions of the water vascular system that protrude through the openings in the skeleton or between skeletal elements; muscles and nerves in the shaft of the tube feet control their movements; glands, and sometimes a muscular sucker, at the tip function in adhesion; specialized tube feet are used for locomotion, feeding, burrowing, respiration, and a combination of functions

Ventral
in echinoderms, this term is variously applied; in asteroids, echinoids and ophiuroids, it is the surface of the body that carries the mouth; this surface is in contact with the substrate; in holothuroids, with mouth and anus at opposite ends of a cylindrical body, the ventral surface is lowermost, in contact with the substrate; in crinoids, the ventral surface carries the mouth and is functionally the uppermost surface