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: Covered with papillae.
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.