Terminology Description
Terminology Description
Abactinal The area of the body opposite the mouth. Aboral in a direction away from the mouth; the part of the body opposite the mouth
Accessory dorsal arm plate In some ophiuroids, one or several small, symmetrically arranged plates that are inserted between the dorsal arm plate and the lateral arm plate.
Actinal The surface of the body that contains the mouth.
Adambulacral Towards, or immediately adjacent to, an ambulacrum.
Adapical In echinoids, towards the highest part of the test.
Adoral shields In ophiuroids, a pair of plates, one of which is found at each side of the oral shield.
Adpressed Squeezed against. The adpressed arm spines of ophiuroids are flattened against the sides of the arm.
Alcareous ring A ring of large ossicles surrounding the holothurian esophagus. It forms a point of insertion for longitudinal muscles and, when present, retractor muscles.
Ambulacral Groove In asteroids, the groove on the oral (ventral) surface of the arm, in which the tube feet are carried. Its sides are formed by the adambulacral plates, and it is roofed by the ambulacral plates. In crinoids, a furrow on the oral (dorsal) surface of the pinnules, arms, and central body, which is lined with cilia and bordered by the tube feet.
Ambulacrum A zone of the body that carries tube feet. Echinoderms generally have 5 ambulacra. The midline of an ambulacrum is a radius.
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
Apodous (apodan) Lacking tube feet, in reference to holothurians.
Appendage A tube foot, spine, pedicellaria, or arm of an adult, or a projection from the larval body. In holothuroids, the tube feet may be modified to form a papilla lacking terminal suckers.
Arm Joint In ophiuroids, one of a series of articulating units comprising the arm, consisting of an internal vertebral ossicle, surrounding dorsal, lateral and ventral arm plates, and associated structures.
Arm length A body dimension of an ophiuroid measured from the edge of the disc to the tip of an arm.
Arm spines Spines attached to the lateral arm plate in ophiuroids, and to the marginal plates in asteroids.
Arm In asteroids, crinoids and ophiuroids, a moveable, jointed ambulacral projection, distal to the disc or calyx, that carries a radial branch of the water vascular system and the nervous system. Sometimes called a ray.
Armament A general term which describes an echinoderm’s array of spines and/or pedicellariae.
Asexual reproduction Reproduction that occurs without the fusion of male and female gametes, usually by splitting of the body into two parts that regenerate. The genetically identical offspring of asexual parents are a clone.
Autoevisceration In holothuroids, expulsion of the digestive tract and associated organs through the anus; in some species, the anterior end of the body ruptures and the calcareous ring and associated organs are expelled. Believed to be a defensive mechanism.
Autotomy A defensive process of self-mutilation initiated in response to adverse stimuli. It involves loss of portions of the body, such as the arms or disc in ophiuroids.
Basal In crinoids, one of a circlet of five plates that form part of the calyx.
Basket One of several types of microscopic skeletal ossicles in holothuroids; minute cup-shaped ossicle, usually with four projections
Baskets (CUPS) Are minute cup-shaped ossicles usually with four perforations.
Bilateral symmetry A pattern of symmetry, based upon an anterior-posterior axis, in which the left side of the body is a mirror image of the right side.
Bipinnaria A free-swimming larval stage of asteroids. Bipinnaria larvae have blunt larval appendages which support a ciliated band. The bipinnaria either may develop into a BRACHIOLARIA larva, or it may undergo metamorphosis during which the juvenile arises on the left side of the larval body.
Brooding Reproductive mode in which the embryos are protected on, in, or beneath the parent, and emerge as tiny, crawl away juveniles.
Buccal Lying within the mouth.
Bursa In ophiuroids, an organ within the disc formed by an inpouching of epidermis. Bursae function as respiratory structures and are associated with the gonoducts. They house the developing embryos of brooding species.
Bursal slit The opening of a bursa, located on the ventral interradius of the disc at the base of the arm. There generally is one bursal slit on each side of an arm.
Buttons Are minute, flat, with few perforations; they may be smooth or knobbed. Solid, irregularly-shaped miliary granules are found in the body wall and muscles of apodous holothuroids. Sieve-like perforated plates are widespread in holothuroids, and may be found in other echinoderm classes, especially in juvenile individuals. RODS are commonly found as supporting structures in tentacles or tube feet.
Calcite The mineral form of calcium carbonate that makes up the echinoderm skeleton.
Calyx The cuplike central portion of the crinoid body, which supports the arms and visceral mass.
Carinal Plates In asteroids, plates forming a keel or ridge along the abactinal surface of an arm.
Centrodorsal The middle ossicle attached to the aboral surface of the crinoid calyx; commonly carries cirri.
Cidaroids A subclass of echinoids which arose in the Triassic; typified by species that have few, large, solid spines.
Cirri The unbranched, jointed appendages arising from the crinoid centrodorsal; they are used for attachment to the substratum.
Cloaca In holothuroids, the posterior part of the intestine; it carries the openings to the respiratory trees and cuvierian tubules, when present.
Commensal An organism that lives in association with another organism, and which usually benefits from the partnership without harming its host.
Congeners The species belonging to a single genus.
Crenulate Grooved; refers to the ribbed edge of certain echinoid tubercles.
Cuvierian Tubules Defensive structures of some holothurians, discharged through the anus as sticky threads which entangle and discourage predators.
Dendritic Branching in a tree-like manner, as in certain holothuroid tentacles.
Dental Papillae A cluster of small, blunt, spinelike structures on the dental plate, near the ventral tip of the jaw.
Dermis The stratum of cells beneath the epidermal covering of the body wall. In echinoderms, the skeleton develops in the dermis and is filled with dermal tissue.
Digitate Fingerlike, or carrying fingerlike structures; applied to certain holothuroid tentacles.
Disc diameter A body dimension of an ophiuroid measured from the distal edge of a pair of radial shields to the disc edge in the opposite interradius.
Disc The round or pentagonal central body region of ophiuroids and asteroids
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 Arm Plate A plate on the aboral surface of an ophiuroid arm joint; one of the plates on the aboral surface of an asteroid arm.
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 at opposite ends of a cylindrical body, the uppermost surface is considered dorsal. In crinoids, by convention, the surface opposite the mouth is considered dorsal even though it is functionally the ventral (lower) side.
Echinopluteus The free-swimming larval stage of an echinoid. Echinoplutei have appendages that are supported by skeleton, and that bear ciliary bands. The process of metamorphosis in which a juvenile echinoid arises from a rudiment on the left side of the echinopluteus body is completed in only a few minutes.
Echinulate Something spiny or prickly, usually referring to the microscopic texture of a skeletal element such as a spine
Embryo An early developmental stage that is enclosed in a fertilization membrane or protected by the body of the parent. It transforms into a juvenile through metamorphosis.
EPT (= Expanded Peripheral Trabeculae) Microscopic, transparent nodules on the surface of skeletal plates. In ophiocomid ophiuroids they are a component of a photoreceptor system.
Fascioles In many Irregular Echinoids, narrow bands of small, specialized spines; visible on the denuded test as bands of densely packed, tiny tubercles. Fascioles provide a flow of water to aid in respiration.
Fence Papillae Peg-shaped spinelets fringing the edge of the disc of Ophiophragmus species.
Fission Asexual reproduction by splitting of the body into two parts, each of which regenerates into a complete animal.
Food Groove In crinoids, furrows lined with cilia, which conduct particles of food from the pinnules to the arms, and then on to the mouth.
Fusiform Shaped like a spindle, broadest in the middle and tapering towards each end.
Gametogenesis The process of formation of reproductive cells, eggs, and sperms.
Genital Papilla In ophiuroids, granules or spinules attached to the edge of the bursal slit. The term is also used (perhaps more appropriately) for the fleshy outlets of the gonoducts in ophiuroids that lack bursae, and in some echinoids. In holothuroids, a single, fleshy genital papilla opens to the exterior on the dorsal surface of the body immediately posterior to the tentacles.
Genital Pinnule In crinoids, a pinnule that is distal to the oral pinnules that contains gonad tissues.
Genital Plate In ophiuroids, a bar-like ossicle connecting the radial shield to the arm and supporting the radial edge of the bursal slit.
Globiferous Pedicellaria A three-valved echinoid pedicellaria that is equipped with venom sacs.
Gonoduct Genital duct. A duct which carries eggs or sperms from the gonad to an external genital opening..
Granules That are minute and nearly equidimensional,
Heart Urchin A more or less heart-shaped burrowing echinoid, usually in the order Spatangoida.
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
Hooks Minute, moveable, crescentic ossicles that articulate with the dorsal arm scales in gorgonocephalid ophiuroids (other ophiuroids may have hook-shaped arm spines attached to the lateral arm plates).
Inferomarginals In asteroids, a row of plates that define the ventral edge of the body; inferomarginals are overlain by a row of superomarginals.
Infradental Papillae In amphiurid ophiuroids, a pair of small, blocklike plates attached at the ventral tip of the jaw, below the teeth.
Interambulacral Area An oral or aboral section of the body lying between two ambulacra; in interradius; also known as an interambulacrum
Interambulacrum An oral or aboral sector of the body lying between two ambulacra. An interradius.
Interradial (Interradius, Interradii) Referring to interambulacral sectors of the body.
Interradial Referring to interambulacral areas of the body; interradius and interradii also commonly used
Introvert In some holothurians, the anterior of the body including tentacles and associated structures. It can be withdrawn into the body by means of retractor muscles.
Irregular Echinoid A heart-shaped or disc-shaped echinoid, usually covered with very short spines, generally living in or on soft sediment. Irregular echinoids have some degree of bilateral symmetry, as the anus is not at the center of the dorsal surface.
Jaw A moveable triangular structure that extends into the mouth in ophiuroids and asteroids. In the latter group, it is also referred to as a mouth-angle plate.
Labrum A posterior or lower projection of the border of the mouth in irregular echinoids.
Lappets In crinoids, small moveable plates that support the tube feet and form a protective covering over the food grooves.
Larva An early developmental stage that is independent of the fertilization membrane and the parent. Through metamorphosis it transforms into a juvenile.
Lateral Arm Plates In ophiuroids, paired plates covering the sides of each arm joint and bearing the arm spines.
Lecithotrophy A mode of reproduction in which free-swimming larvae develop using nutrient laid down in the egg. Lecithotrophic larvae do not feed on particulate matter, but they may supplement yolk reserves by the uptake of nutrients dissolved in seawater.
Lunule A slit in the echinoid test, as in the five or six-holed sand dollars.
Madreporite A plate with numerous perforations that is connected to the watervascular ring by a so-called stone canal. In most holothuroids it is internal. In asteroids and echinoids it opens to the exterior on the dorsal surface of the body; in ophiuroids it opens on the ventral surface, near the mouth. Crinoids lack a madreporite, having instead a series of small pores in the tegmen, opening to the body cavity.
Marginals In asteroids, plates covering the sides of the arms.
Ocular Plate A plate in the apical system of echinoids. The five ocular plates are radial (ambulacral) in position, and new ambulacral plates develop at their distal edges. In asteroids, the most distal plate of the arm, enclosing the terminal tube foot.
Ophiopluteus The free-swimming larval stage of an ophiuroid. Ophioplutei have appendages that are supported by skeleton and bear ciliary bands. During metamorphosis, the juvenile ophiuroid develops from a rudiment on the ventral surface of the larva; the process may involve resorption or loss of parts of larval structures.
Optic cushion A pigmented light-sensory structure of asteroids, projecting from the base of the ventral surface of the terminal tube foot.
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
Oral Shield A relatively large plate at the distal end of the ophiuroid jaw. At least one of the oral shields is modified as a madreporite.
Oral Tentacles In ophiuroids, tube feet inside the mouth, arising from the jaws.
Oral In a direction toward the mouth; a part of the body on the same surface as the mouth
Ossicle types In holothuroids, the various types of microscopic skeletal ossicles can be broadly classified, based on their shapes. The shanks of fluked anchors are associated with shield-shaped anchor plates in the body wall of synaptid holothuroids.
Ossicle A small, usually microscopic skeletal element, embedded in integument. Commonly found in the body wall of holothurians, but also known from the body wall and body cavity tissues of other echinoderms (e.g., the ophiuroid stomach) and the tube feet of echinoids and asteroids. The term is sometimes used to refer to all skeletal elements, especially in crinoids.
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
Papulae Small, soft, retractable extensions of the body cavity that project through pores in the body wall of asteroids; used for respiration. Papulae may be finger or glove-shaped, and are sometimes arrayed in dense patches.
Paxillae In some asteroids, columnar plates that bear an apical cluster of spinelets or granules.
Paxillate In asteroids, carrying paxillae.
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
Penicillate Tube Foot In some echinoids, a long, extensible tube foot bearing a brush-like array of glandular projections at the tip.
Pentactula The post-metamorphic developmental stage of holothuroids with either planktotrophic or lecithotrophic larvae. It has an anterior mouth and buccal podia, and one or two tube feet.
Perforate Tubercle In echinoids, a primary or secondary tubercle with an apical perforation for the insertion of a ligament.
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
Peripetalous In echinoids, refers to a fasciole which runs around the distal extremities of the anterior and posterior petals (ambulacra I, II, IV, V) and crosses ambulacrum III.
Periproct In echinoids, a flexible region surrounding the anus, which consists of a membrane containing embedded plates and often bearing spines and pedicellariae
Peristome In echinoids, the area of the test which carries the mouth. The surrounding peristomial membrane is commonly plated.
Perradial In echinoids, having a meridional position at the midline of an ambulacrum.
Pinnate Feather-like.
Pinnular Comb A group of modified pinnulars (see PINNULE) of an oral pinnule, which has a comblike profile. Present in Comasteridae and some Antedonidae.
Pinnule In crinoids, an unbranched appendage arising from a brachial ossicle and composed of a series of pinnular ossicles.
Planktotrophy The mode of development of free-swimming larvae that feed on particulate matter. Planktotrophic larvae grow using nutrients obtained from the plankton.
Plates One of several types of skeletal elements in echinoderms; tabular structures with a characteristic shape and a fixed position
Polian Vesicle Fluid-filled sacs attached to the water-vascular ring. They act as resevoirs, holding fluid that is displaced when tube feet contract.
Polyporous In echinoids, a compound ambulacral plate with many pore pairs, usually five or more.
Pore Pair Ambulacral pore divided by a skeletal wall, through which a single tube foot passes.
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
Primary Spines In echinoids, the first-formed, larger spines; carried on primary tubercles in ambulacra and interambulacra.
Proximal Towards the center of the body. R. A body dimension of an asteroid, the major radius, measured from the center of the disc to the tip of the longest arm. r. A body dimension of an asteroid, the minor radius, measured from the center of the disc to the edge of the disc in the middle of an interradius.
Radial Shields Pairs of plates on the dorsal surface of the ophiuroid disc, which lie near the base of each arm. They are usually relatively large and conspicuous, but may be hidden by granules or superficial scales.
Radial Symmetry A pattern of symmetry in which identical segments of the body are arranged around a central axis. Echinoderms generally have a five-part (pentamerous) radial symmetry.
Radial In a direction toward the central axis of an arm or ambulacrum; a part of the body near an arm or ambulacrum
Regular Echinoid A more or less spherical echinoid, with long spines, and with the anus situated at the center of the aboral surface. Typically lives on hard bottoms, or among marine plants.
Respiratory Trees Paired respiratory organs of some holothuroids. They are attached to the cloaca, just inside the anus, and project anteriorly in the body cavity.
Retractor In holothurians, one of five muscles which act to pull the tentacles into the safety of the buccal cavity.
Rheophilic Literally, "current-loving." Rheophilic organisms prefer habitats with significant water movement. Rheophobic organisms avoid currents, and occupy sheltered positions or are restricted to low-energy habitats.
Rods One of several types of microscopic skeletal ossicles in holothuroids; commonly found as supporting structures in tentacles or tube feet
Rosette Modified basal ossicles of some crinoids; a microscopic ossicle of some holothuroids. Scrobicular. In echinoids, surrounding the base of a spine.
Scales One of several types of skeletal elements in echinoderms; flat, thin structures that are overlapping, tessellate, or haphazardly arrayed
Secondary Spines In echinoids, the smaller spines carried on secondary tubercles in the ambulacra and interambulacra.
Sensory Cup A stalked cup-like sensory organ on the tentacle stems of some holothuroids.
Skeletal Elements Supporting and protective dermal structures consisting of a calcite meshwork (stereom) and invested with a thin layer of tissue (stroma).
Sole In some holothuroids, the flattened ventral part of the body, either covered with tube feet or surrounded by feet.
Sphaeridia Orientation organs generally situated near the mouth of echinoids, consisting of a tiny spine with a swollen tip, set in a pit or a closed chamber.
Spinelets That are enlarged, elongate cylindrical, or angular granules (this term is sometimes applied to small spines)
Spines Are moveable, articulating structures that are long, slender, and attenuated. Small structures fixed to the surface of scales or plates include
Spinules That have various numbers of pointed apical projections (e.g. bifid, trifid, multifid). Also fixed, and relatively larger than granules, are small structures referred to as stumps, which are usually prickly, and tubercles which are smooth and more massive.
Statocyst In some holothurians, a sensory organ of balance, consisting of a hollow sphere lined by sensory receptor cells, which contains moveable granules.
Stone canal A tube, usually reinforced with ossicles, leading from the madreporite to the water-vascular ring canal.
Superomarginals In asteroids, a row of plates defining the dorsal edge of the body. They overlie a row of inferomarginals
Tables Consist of a basal perforated disc and a central spire composed of three or more rods joined by crossbars.
Tabulate Spines with a flat upper or distal surface.
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
Tegmen The surface of the crinoid visceral mass that bears the mouth and confluent food grooves leading to the arms, as well as the anus. It may be naked or reinforced with ossicles or plates.
Tentacle Pore In ophiuroids, an opening between the ventral arm plate and the lateral arm plate, through which a tube foot projects. Each arm joint has two tentacle pores.
Tentacle Scales Small, moveable spines or scales, associated with ophiuroid tube feet, which are attached to the ventral arm plate and/or lateral arm plate. Tentacle scales 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 Disc Round portion on the end of the tube foot in many echinoderms; usually employed for attachment to substrates
Test The "shell" of an echinoid, made up of many small skeletal plates. A "naked" test is one from which soft tissue, and projecting structures such as spines, have been removed. This process occurs naturally after the death of a sea urchin. To identify some urchins, it is necessary to clean a portion of the test with bleach, to see the underlying plates.
Trifid Divided into three parts. Regarding "trifid spinule"
Trigeminate An echinoid ambulacral plate, have three pore-pairs.
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
Tubercle A rounded prominence on the skeleton. In echinoids and some asteroids, a spine articulates with a tubercle.
Tuberculated Carrying numerous tubercles.
Ventral Arm Plate A plate on the oral surface of each ophiuroid arm joint; one of the plates on the oral surface of an asteroid arm.
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 the 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.
Vermiform Worm shaped.
Vertebra An internal ossicle within every ophiuroid arm joint, connected by ligament and muscle to the vertebrae of adjacent joints. It is so named because of a resemblance to bones in the human spinal column.
Vitellaria A type of free-swimming lecithotrophic echinoderm larva. It is barrelshaped, has several transverse rings of locomotory cilia, and lacks a mouth.
Wheels Are common in some apodous holothuroids, they usually have six spokes and a serrated rim.