Amphioplus thrombodes H. L. Clark, 1918
Family: Amphiuridae
Common names: Brittlestar
Amphioplus thrombodes image
Amphioplus thrombodes  

Species Description: Amphioplus thrombodes is one of several small brittle stars occurring in the Indian River Lagoon. The bumps on the edge of the dorsal scales give the disk a rough, papillate texture (Thomas 1962, Hendler et al. 1995). The five arms have three spines each. The middle spine is thickest and slightly compressed. The disk is pale gray and speckled with brownish scales. The radial shields are joined distally, are tipped in white, and are twice as long as they are wide (Thomas 1962). The arms are pale tan and blotched with dark gray (Hendler et al. 1995).

Potentially Misidentified Species: A. thrombodes resembles A. sepultus, except for the presence of bumps on the edge of the dorsal scales in the former species (Hendler et al. 1995). A. thrombodes also exhibits only a single pair of tentacle scales on most arm joints, and a narrower tip on the middle arm spine.

IRL Distribution: This brittle star is found from Fort Pierce to the southern tip of the IRL.

Size: The disk diameter of A. thrombodes is approximately 5 mm, with arms 60 mm long (Hendler et al. 1995).

Abundance: The sex ratio in populations of A. thrombodes at Cedar Key, Florida has been documented as 1 male to every 0.79 females (Stancyk 1970).

Associated Species: A. thrombodes has been collected with other burrowing brittle stars such as A. sepultus (Hendler et al. 1995).

Hendler G, Miller JE, Pawson DL & PM Kier. 1995. Sea stars, sea urchins, and allies: echinoderms of Florida and the Caribbean. Smithsonian Institution Press. Washington, D.C. 390 pp.

Stancyk SE. 1970. Studies on the biology and ecology of ophiuroids at Cedar Key, Florida. Unpublished MS thesis. University of Florida, Gainesville.

Thomas LP. 1962. The shallow water amphiurid brittle stars (Echinodermata, Ophiuroidea) of Florida. Bull. Mar. Sci. Gulf Carib. 12: 623-694.

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.