Phylum Echinodermata

MORPHOLOGY

Images modified from figure in Spencer and Wright, 1966

Images below compare the morphology between recent asterozoans.

TERMINOLOGY

Definitions of terms taken from Spencer and Wright, 1966

Adambulacral  Ossicle of series on oral surface of ray, next to ambulacrals.
Ambulacral  Ossicle of axial skeleton, one of double series of opposite or alternate ossicles formed along radial water vessel that constitutes axis of ray or arm; also pertaining to series of ambulacral ossicles.
Ambulacral groove  Axial depression along oral surface of ray that is roofed by series of ambulacral ossicles.
Ampulla (pl., ampullae)  Dorsal saclike part of tube foot, either seated externally in cupule or internally and connecting with podium (external extension of tube foot) through podial opening; ampullae may be single or double.
Arm  Radial extension of the body surrounding axis consisting of ambulacra (ossicle of axial skeleton); arms may be distinct from disk or not.
Axillary  In axil (an angle formed by junction of rays or arms with straight sides); generally applied to single large ossicle in axils of certain asteroids.
Carinal  Ossicle of a series along mid-line of aboral surface of ray, in line with primary radial if present.
Disk  Central part of body, more or less distinctly separable from arms.
Dorsolateral  Ossicle of series on aboral surface of ray, between carinals and marginals (syn., adradial); also directed toward axis of ray.
Granulate  Covered with granules. Granules are minute, more or less spherical skeletal elements situated on the surface of ossicles, generally in pits or distributed in covering skin.
Inferomarginal  Ossicle of a series along the oral edge of arms or disk or both; in origin part of the adaxial skeleton.
Interbrachial  Between the arms; applied to margin or surface of disk or to internal structures.
Interradial  Indicating position midway between axis of adjacent rays or area between such rays.
Madreporite  Spongy or sievelike ossicle that serves as inlet to the water vascular system; it is located interradially, lateral in some primitive asterozoans, but on the aboral surface in most asteroids and a few ophiuroids and on the oral surface in other phiuroids.
Marginal  Ossicle of a series along the edge of the body.
Ossicle Any individual calcified element of skeleton, but normally used for larger of such elements.
Papula (pl., papulae)  Short protuberance of integment between ossicles of aboral or oral surface of asteroids that functions as external gill.
Papular opening  Gap between ossicles for protrusion of papula.
Paxilla (pl., paxillae)  Ossicle of extraxial skeleton with shaft surmounted by tuft of spinelets.
Peristomal ring Plates surrounding the opening for mouth.
Podial opening  Passage between ambulacrals for passage of tube foot.
Radial  Prominent ossicle on aboral surface of asteroids, in line with mid-line of arm, forming part of primary circlet; commonly used in older literature for any ossicle in series with primary radial (see carinal); also applied to organs extending along arms.
Ray Segment of the body that includes one ambulacral axis.
Spine  Sharp or blunt, short or long skeletal element, attached to ossicle by muscle.
Superomarginal  Ossicle of series along edge of disk or arms or both, above series of inferomarginals. 

TERMINOLOGY

Definitions of terms taken from Kelsing, 1967

Ambulacral groove  Groove through which food was conveyed from brachioles to mouth, covered by ambulacral covering plates; in some cystoids lying within flooring plates as zigzag trough, but in others lying directly in surface layer of thecal plates or concealed by a tegmen (structure which covers mouth and ambulacral groove).
Ambulacrum  Structure in which food was conveyed from brachioles to mouth, always on surface of theca, never erect, exothecal. Five ambulacra in many cystoids, but number may be reduced to 2. Length of ambulacra varies greatly, from very short conduits, where brachioles are clustered near the mouth, to medium, where brachioles are limited to crown of theca, to very long, in some extending to base. Each ambulacrum consisting of ambulacral groove enclosed by biserial covering plates; some ambulacra provided with flooring plates, others with groove entrenched into thecal surface.
Arm  Major element in food-gathering structure in some cystoids. Has biserially arranged plates bearing biserial pinnules.
Base  Aboral part of theca, by some restricted to columnar facet (face on columnals allowing movement) but by others expanded to include thecal plates and basal circlet or aboral circlets.
Brachioles  One of erect structures by which food is gathered and transmitted to ambulacrum. Each brachiole composed of biserial plates and unbranched. Two rows of dorsal plates include brachiole groove, and 2 rows of tiny ventral plates roof it over.
Calyx (pl., calyces)  Part of theca excluding tegmen (structure which covers mouth and ambulacral groove).
Column  Stemlike structure attached to aboral end of most cystoids, fairly rigid in Caryocrinites but in most other forms having proximal section flared and flexible. Column presumably used for anchoring cystoid, distal end known to be variously modified in some species.
Columnal  Unit of ossicle composing column. Columnals in many species varying according to position in column, distal columnals longer, cylindrical, with narrow central canal, and proximal columnals shorter, ringlike, with wide lumen. Certain proximals strongly modified in some cystoids.
Crenulate  Minutely scalloped.
Food grooves  See ambulacral groove.
Holdfast  Distal structure of column that helps to anchor creature in place.
Nodose  Having a nodular appearance.
Ossicle  Any calcified piece of exoskeleton.
Pectinirhombs  Type of pore rhomb (group of perforations in thecal plates) found in Glyptocystitida, with units or dichophores terminating in perforations through thecal plates, either as round pores or, more commonly, as slits. If slits from one plate are continuous with those of another, pectinirhomb is conjunct; if slits from one plate are separated from those of other by slit free area, pectinirhomb is disjunct; if each dichophore has line of slits in each plate, instead of terminal slit only, pectinirhomb is multidisjunct; and if slits in one half-rhomb are surrounded by rim, pectinirhomb is montidisjunct.
Periproct  Major thecal tract containing anal pyramid and, in many species, additional plates; extreme development attained in Pleurocystitidae, in which periproct nearly fills one side of compressed theca. In many Callocystitidae, periproct is filled by small anal pyramid and surrounding ring of auxiliary plates.
Pinnule  Branch of the food gathering system of armed cystoids, it differs from pinnules of crinoids in that it is biserial. It is homologous to simple brachioles in other cystoids.
Plate  Any calcareous ossicle, normally flat, in cystoid; by some used only for thecal plates, but all calcareous bodies formed serve as framework of support for soft parts and constitute plates.
Ray  See ambulacrum.
Stem  See column.
Suture  Area of contact between two plates.
Theca  Enclosure of plates in which body of cystoid was housed.

MORPHOLOGY

Image from Ubaghs, 1978

Basic crinoid morphology is labeled on the sketch below.

 TERMINOLOGY 

Definitions of terms taken from Moore et al., 1978

A ray  Anterior ray located opposite the posterior interray designated CD, generally wider than others and containing anus or anal plates; includes radial and succeeding brachitaxes with intervening plates as well as pinnules. Other rays designated B, C, D, and E in clockwise order from A, viewing adoral side of theca.
Aboral cup  Part of aboral side of body between origins of free arms and column.
Anal sac  Variously shaped, generally inflated and strongly elevated part of tegmen as developed among inadunate crinoids.
Anal tube  Conical to cylindrical structure, usually of considerable height, bearing anal opening at its summit, typically developed in many camerate, flexible, and articulate crinoids.
Arm  Radial evagination of body above radial, normally extending upward or outward from theca, containing coelomic canals, and composed of pinnulate or nonpinnulate brachitaxes. Restricted by some authors to undivided distal branches.
Axial canal  Longitudinal passageway for axial cord penetrating columnals, cirrals, thecal plates, arms, and pinnules, generally but not invariably located centrally; may be simple or multiple with main canal accompanied by smaller accessory ones.
Axillary  Brachials (any plate above the radials or biradials) that support two arm branches.
Axil-arm  Arm including its branches borne by any branch of main-axil as seen in calceocrinids but excluding terminal branchlet termed omega-ramule.
Basal  Any plate of circlet next proximal to radials, each basal typically in interradial position.
Bilateral heterotomy  Type of arm branching characterized by occurrence of ramuli on either side of main arm.
Brachitaxis  Series of brachials (any plate above the radials or biradials) extending from radial or biradial to and including primaxil or in arms lacking axillaries to distal extremity of arm; likewise brach series extending from any axiallary to and including next one or to distal extremity of arm or branch.
Column  Series of segments composing stem; excludes holdfasts.
Columnals  Individual ossicle (calcified segment of skeleton) of crinoid stem.
Crown  Whole crinoid exclusive of stem.
Cup  See aboral cup.
D ray  See A ray.
E ray  See A ray.
Food grooves  Simple or branched furrow running in adoral surface of tegmen, arms, and pinnules; serves to convey food to the mouth.
Heterotomous branching  Arm characterized by division into unequal branches.
Holdfast  Any structure at distal extremity of column serving for fixation.
Infrabasals  Any plate of proximal circlet in aboral cup having two circlets of plates below radials.
Isotomous branching  Characterized by division of arm in equal branches.
Nodose  Having a nodular appearance.
Non-pinnulate  Without pinnules.
Pinnulate  Having pinnules.
Pinnules  Generally slender, unbifurcated, uniserial branchlet of arm, typically borne on alternate sides of successive brachials (any plate above the radials or biradials) except hypozygals and axillaries.
Plate  Tabular ossicle (calcified segment of skeleton), mostly having articular facets at edges.
Primiaxillary  Axillary plate of proximal brachitaxis.
Primibrachs  Plates of proximal brachitaxis; may axillary or non-axillary and fixed or free.
Quartibrachs  Any ray plates of fourth brachitaxis.
Radial  Undivided proximal plate or any ray, may be simple or compound and bearing proximal anal plate.
Ramule  Bifurcating or nonbifurcating minor branch of arms, differing from pinnule in less regular occurrence and in some crinoids by presence of pinnules on it.
Ray  Radial plate, together with all the structures borne by it.
Secundibrachs  Any ray plates of second brachitaxis.
Stem  Stalklike attachment of many crinoids; column.
Tegmen  Adoral part of theca above origin of free arms or occupying space between them; may be calcified or not; may bear anal vent, pyramid, sac, or tube.
Tertibrachs  Any ray plates of third brachitaxis.
Theca  Crinoid skeleton exclusive of pelma (column and holdfast) and free arms.

MORPHOLOGY

Image modified from Regnell, 1966

The following image is provided to simply give an idea of basic external characteristics of Edrioasteriods.

MORPHOLOGY

Images from Sprinkle and Kier, 1987

The images below illustrate the external characteristics of Stylophora (left thumbnail) and Homoiostele (right thumbnail) Homalozoans.

TERMINOLOGY

Definitions of terms taken from Ubaghs, 1967

Stylophora

Placocystitid plate  Special supracentral located on mid-line of theca and generally surrounded by its two neighbors, distinguished by its smooth surface and its rounded (rather than polygonal) outline.
Carapace  Upper face of theca.
Aulacophores  Single jointed exothecal appendage, here interpreted as brachial process carrying ambulacrum (structure in which food is conveyed to the mouth).
Theca  Body skeleton exclusive of aulacophore.

Homoiostelea

Stele  Relatively slender and tapering peduncular prolongation of the body.
Theca  Body skeleton exclusive of stele.