# Phylum Echinodermata ## expand\_more ### Subphylum Asterozoa expand\_more #### MORPHOLOGY Images modified from figure in Spencer and Wright, 1966 Images below compare the morphology between recent asterozoans. ![Recent Asteroid morphology of Anthenea flavescens](/sites/g/files/omnuum8411/files/styles/hwp_1_1__360x360_scale/public/trenton/files/asterozoadiagram.jpg?itok=C-847sat) Recent Asteroid morphology of Anthenea flavescens ![Recent Ophiuroid morphology of Ophiura](/sites/g/files/omnuum8411/files/styles/hwp_1_1__360x360_scale/public/trenton/files/asterozoadiagram2.jpg?itok=Tw4FNRBp) Recent Ophiuroid morphology of Ophiura#### 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. ### Subphylum Blastozoa expand\_more #### 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. ### Subphylum Crinozoa expand\_more #### MORPHOLOGY Image from Ubaghs, 1978 Basic crinoid morphology is labeled on the sketch below. ![Crinoid Morphology based on Calpiocrinus intermedius.](/sites/g/files/omnuum8411/files/styles/hwp_1_1__360x360_scale/public/trenton/files/crinoiddiagram.jpg?itok=E6j-dlX0) [*Crinoid Morphology based on Calpiocrinus intermedius.*](https://static.hwpi.harvard.edu/files/styles/os_files_xlarge/public/trenton/files/crinoiddiagram.jpg?m=1525724707&itok=o2hi4q9d)#### 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. ### Subphylum Echinozoa expand\_more #### MORPHOLOGY Image modified from Regnell, 1966 The following image is provided to simply give an idea of basic external characteristics of Edrioasteriods. ![Edrioasteriod (Echinozoan) morphology based on Edrioaster bigsbyi](/sites/g/files/omnuum8411/files/styles/hwp_1_1__360x360_scale/public/trenton/files/edrioastermorphology.jpg?itok=_zb-N2bH) [*Edrioasteriod (Echinozoan) morphology based on Edrioaster bigsbyi*](https://static.hwpi.harvard.edu/files/styles/os_files_xxlarge/public/trenton/files/edrioastermorphology.jpg?m=1525724957&itok=KuqwB31-) ### Subphylum Homalozoa expand\_more #### MORPHOLOGY Images from Sprinkle and Kier, 1987 The images below illustrate the external characteristics of Stylophora (left thumbnail) and Homoiostele (right thumbnail) Homalozoans. ![Morphology of Stylophora Based on Phyllocystis](/sites/g/files/omnuum8411/files/styles/hwp_1_1__360x360_scale/public/trenton/files/carpoiddiagram.jpg?itok=Kpxq_5FD) Morphology of Stylophora Based on Phyllocystis ![Morphology of Homoiostele Based on Iowacystis (A, upper side, B, lower side, C, section through the theca)](/sites/g/files/omnuum8411/files/styles/hwp_1_1__360x360_scale/public/trenton/files/carpoiddiagram2.jpg?itok=kc4UC20R) Morphology of Homoiostele Based on Iowacystis (A, upper side, B, lower side, C, section through the theca)#### 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.