Phylum Arthropoda

• Class Crustacea (Subclass Ostracoda)
• Class Trilobita

Phylum Brachiopoda

Phylum Bryozoa(Under Construction)

Phylum Echinodermata

• Subphylum Asterozoa
• Subphylum Blastozoa
• Subphylum Crinozoa
• Subphylum Echinozoa
• Subphylum Homalozoa

Phylum Mollusca

• Class Bivalvia
• Class Cephalopoda (Subclass Nautiloidea)
• Class Gastropoda
• Class Monoplacophora

Misc. Groups

• Conchopeltis
• Conularida
• Graptolithina
• Machaeridia

- 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 incude 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.

- 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 occurence 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.

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- 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.

- MORPHOLOGY -

Images taken from Keen, 1969 and Cox, 1969

The images below display basic features of bivalve morphology, including internal and external characteristics.

- TERMINOLOGY -

Definitions of terms taken from Cox, 1969

• Adductor muscle – Muscle, commonly one of 2, connecting 2 valves of shell, tending to draw them together.
• Anisomyarian musculature – With one adductor muscle (anterior) much reduced or absent.
• Auricle – Earlike extension of dorsal region of shell, commonly separated from body of shell by notch or sinus.
• Auriculate – With auricles.
• Beak – Noselike angle, located along or above hinge margin, marking point where growth of shell started.
• Byssal notch – Indentation below anterior auricle of right valve in many Pectinacea (scallops) for passage of byssus (a bundle of hairlike strands used for attachment) or protrusion of foot (a muscular structure for burrowing and locomotion).
• Byssally attached – Temporary attachment made by bivalves to extraneous objects by means of a bundle of hairlike strands.
• Carina – Prominent keel-like ridge.
• Cardinal area – Flat or slightly concave, commonly triangular surface extending between beak and hinge margin in many bivalves, and partly or wholly occupied by ligament.
• Cardinal teeth – Hinge teeth situated close to the beak.
• Concentric – With direction coinciding with that of growth lines. (By no means concentric in literal and geometrical sense of term).
• Costellae – Rather narrow linear elevations of the surface of shell.
• Duplivincular ligament – Type of ligament with lamellar component repeated as series of bands, each with its 2 edges inserted in narrow grooves in cardinal areas of respective valves.
• Equilateral - With parts of shell anterior and posterior to beaks equal in length or almost so.
• Equivalved – With 2 valves of same shape and size.
• Gape – Localized opening remaining between margins of shell when valves are drawn together by adductor muscles.
• Growth line – Line on the surface of shell, one of usually irregularly arranged series, marking position of margin at some stage in growth.
• Hinge – Collective term for structures of dorsal region which function during opening and closing of valves.
• Hinge tooth - Shelly structure (usually one of a series) adjacent to dorsal margin and recieved in socket in opposit valve; hinge teeth serve to hold valves in position when closed.
• Inequilateral – With parts of shell anterior and posterior to beaks differing appreciably in length.
• Ligament – Horny elastic structure or structures joining 2 valves of shell dorsally and acting as spring causing them to open when adductor muscles relax.
• Lunule – Depression, commonly cordate in shape, present anterior to beaks in many bivalves.
• Mantle – Integment that surrounds vital organs of mollusk and secretes shell.
• Modioliform – Shaped like shell of Modiolus; differing from mytiliform in that beaks are not quite terminal and anteroventral region forms slight bulge.
• Muscle scar – Impression on anterior of shell marking former place of attachment of a muscle.
• Opisthocline – Sloping (from lower end) in posterior direction (term applied to hinge teeth and, in some genera, to body of shell).
• Opisthogyrate – Curved so that beaks point in posterior direction.
• Pallial line - Line or narrow band on interior of valve close to margin, marking the line of attachement of marginal muscles of the mantle (integment that surrounds vital organs).
• Pallial sinus – Line or narrow band on interior of valve close to margin, marking line of attachment of marginal muscle of mantle.
• Posterior lateral tooth - Lateral tooth situated posteriorly to beaks and (in heterodonts which have distinctly differentiated cardinal and lateral teeth) posteriorly to ligament.
• Prosogyrate – Curved so that beaks point in anterior direction.
• Radial – Direction of growth outward from beak at any point on surface of shell, commonly indicated by direction of costa (a broad prominent elevation) or other element of ornament.
• Resilifer – Recess or process for attachment of internal ligament.
• Siphonate – Having a siphon (a tubelike extension of mantle for passage of inhalant or exhalent current).
• Socket – Recess for reception of hinge tooth of opposite valve.
• Solemyiform – Recess for reception of hinge tooth of opposite valve.
• Sulcus – Lateral depression of the surface of shell.
• Truncate – With curvature of outline interrupted by straight cut.
• Valve – One of the calcareous structures (2 in most bivalves) of which shell consists.

- MORPHOLOGY -

Images taken from Teichert, 1964

The labeled images below display some morphological attributes of cephalopods, specifically of the nautiloids.

- TERMINOLOGY -

Definitions of terms taken from Teichert, 1964

• Actinosiphonate – Descriptive of endosiphuncular deposits consisting of radially arranged longitudinal lamellae.
• Annulation – Ringlike expansion of conch, either transverse or slightly oblique to longitudinal axis of conch.
• Annulosiphonate deposits – Descriptive of endosiphuncular deposits having shape of rings formed at septal foramen and attached to inside of septal neck.
• Aperture – Opening of shell through which head-foot protrudes.
• Body chamber – Large undivided, anterior space in conch at open aperture, occupied by animal’s body.
• Brevicone – Short rapidly expanding conch.
• Camera (pl., camerae) – Space enclosed between two adjacent septa but not including siphuncle.
• Cameral deposits – Calcareous deposits secreted against original walls of camerae during life of animal.
• Ciruculus – Cameral deposit on concave surface of cyrtochoanitic septal neck.
• Conch – All hard calcareous parts secreted by nautiloid animal including external shell, septa, and siphuncle, but not cameral deposits and any structures within the siphuncle (syn., test).
• Conchal furrow – Shallow groove on inside of conch wall, located mid-ventrally.
• Connecting rings – Partly calcareous, partly conchiolinous, tubular membrane, that connects septal neck of ellipochoanitic (having relatively short retrochoanitic septal necks which do not reach as far as preceeding septum) conchs with septum immediately behind it; vestiges of it are also found in holochoanitic forms.
• Cyrtochoanitic – Descriptive of comparatively short, retrochoanitic septal necks which are curved so as to be concave outward.
• Cyrtocone – Curved conch that completes less than one whorl.
• Dorsomyarian – Descriptive term applied to nautiloids in which retractor muscles of head-foot are attached to shell along interior areas of body chamber adjacent to, or coincident with, its dorsal mid-line.
• Dorsum – Side of animal or conch opposite venter. Among fossil nautiloids, if position of hyponomic sinus (and therefore venter) cannot be established, the term is loosely applied (1) in coiled forms to the concave side of a whorl, (2) in straight or curved conchs with eccentric siphuncle to the side farthest removed from the siphuncle.
• Endocone– One of series of calcareous cones formed in the posterior or adapical portion of siphuncle mainly of endocerid and discosorid conchs.
• Endosiphuncle – Space within ectosiphuncle (walls of the siphuncle) including all organic tissues and calcareous structures.
• Endosiphuncular tube – (1) Circular tube formed by adapical thickening of lateral walls of endosiphocoleon (flattened tube or balde surrounding endosiphuncluar tube) in some Encocerida; (2) simple tubes connecting apices of endocones where no differentiation coleon and tube is possible.
• Episeptal deposits – Cameral deposits on concave (or adapertural) side of septum.
• Exogastric – Descriptive of conchs curved or coiled so that venter is on or near outer convex side.
• Gibbous - A prominent swelling to one side.
• Growth lines – Markings on surface of conch that denote periodic increases in size and hence former positions of aperture.
• Gyroconic – Loosley coiled conch in successive whorls are not in contact with each other.
• Holochoanitic – Descriptive of retrochoanitic septal necks that extend backward through length of one camera.
• Hyposeptal deposits – Cameral deposits on convex (adapical) side of septum.
• Hyponomic sinus – Large concave sinus in middle of aperture, marking location of hyponome, invariably ventral.
• Lirae – Parallel fine ridges or raised lines on surface of conch, transverse or longitudinal, separated by striae. [Restricted to features not easily discernible to the naked eye.]
• Mural deposit – Cameral deposits along mural parts of septa (the parts of the septum attached to wall of conch).
• Nummuloidal – Having siphuncular segments that are strongly inflated between septa, mostly in Actinocerida.
• Orthocone – Straight conch.
• Othochoanitic - Descriptive of retrochoanitic septal necks which are straight, cylindrical, and extend only a short way to preceeding septum.
• Phragmocone – Chambered portion of conch.
• Retrochoanitic – Descriptive of septal necks which are directed backward.
• Septal foramen – Opening in septum allowing passage of siphuncular cord.
• Septal neck – Portion of septum which is bent adapically (or backward) around septal foramen.
• Septum – Partitions dividing phragmocone into camerae and attached to inside of wall of conch.
• Sinus – Any part of transverse feature (apertural margin, ribs, growth-lines) concave toward aperture.
• Siphuncle – Long slender or thick tube extending through all camerae to apex and consisting of soft and shelly parts, including septal necks, connecting rings, calcareous deposits, and siphuncular cord (adj., siphuncular).
• Siphuncular - See siphuncle.
• Striae – Parallel, small to minute grooves or channels on surface of conch, either transverse or longitudinal, separated by lirae. [Restricted to features not easily discernible to the naked eye.]
• Suborthochoanitic – Descriptive of retrochoanitic septal necks that are short and straight, with slightly outwardly inclined tips but with no measurable brim.
• Suture – Line of junction of free part of septum and inner side of phragmocone wall.
• Test – See conch.
• Torticone – Conch coiled in helicoidal spire, as in gastropods.
• Venter – Underside of organism and of conch, distinguished generally by hyponomic sinus and often by conchal furrow.
• Whorl – Complete turn of coiled conch (syn., volution).
  

- MORPHOLOGY -

Image modified from Moore and Harrington, 1967

The image below shows the external characteristics of conularids.

- MORPHOLOGY -

Images from Berry in Boardman, Cheetham, and Rowell, 1987

The images below show examples of the principle soft part anatomy of graptolites and the hard exterior morphology (which is commonly preserved).

- MORPHOLOGY -

Images from Adrain, 1992

The sketch below illustrates two different kinds of Machaeridian body plans.

© 2004 President and Fellows of Harvard College