Pele Cy Pods
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Shell MorphologyMantle - a thin membrane surrounding the body, secretes the shell valves, ligament, and hinge teeth.Shell consists of three distinct layers:Nacre- inner most layer, thin sheets of CaCO3 laid down horizontally (parallel to plane of shell) gives iridescent appearance; how it is laid down determines color; ranges from white to peach to pink to deep purple; Sphaeriids usually lack this layer and in corbiculids it is very thinPrismatic- 90% of shell; also CaCO3 laid down in vertical layers (90o to the horizontal plane)Periostracum- outer proteinaceous, horny layer; thickness varies with species; in unionids it is usually comprised of three layers
Structures on the ShellUmbone (=beak)- area where first shell was laid down in developmentUmbonal cavity (beak cavity)- inside, area under umboneInterdentum- space between teeth types (ie. between lateral and pseudocardinal teeth)Pallial line - muscle scarsLateral teeth - used as a locking mechanism to keep valves from slidingOrientation: Right, Left valves; Dorsal and VentralAnnual growth rings- much like tree rings; laid down as individual grows; have been used to age species
Alae- wing; condition is said to be "alate"Flutings- broad grooves and channels in side of shellsPustules- warts or knobs or tubercles; any bumps on the surface of the shellRays- green colored bands on side of shell; sometimes narrow sometimes broad or may be restricted to certain parts of the shell
Internal MorphologyMantle covers the body and lines the internal layer of the shell;responsible for secreting the shell; folds in the mantle produce siphons: inhalant (located vantrally) and exhalant (dorsal); located on posterior end of bodyGills are very large and paired on both sides of body formed into large lamellae or leaf like structures that almost completely surround bodyare highly vascularizedassociated with dorsal heart that sends blood from the gills to the visceral mass, mantle, foot and backhave multiple functionsRespiration- take up oxygen and give off carbon dioxideFeeding- aid in filter feeding; water brought across the gills which contains food; food is trapped by mucous on gills and is then moved by ciliary system to mouth; this process may produce pseudofecesReproduction- the gills act as a marsupium chamber for developing larvae or young
Visceral Masscontains most of the vital organsstomach and intestinesdigestive gland (i.e., liver)gonads Heartdorsal three chambered; covered by a pericardium; pumps blood (hemolymph) around bodyKidneyFoot largest muscle of body used for locomotion and diggingMusclesAnterior and Posterior Adductor Muscles- close shell; no mechanism except relaxation of these muscles and flexibility of hinge ligament to open shellAnterior and Posterior Retractor muscles- used to retract foot into shell; and in doing so pull the shell forward during locomotionProtractor muscle- opposes action of retractor muscles
Other structuresMorphology of a bivalve differ from one specie to another and this is reflected in their differing: tooth patterns and gill structure
TOOTH TYPEDESCRIPTION DESMODONTTeeth are reduced or absent all togetherDYSODONTSmall simple teeth located near the edge of the valveTAXODONTNumerous teeth arranged in a radial pattern fanning out upwardsACTINODONTNumerous teeth arranged in a radial pattern fanning out downwardsISODONTLarge teeth found either side of the internal ligament pitSCHIZODONTLarge teeth, sometimes groovedPACHYODONTVery large blunt teethHETERODONTCardinal and lateral teeth
GILL TYPEDESCRIPTIONPROTOBRANCHThis gill structure tends to occur in primitive groups, and appears as a small leaf-like structureFILIBRANCHThis gill structure consists of individual filaments forming 'W'-shaped structures that come together to form lamellar sheets.EULAMELLIBRANCHThese form 'W'-shaped gills with cross-partitions joining the filaments to create water-filled cavities in between them.SEPTIBRANCHThese gills are only found in Poromyacea a super-family of the rock borers. They run transversely across the mantle cavity, enclosing the inner chamber, with only a small connection to the outer cavityPelecypodsTaxonomic ClassificationTaxonomyPhylum: MolluscaClass: BivalviaSubclass: ProtobranchiaOrder: NuculoidaOrder: SolemyoidaSubclass: PteromorphiaOrder: MytiloidaOrder: PterioidaSubclass: PalaeoheterodontaOrder: TrigonioidaOrder: UnionoidaSubclass: HeterodontaOrder VeneroidaOrder MyoidaSubclass AnomalodesmataOrder PholadomyoidaSubclass: ProtobranchiaEarly Cambrian to Recentthe simplest and most primitive of the bivalves They have a protobranch gill structure, an equivalved aragonite shell and taxodont dentition.Order Nuculoida shell is aragonic with an interior that is nacreous or porcelaneous periostracum is smooth. valves are equal and have a row of sharp teeth along its hinge or border. Large palps used for food collection. Gills are small and used only for gas exchange. Foot is longitudinally grooved and has a plantar sole. Common Name: Nut Clams
NeilonellidaeSubclass: ProtobranchiaOrder Solemyoida (Devonian to Recent) Shell valves are thin, equal in size, elongate and lacking hinge teeth (dysodont). have a large gills used for both feeding and gas exchange. Their palps are small. Common Name: awning clams
Subclass PteromorphiaA very diverse group of normally byssate forms with variable musculature and dentition. Shells may be calcite, aragonite or both. Many inequivalved, some equivalved. Variable dentition. Foot commonly reduced, absent in some. Mantle mostly unfused and lacking siphons. Gills fillibranch or eulamellibranchOrder Mytiloida Shell valves are quite thin, elongated and equal in size. The valves are uncalcified along the outer edges and hinge teeth are absent.They have one large ctenidia which is used both for feeding and gas exchange.Their palps are small.
Mytilidae: these are the sea musselsOrder Pterioida Ordovician to RecentInclude pectinaceans (scallops and their kin), ostreaceans, and the fossil inoceramids
Pinnidae Subclass PalaeoheterodontaThey are distinguished by having the two halves of the shell be of equal size and shape, but by having the hinge teeth be in a single row, rather than separated into two groupsOrder Trigonioida Bivalves with large trigonal and well developed schizodont teethDevonian to Recent
Yaadia valentinaOrder Unioinoidafreshwater clamsthe only non-marine bivalvesDevonian to Recent
HyriidaeSubclass Heterodonta(Triassic to Recent) Heterodont hinge structure eulamellibranch gill structure almost always aragonitic shells Adapted to varied modes of life, especially infaunal siphon feedingThe hinge structure may degenerate into a desmodont condition.
Order Veneroida mostly active equivalve heterodonts with true heterodont teeth Usually thick-valved, and isomyarian.
Veneroida TellinoideaOrder Myoida Thin-shelled burrowers and borers very inequivalve hinges are degenerate, with one cardinal tooth on each valve; siphons well developed Carboniferous to Recent
Pholadidae Subclass AnomalodesmataMiddle Ordovician to Recent Burrowing or boring forms very modified, with aragonitic shells and desmodont dentition. A small, specialized group, in whichgills are not present. The inhalent and suprabranchial (exhalent) cavity are separated by a pumpingseptumOrder Pholadomyoida The shells of species in this order are of equal size, as are the muscles that hold them closed the margins at the hinges are thickened. The margins of the mantle are also fused, and there is only a single hinge tooth, if any