Glossary

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The glossary provided here is largely based on “Seashells of Southern Florida: Bivalves,” by Paula M. Mikkelsen & Rüdiger Bieler, Princeton University Press. Production of this glossary was funded in part by the National Science Foundation’s Partnerships in Enhancing Expertise in Taxonomy [PEET] Program, NSF-DEB-9978119, “Bivalves - Research, Training, Electronic Dissemination of Data” (1999-2008) to Bieler and Mikkelsen.

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ABDOMINAL SENSE ORGANS
ABDOMINAL SENSE ORGANS fig.Small paired swellings near the anus, on the ventral surface of the adductor muscle and receiving innervation from the visceral ganglion, of unknown function but showing characteristics of both chemo- and mechanoreceptors (perhaps related to, as proposed, detection of vibrations or of excurrent water flow); known as a SYNAPOMORPHY of Pteriomorphia (also present in members of Trigoniidae), and occurring in such families as arcoids (Arcidae, Noetiidae, Glycymerididae, Limopsidae), mytiloids (Mytilidae), pterioids (Pteriidae, Isognomonidae, Malleidae, Ostreidae, Gryphaeidae, Pinnidae), limoids (Limidae), pectinoids (Pectinidae, Propeamussiidae, Spondylidae, Plicatulidae, Anomiidae); also known as pallial organ (Ostreidae) (figure: Pteriidae).
ACCESSORY FOOT
ACCESSORY FOOT fig.An elongated process on the FOOT of Malleidae, used to clean the INFRABRANCHIAL CHAMBER (figure: Malleidae).
ACCESSORY GENITAL ORGAN
Pendulous glandular organ on the posteroventral surface of the posterior adductor muscle in male Pholadidae; secretions from this organ are added to sperm before storage in the SEMINAL VESICLE.
ACCESSORY HEART
Enlarged blood vessels in the MANTLE lobes of the SUPRABRANCHIAL CHAMBER that pulsate and deliver blood to the auricles (in Ostreidae).
ACCESSORY PLATE
Secondary calcareous or chitinous structure found in Pholadidae to protect the soft body or serve as an attachment for internal muscles; see also APOPHYSIS, CALLUM, HYPOPLAX, MESOPLAX, METAPLAX, PROTOPLAX, SIPHONOPLAX.
ADDUCTOR MUSCLE
ADDUCTOR MUSCLE fig.One of usually two large muscles (one anterior, one posterior) that contract to close the shell and maintain it in that condition; the position of these muscles is usually clearly marked on the shell interior as an adductor muscle scar or impression (figure: Mercenaria mercenaria).
ADVENTITIOUS
Of or belonging to a structure formed in an unusual place; applied in bivalve biology to the shell igloos or tubes of Gastrochaenidae (Eufistulina) and Teredinidae (Kuphus) that are formed in soft sediment.
ALIVINCULAR
ALIVINCULAR  fig.Type of dorsal LIGAMENT which is usually AMPHIDETIC in position (typically trigonal in shape), with a central fibrous portion (RESILIUM) bordered by anterior and posterior lamellar layers, and occurring in such families as Limopsidae, Philobryidae, some Mytilidae, Pteriidae, Malleidae, Ostreidae, Gryphaeidae, Limidae, Pectinidae, Propeamussiidae, Spondylidae, Plicatulidae, Anomiidae, and Crassatellidae.
AMPHIDETIC
AMPHIDETIC fig.Type of dorsal LIGAMENT that occurs both on the anterior and posterior sides of the UMBONES; see also PROSODETIC, OPISTHODETIC (figure: Tucetona pectinata).
AMYLASE
Starch-digesting enzyme found in the CRYSTALLINE STYLE of most mollusks, including many bivalves.
ANAL APERTURE or SIPHON
See EXCURRENT APERTURE OR SIPHON.
ANAL CANAL
ANAL CANAL fig.Long, narrow, dorsal channel in Teredinidae, which terminates in a sphincter muscle in some species, into which the rectum empties and that is continuous with the SUPRABRANCHIAL CHAMBER and EXCURRENT SIPHON (figure: Teredinidae).
ANAL FLAP
See ANAL FUNNEL.
ANAL FUNNEL
ANAL FUNNEL fig. no. 1ANAL FUNNEL fig. no. 2Ear-like membranous structure protruding from the tip of the rectum at about a right angle to the surface of the posterior adductor and enclosing the anal opening at its base; occurring in such families as Arcidae, Pteriidae, Isognomonidae, Malleidae, some Ostreidae, and Pinnidae; also called anal papilla or anal flap (figure: Pteriidae, Pinctada imbricata).
ANAL PAPILLA
See ANAL FUNNEL.
ANAL TENTACLES
Enlarged pallial tentacles on the posterodorsal margin of some Limidae.
ANISOMYARIAN
See HETEROMYARIAN.
ANTERIOR
Head end.
AORTIC BULB
AORTIC BULB fig. no. 1AORTIC BULB fig. no. 2A muscular, spongy, pendulous structure on the ventral side of the posterior aorta and hindgut just posterior to the heart (anterior to the posterior adductor muscle), which serves to prevent rupture of the heart when the SIPHONS and foot retract suddenly, forcing haemolymph backward into the posterior aorta; occurring in such families as Gastrochaenidae, some Cardiidae, Veneridae, some Tellinidae, Psammobiidae, some Semelidae, some Solecurtidae, Pharidae, and Mactridae (figures: Veneridae, Mercenaria mercenaria).
APERTURE
An opening.
APOPHYSIS (pl. APOPHYSES)
APOPHYSIS (pl. APOPHYSES) fig.Shelly structure to which pedal retractor muscles attach (more generally called MYOPHORE); extending interiorly below the UMBONES and occurring in such families as Teredinidae, Pholadidae, and Dreissenidae (figure: Cyrtopleura costata).
ARAGONITE (adj. ARAGONITIC)
A form of calcium carbonate found in molluscan shells and other hard parts; see also CALCITE, which differs from aragonite in certain characters of crystallization and density.
ARTICULATED
With both valves joined together in living position.
AURICLE
AURICLE fig.(1) ear-like extension of the dorsal HINGE line (see figure), usually present both anterior and posterior of the UMBO, most characteristic of the family Pectinidae, also occurring in such families as Limidae, Malleidae, Propeamussiidae, Pteriidae, some Arcidae, some Philobryidae, and some Plicatulidae; (2) ear-like extension of the posterior shell margin in Teredinidae; (3) chamber of the heart, usually paired in bivalves (figure: Nodipecten fragosus).