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.

P

PALLETS
PALLETS fig.Calcareous valve-like structures associated with the SIPHONS (Teredinidae) (figure: Bankia carinata).
PALLIAL
Pertaining to the MANTLE (= pallium).
PALLIAL CAVITY
See MANTLE CAVITY.
PALLIAL EYE
See EYE.
PALLIAL GILLS
PALLIAL GILLS fig.A series of ridges, complex folds, or pectinate structures on the inner mantle surface that serve as accessory respiratory organs of Lucinidae, and aid in functionally separating respiratory surfaces from the location of the endosymbionts (figure: Lucinidae).
PALLIAL LINE
PALLIAL LINE fig.Impressed line (continuous or discontinuous) on the interior of the shell, usually paralleling the ventral margin between the anterior and posterior ADDUCTOR MUSCLES, which indicates the attachment of the pallial muscles and can include a pallial sinus; see also ENTIRE, PALLIAL SINUS (figure: Scissula similis).
PALLIAL MUCUS GLANDS
PALLIAL MUCUS GLANDS fig.Glands lining the mantle edge near the pedal gape that produce mucus that assists in the removal of pseudofeces; occurring in such families as Hiatellidae, Myidae, and Corbulidae (figure: Hiatellidae).
PALLIAL ORGAN
PALLIAL ORGAN fig.A posterodorsal muscular stalk-like structure with a conical glandular head that serves to clear the suprabranchial chamber of shell fragments when the exposed edge of the shell is broken and the mantle withdrawn (an alternative defensive function has also been proposed); a SYNAPOMORPHY of Pinnidae; also called dorsal pallial tentacle (figure: Pinnidae).
PALLIAL RIB
See PALLIAL RIDGE.
PALLIAL RIDGE
PALLIAL RIDGE fig.Longitudinal median ridge present internally in most species of the family Malleidae, extending from either the VISCERAL RIM or more dorsally from the insertion of the pallial retractor muscle, probably serving to strengthen the thin-walled, elongated shell; also called pallial rib (figure: Malleus candeanus).
PALLIAL SINUS
PALLIAL SINUS fig.An embayment in the posterior part of the PALLIAL LINE that indicates the attachment of siphonal retractor muscles and demarcates that part of the MANTLE CAVITY into which the SIPHONS can retract; the presence of a sinus in a PALLIAL LINE has been called sinulapalliate (figure: Periglypta listeri).
PALLIAL SIPHON
See INCURRENT SIPHON.
PALLIAL VEIL
PALLIAL VEIL fig.Expanded inner mantle folds that serve to close or partially close an unfused mantle margin when the valves are gaping; occurring in such families as Pteriidae, Isognomonidae, Malleidae, Ostreidae, Gryphaeidae, Pinnidae, Limidae, Pectinidae, Propeamussiidae, Spondylidae, Plicatulidae, Anomiidae; also called velum (figure: Limidae).
PALP CAECUM
See PALP POUCH.
PALP POUCH
PALP POUCH fig.Unpaired concave structure at the posterior end of the LABIAL PALPS of Nuculidae, which receives food particles from the PALP PROBOSCIDES prior to transport to the palps for sorting; also called palp caecum (figure: Nuculidae).
PALP PROBOSCIDES (sing. palp proboscis)
PALP PROBOSCIDES (sing. palp proboscis) fig.Ciliate tentaculate extensions of the posterior ridge of the palp lamellae in Protobranchia, which are used for DEPOSIT FEEDING (figure: Nuculidae).
PALPS
See LABIAL PALPS.
PARALECTOTYPE
See LECTOTYPE.
PARATYPE
One of potentially several specimens examined at the same time as the HOLOTYPE and serving as additional representatives of the species concept (currently usually so designated by the original author in the original description); see also HOLOTYPE, LECTOTYPE, SYNTYPE.
PARIVINCULAR
PARIVINCULAR fig.Type of dorsal LIGAMENT that is OPISTHODETIC in position, cylindrical in shape, and dorsally arched (in the form of a C-spring), consisting of an elongated lamellar layer running along the HINGE, a long submarginal fibrous layer, and in some cases a ventral shelly layer (LITHODESMA), supported by NYMPHS; occurring in such families as Solemyidae, Astartidae, Carditidae, Condylocardiidae, Thraciidae, Lucinidae, Ungulinidae, Thyasiridae, Chamidae, Lasaeidae, Hiatellidae, Gastrochaenidae, Trapezidae, Sportellidae, Corbiculidae, Cardiidae, Veneridae, Tellinidae, Donacidae, Psammobiidae, Semelidae, Solecurtidae, Pharidae, Mactridae, and Dreissenidae; see also LITHODESMA, NYMPH.
PEARL
A calcareous body of variable color (most familiarly white or bluish grey) comprised of concentric layers around a central nucleus, organically produced by a living mollusk (in addition to its normal shell) and highly prized as a gem for its luster; most characteristic of Pteriidae, but also produced by other shelled mollusks (e.g., Veneridae, see p. 00).
PEARL SACK
Mantle epithelium (usually within the gonad) surrounding a developing cultured pearl and that secretes the nacre.
PECTINEUM
See CTENOLIUM.
PECTINIDIUM
See CTENOLIUM.
PECTINIFORM STAGE
Early postlarval stage of Spondylidae, characterized by byssal attachment and prior to cementation.
PEDAL GLAND
A gland in the foot.
PEDAL ORGAN
PEDAL ORGAN fig.A digitiform process on the foot of Gastrochaenidae, that secretes chemicals that assist in boring (figure: Gastrochaenidae).
PEDAL SCAR
Mark on the internal surface of a burrow or IGLOO of Gastrochaenidae, indicating the position of the foot.
PEDIVELIGER
Planktonic larval stage subsequent to the veliger but prior to metamorphosis (settling), at which point the larva has gained use of its foot, and alternates swimming in the water column and crawling on the bottom; see also VELIGER.
PEDOMORPHOSIS
Evolutionary process by which juvenile or even larval traits are retained in adult (reproductively mature) life stages. There are two alternative processes of pedomorphosis: PROGENESIS, or the acceleration of sexual maturity relative to somatic development, and NEOTENY, or retardation of somatic development with respect to the onset of reproduction.
PERICALYMMA
PERICALYMMA fig.Larval type characteristic of Protobranchia, characterized by a ciliated epithelial covering (calymma) of the larva, and which is either discarded or ingested at metamorphosis; see also VELIGER.
PERIOSTRACUM
PERIOSTRACUM fig. no. 1PERIOSTRACUM fig. no. 2Organic "conchiolin" outer layer of the shell, secreted by the MANTLE, present in various forms from varnish-like to shaggy, also called epidermis by earlier authors (figures: Fugleria tenera, Eucrassatella speciosa).
PHOTORECEPTOR
See EYE.
PLANIVINCULAR
PLANIVINCULAR fig.Type of dorsal LIGAMENT that is OPISTHODETIC in position, cylindrical in shape, and dorsally arched (in the form of a C-spring), consisting of an elongated lamellar layer running along the HINGE, a long submarginal fibrous layer, and in some cases an innermost shelly plate (LITHODESMA) [all so far same as PARIVINCULAR] but supported only by PSEUDODONYMPHS; occurring in such families as Mytilidae, Pinnidae, and Poromyidae; see also LITHODESMA, PARIVINCULAR, PSEUDONYMPH.
PLANKTOTROPHIC
Larval development type characterized by a free-swimming stage (VELIGER) that feeds in the plankton.
plate, sieve
See SEPTIBRANCH.
PLEUROTHETIC
Lying or resting on or cemented by one valve (pertaining only to epifaunal species).
PLICATE
See HETERORHABDIC.
PLICATE ORGAN
Vascularized longitudinal series of transverse folds between each inner demibranch and the visceral mass in Mytilidae, which serves as an accessory respiratory organ.
PORCELLANEOUS
Having a glossy appearance, also called non-NACREOUS.
POSTERIOR
Anal end.
POSTRECTAL MUSCLE
POSTRECTAL MUSCLE fig.Small muscle arching between the two valves dorsal to the HINDGUT in Propeamussidae (figure: Propeamussiidae).
PRE-ORAL GLAND
Unpaired excretory gland lying dorsal to the mouth in Pinnidae.
PRISMATIC
Shell microstructural variety consisting of parallel columnar (but not strongly interdigitating) prisms of aragonitic or calcitic calcium carbonate.
PRISMATONACREOUS
With shell microstructure consisting wholly or primarily of prismatic and nacreous layers.
PROBING TUBULES
Small tubes extending from the anterior end of a Gastrochaenidae burrow, possibly constructed to anticipate features of the substratum ahead of the boring process.
PROBOSCIDES (sing. proboscis)
See PALP PROBOSCIDES.
PRODISSOCONCH
PRODISSOCONCH fig.Larval shell, located at the tip of the UMBONES (equivalent to the protoconch in gastropods); in planktonic developing bivalves, two distinct growth phases (PI and PII) are present, separated by a distinct growth line or change of sculpture; in a non-planktonic developing species, no such transition is visible (figure: Cratis antillensis).
PROGENESIS
See PEDOMORPHOSIS.
PROMYAL PASSAGE
PROMYAL PASSAGE fig.Passage either (1) between the posterior ADDUCTOR MUSCLE and visceral mass (in Malleidae) or (2) in front of the posterior adductor muscle, lateral to the visceral mass (right side only in Ostreidae, both sides in Gryphaeidae) (these two conditions probably not homologous), which allows excurrent water to pass posteriorly with greater efficiency (figure: Malleidae).
PROSODETIC
Type of dorsal LIGAMENT that occurs entirely on the anterior side of the UMBONES; see also AMPHIDETIC, OPISTHODETIC.
PROSOGYRATE/PROSOGYROUS
PROSOGYRATE/PROSOGYROUS fig.Having the UMBONES curling anteriorly; see also OPISTHOGYRATE, ORTHOGYRATE (figure: Periglypta listeri).
PROTANDRIC/PROTANDROUS
A form of HERMAPHRODITISM in which the male phase precedes the female phase during the life cycle of the same individual; see also HERMAPHRODITE.
PROTOBRANCH
PROTOBRANCH fig.Gill type characterized by simple broad leaf-like filaments that are unconnected or loosely connected only by CILIATED DISKS on the filament faces, have chitinous supporting rods, and are used primarily for respiration (rather than feeding); this character forms the basis of the group PROTOBRANCHIA, recognized by Pelseneer (1891), Ridewood (1903), and by current classifications.
PROTOGYNOUS
A form of HERMAPHRODITISM in which the female phase precedes the male phase during the life cycle of the same individual; see also HERMAPHRODITE.
PROTOPLAX
PROTOPLAX fig.Accessory shell plate in Pholadidae and Teredinidae anterior to MESOPLAX, both of which protect the anterior ADDUCTOR MUSCLE (figure: Cyrtopleura costata).
PROTOSTYLE
PROTOSTYLE fig.Rod-shaped amorphous inclusion in the TYPE I STOMACH of members of PROTOBRANCHIA that reduces the size of ingested food particles through rotating abrasion against the gastric shield (and chitinous lining if present); produced by secretory tissues in the STYLE SACK and comprised of mucus and ingested food particles; believed homologous with the CRYSTALLINE STYLE of most other mollusks, which also contains the starch-digesting enzyme AMYLASE; see also AMYLASE, CRYSTALLINE STYLE, PROTOBRANCHIA, STOMACH, STYLE SACK.
PROVINCULAR TEETH
Larval or early-stage hinge teeth (the hinge plate is called the provinculum at this stage).
PROXIMAL VALVE
PROXIMAL VALVE fig.Thin tissue flap at the base of a SIPHON that serves to narrow the lumen and thus control water flow into or out of the MANTLE CAVITY; occurring in such families as Mytilidae, Gastrochaenidae, and Veneridae; also called siphonal membrane (figure: Veneridae).
PSEUDOCTENOLIUM
CTENOLIUM-like structure formed from external sculpture on the edge of the right side of the byssal gape in Pectinidae (some) and Propeamussiidae.
PSEUDOFECES
Waste particles in the MANTLE CAVITY that must be ejected; usually some consolidation occurs through secretion of mucus and the action of ciliated tracts on the inner mantle surface; ejection of pseudofeces commonly happens through the INCURRENT APERTURE or SIPHON or through the FOURTH PALLIAL APERTURE (if present) by rapid contraction of the ADDUCTOR MUSCLES.
PSEUDOLAMELLIBRANCH
Gill type characterized by filaments joined by a combination of ciliary and tissue junctions (the latter "occasional" or "few"); occurring in such families as Pteriidae, some Isognomonidae, some Malleidae, Ostreidae, Gryphaeidae, Pinnidae, Pectinidae, Spondylidae, and some Thyasiridae; see also EULAMELLIBRANCH, ELEUTHERORHABDIC, FILIBRANCH.
PSEUDONYMPH
A ridge-like support for a more advanced type of dorsal LIGAMENT that faces the median plane of the shell (is not rotated dorsally; thus not enhancing the dorsal arching of the ligament); see also LIGAMENT, NYMPH.
PYLORIC PROCESS
See METASOMA.