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.

S

SCISSULATE
Having sculpture running obliquely across the shell, i.e., not COMMARGINAL or RADIAL.
SCULPTURE
Ornament or markings on the surface (usually of a shell) resembling that produced by a carving tool, see also COMMARGINAL, GROOVE, RADIAL, RIB, STRIA.
SEMINAL VESICLE
Sperm-storage organ, for example in Pholadidae; also called vesicula seminalis.
SEPTAL VALVULA (pl. VALVULAE)
Thick, muscular, dish- or crescent-shaped posterior extensions of the SEPTUM in Poromyidae; also called compensation sack.
SEPTIBRANCH
SEPTIBRANCH fig.Gill type characterized by a laterally suspended muscular pumping SEPTUM pierced by window-like OSTIA containing EULAMELLIBRANCH filaments (BRANCHIAL SIEVES in Poromyidae; also called SIEVE PLATES or OSCULA) or their cilia alone (pores in Cuspidariidae); innervation patterns suggest that the septum is mostly ctenidial in origin; occurring in such families as the heteroconchian heterodont anomalodesmatan Poromyoidea (Poromyidae) and Cuspidarioidea (Cuspidariidae), and functioning solely in respiration; see also SYNAPTORHABDIC. The gills of Verticordiidae are considered "septibranch" by most authors although the gills themselves are separate from the septal ostia, which are perforations in the membrane.
SEPTUM
SEPTUM fig. no. 1SEPTUM fig. no. 2An anatomical partition, either (1) of tissue that separates or assists the gills in separating INFRABRANCHIAL and SUPRABRANCHIAL (or -SEPTAL) CHAMBERS (i.e., body chambers below and above the gills or branchial septum, respectively; figure: Poromyidae), (2) of shell to which pedal retractor muscles attach (see also MYOPHORE; figure: Mytilopsis sallei), or (3) of shell separating the shell and siphonal chambers of a burrow or IGLOO of Gastrochaenidae.
SHIELD
See UMBONAL REFLECTION.
SIEVE PLATE
See SEPTIBRANCH.
SIMPLE LIGAMENT
Type of dorsal LIGAMENT, which is arched or planar, external or submarginal, and set on GUTTERS or FOSSETTES; occurring in such families as Nuculidae, Nuculanidae, Manzanellidae, Yoldiidae, some Arcidae, and some Limopsidae; see also GUTTER, FOSSETTE.
SIMPLE PALLIAL LINE
See ENTIRE.
SINUATE
Of a PALLIAL LINE when a SINUS is present.
SINULAPALLIATE
See PALLIAL SINUS.
SINUS
See PALLIAL SINUS.
SIPHONAL SEPTUM
SIPHONAL SEPTUM fig.Membrane at the base of the INCURRENT/EXCURRENT SIPHONS/APERTURES separating the INFRABRANCHIAL CHAMBER from the SUPRABRANCHIAL CHAMBER; also called branchial membrane/septum (figure: Pandoridae).
SIPHONAL TUBE
Tube composed of feces and/or pseudofecal particles cemented with mucus, which is fused to the SIPHONOPLAX in Pholadidae.
SIPHONOPLAX
SIPHONOPLAX fig.Accessory shell plate in Pholadidae and Teredinidae protecting the SIPHONS (figure: Martesia striata).
SIPHONS
SIPHONS fig.Posterior extensions (usually two) of the MANTLE, made tubular by either tissue fusion or (less often) ciliary junctions of the mantle folds, through which water is directed in and out of the body, along with waste products and gametes (figure: Mercenaria mercenaria). When the siphons are formed by permanent tissue junctions, a classification proposed by Yonge (1957) is often used to reflect the mantle folds involved in their formation:
  • TYPE A: fusion of inner folds only (e.g., Tellinidae)
  • TYPE B: fusion of inner and middle (inner surface only or entire) folds (e.g., Veneridae)
  • TYPE C: fusion of inner, middle, and outer folds (e.g., Myidae); siphons of this type are at least partly encased in periostracum
SMOOTH
See HOMORHABDIC.
STATOCONIA
Multiple small bodies within a STATOCYST; also called otoconia; see STATOCYST.
STATOCYST
Fluid-filled capsule-like sense organ, open or closed, usually paired, and located near the pedal ganglia (ventral to the posterior adductor muscle) but innervated by the cerebral ganglia, and usually including ciliated "hair" cells and containing a single dense body (STATOLITH) or a number of smaller ones (STATOCONIA); the statolith and/or statoconia interact with the cilia lining the capsule, probably (as has been shown in gastropods and cephalopods) conveying information about orientation to the organism; in INEQUIVALVE bivalves (e.g., Pecten) the statocysts are also unequal, with one more complex or larger than the other; usually present in larval bivalves, but often absent in adults; also called otocyst; see also STATOLITH. Morton (1985) defined several types of statocysts in Anomalodesmata (bivalves in other suprafamilial groups have not been so categorized):
  • TYPE A: capsule penetrated by nerve endings and containing a multicellular statolith.
  • TYPE B1: capsule with ciliated cells as sensory receptors, and containing a single large statolith; occurring in such families as Pandoridae, Lyonsiidae, Thraciidae, some Verticordiidae, and Poromyidae.
  • TYPE B2: capsule with ciliated cells as sensory receptors, and containing both a single large statolith and statoconia; occurring in such families as Periplomatidae and some Verticordiidae.
  • TYPE B3: capsule with ciliated cells as sensory receptors, and containing numerous crystal-like statoconia, one of which can be enlarged into a statolith; occurring in such families as some Verticordiidae.
  • TYPE C: small capsule comprised on few cells lined by microvilli, and containing a large oval statolith which does not move freely within the capsule; occurring in such families as Cuspidariidae.
STATOLITH
Single large body within a STATOCYST; also called otolith; see STATOCYST.
STEMPELL'S ORGAN
Specialized mechanoreceptor in Nuculidae on the anterior ADDUCTOR MUSCLE that detects its level of contraction.
STOMACH
STOMACH fig.Major organ for processing food in bivalves, embedded within in the visceral mass, connecting the esophagus and MIDGUT, and featuring ciliated sorting areas, grooves, and other surfaces, openings to ducts to the digestive diverticula, and in most cases a rotating rod-like structure (see also CRYSTALLINE STYLE, PROTOSTYLE) that abrades against the surface of the gastric shield (and chitinous lining if present) to macerate food particles (figure: Mercenaria mercenaria). R. D. Purchon, in a series of seminal papers (1956, 1957, 1958, 1959, 1960, 1963, 1985, 1987; modified by Dinamani, 1967), categorized bivalve stomachs into various morphological types that are still well recognized, and have been used in the past to define various taxonomic units.
  • TYPE I: stomach type originally described by Purchon (1956) comprising an elongated bipartite chamber; rounded dorsal region including few (2-3) ducts to the digestive diverticula [a former subclass called Oligosyringia by Purchon (1963)], sorting area on right side, cuticularized region (chitinous girdle) on left side, gastric shield, and dorsal hood; elongated ventral region or STYLE SACK, producing an amorphous PROTOSTYLE, with major typhlosole (and accompanying intestinal groove) either not or only simply entering the dorsal chamber, and tapering to a ventral point from which the MIDGUT emerges; characteristic of the DEPOSIT-FEEDING Protobranchia, such as the Nuculoida (Nuculidae), Nuculanoida (Nuculanidae, Yoldiidae), and in simplified form Solemyoida (Solemyidae and Manzanellidae). Purchon (1959) considered this type of stomach characteristic of a group he called Gastroproteia; Villarroel & Stuardo (1998) further divided it into three subcategories according to details of the sorting areas and typhlosoles.###Glos_125
  • TYPE II: greatly simplified stomach type originally described by Purchon (1956) consisting of a large muscular sack, featuring a small to very large esophageal opening, small to absent sorting area, few (2-3) openings (without ducts) to the digestive diverticula (see previous, Oligosyringia), a reduced STYLE SACK (combined or separate from the MIDGUT) producing a short CRYSTALLINE STYLE, with or without a gastric shield and dorsal hood, and with an extensive protective chitinous (scleroproteinaceous) lining; the stomach can be separated from adjacent viscera by a hemocoel, allowing more freedom for crushing action; modified for a carnivorous or scavenging diet, characteristic of the carnivorous "Septibranchia," such as the Poromyoidea (Poromyidae), Cuspidarioidea (Cuspidariidae), and Verticordioidea (Verticordiidae), and of the carnivorous Propeamussiidae. Purchon (1959) considered this type of stomach characteristic of a group he called Gastrodeuteia.###Glos_126
  • TYPE III: stomach type originally described by Purchon (1957) comprising a more-or-less oval dorsal chamber and elongated ventral combined STYLE SACK/MIDGUT, the former chamber featuring a major typhlosole (and accompanying intestinal groove) with a long slender tongue extending into the food sorting CAECUM, numerous scattered ducts to the digestive diverticula [a former subclass called Polysyringia by Purchon (1963)], a CRYSTALLINE STYLE, and a gastric shield; some species with a ciliated groove linking the apex of the tongue of the major typhlosole with the apex of the dorsal hood; characteristic of filter feeders, such as the pteriomorphian Arcoida (Arcidae, Noetiidae, Glycymerididae, Limopsidae, Philobryidae), Mytiloida (Mytilidae), and Pterioida (Pteriidae, Isognomonidae, Malleidae, Ostreidae, Gryphaeidae, and Pinnidae. Purchon (1963, 1987) considered this type of stomach characteristic of a group he called Gastrotriteia.###Glos_127
  • TYPE IV: stomach type originally described by Purchon (1957, 1958) comprising a more-or-less oval dorsal chamber and elongated ventral combined or separate STYLE SACK/MIDGUT, the former chamber featuring a major typhlosole (and accompanying intestinal groove) passing across the floor of the stomach (without extension or deviation), and terminating close to the left pouch, with clustered numerous ducts to the digestive diverticula [see previous, Polysyringia; usually in the left pouch (which serves to further anchor the gastric shield), between the pouch and the major typhlosole, and on the right side of the stomach], a CRYSTALLINE STYLE, and a gastric shield; characteristic of SUSPENSION FEEDERS, such as the pteriomorphian Limoida (Limidae) and Pectinoidea (Pectinidae, Spondylidae, Plicatulidae, Anomiidae), and the heteroconchian heterodont Carditoida (Crassatellidae, Astartidae, Carditidae, Condylocardiidae), Veneroida (some Psammobiidae), Anomalodesmata (Pandoridae, Lyonsiidae, Periplomatidae, Thraciidae), and some Veneroida (Lucinidae, Thyasiridae, some Chamidae, Lasaeidae, Hiatellidae, Gastrochaenidae, some Veneridae, and some Donacidae). Purchon (1959, 1987) considered this type of stomach characteristic of a group he called Gastrotetartika, and ancestral to Types III and V.###Glos_128
  • TYPE V: stomach type originally described by Purchon (1960) comprising a more-or-less oval dorsal chamber and elongated ventral combined or separate STYLE SACK/MIDGUT, the former chamber featuring numerous ducts to the digestive diverticula [see also Polysyringia] concentrated in the left pouch, right and left CAECA, and on the right side of the stomach, a major typhlosole (and accompanying intestinal groove) that is "7-shaped," entering into the right caecum then into the left caecum, a CRYSTALLINE STYLE, and a gastric shield; characteristic of filter feeders, such as most heteroconchian heterodont Veneroida (Ungulinidae, some Chamidae, Trapezidae, Corbiculidae, Cardiidae, most Veneridae, Tellinidae, some Donacidae, Psammobiidae, Semelidae, Solecurtidae, Pharidae, Mactridae, Dreissenidae, Myidae, Corbulidae, Pholadidae, and Teredinidae). Purchon (1959) considered this type of stomach characteristic of a group he called Gastropempta.###Glos_129
STRIA (pl. STRIAE)
General term for a narrow linear furrow or raised sculptural element on a shell surface; also called lines; see also RIB, GROOVE.
STYLE
See CRYSTALLINE STYLE, PROTOSTYLE, STYLE SACK.
STYLE SACK
STYLE SACK fig.Ventral or posterior extension of the STOMACH of many mollusks, including most bivalves, which secretes a rod-shaped inclusion (see also CRYSTALLINE STYLE, PROTOSTYLE) that reduces the size of ingested food particles through rotating abrasion against the gastric shield and, in most mollusks, through the digestive actions of the included enzyme AMYLASE (figure: Mercenaria mercenaria).
SUBEQUAL
Nearly equal.
SUBEQUILATERAL
Nearly EQUILATERAL.
SUBEQUIVALVE
Nearly EQUIVALVE.
SUBLITTORAL
That part of the coastline immediately below the low water mark, and which is never exposed.
SUBMARGINAL LIGAMENT
Type of dorsal LIGAMENT that attaches immediately below the dorsal shell margin on the surface between the two valves.
SULCUS
A large fold or groove.
SUPRABRANCHIAL CHAMBER
SUPRABRANCHIAL CHAMBER fig.Body cavity dorsal to the gills; see also INFRABRANCHIAL CHAMBER (figure: Mercenaria mercenaria).
SUPRAMYAL SEPTUM
Membrane connecting the right and left MANTLE lobes on the dorsal side of the posterior ADDUCTOR MUSCLE; its absence in Malleidae allows the PROMYAL PASSAGE to shunt excurrent water posterodorsally
SUPRASEPTAL CHAMBER
SUPRASEPTAL CHAMBER fig.Body cavity dorsal to the SEPTUM, analogous to SUPRABRANCHIAL CHAMBER in bivalves with non-septibranch gills; see also INFRASEPTAL CHAMBER (figure: Poromyidae).
SUSPENSION-FEEDING
Feeding type of most bivalves during which organic particles are harvested from the water column.
SYNAPOMORPHY
A shared, derived, taxon-defining trait or characteristic.
SYNAPTORHABDIC
Gill type characterized by filaments that are joined together only by tissue junctions, so that the interfilamental spaces are divided into a series of OSTIA or fenestrae; see also EULAMELLIBRANCH, SEPTIBRANCH. Ridewood (1903) defined a group Synaptorhabda based on this character, equivalent to Pelseneer's (1891) Eulamellibranchia plus Septibranchia.
SYNTYPE
Two or more specimens examined by the original author of a species in the original description, but none of which was uniquely designated as the holotype; the entire lot is called a SYNTYPIC SERIES; see also HOLOTYPE, LECTOTYPE, PARATYPE.