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.

L

LABIAL PALPS
LABIAL PALPS fig.Paired lamellae on either side of the mouth, usually with ridged and ciliated opposing surfaces (figure: Mercenaria mercenaria). Junctions of the distal oral groove (DOG) of the palps with the ventral tips of the anterior ctenidial filaments (ACF) of the inner demibranchs were categorized by Stasek (1963) as:
  • CATEGORY I: ACF inserted but not fused into the DOG, occurring in such families as Mytilidae, Astartidae, and some Crassatellidae.
  • CATEGORY II: ACF inserted into and fused with the DOG, occurring in such families as Limidae, Carditidae, Lyonsiidae, Chamidae, Hiatellidae, Cardiidae, Gastrochaenidae, most Veneridae, Pharidae, Dreissenidae, and Pholadidae.
  • CATEGORY III: ACF not inserted into the DOG (and thus not fused), although the anteroventral margin of the inner demibranchs can be fused to the inner palp lamellae, occurring in such families as Arcidae, Noetiidae, Limopsidae, Philobryidae, Isognomonidae, Malleidae, Ostreidae, Gryphaeidae, Pinnidae, some Limidae, Pectinidae, Propeamussidae, Spondylidae, Plicatulidae, Anomiidae, some Crassatellidae, Pandoridae, Periplomatidae, Thraciidae, Verticordiidae, Poromyidae, Cuspidariidae, Lucinidae, Ungulinidae, Thyasiridae, Lasaeidae, Trapezidae, some Veneridae, Corbiculidae, Tellinidae, Psammobiidae, Semelidae, Solecurtidae, Mactridae, Myidae, Corbulidae, and Teredinidae.
LACUNA (pl. LACUNAE)
A space or hemocoel within tissues, serving in place of vessels for the circulation of body fluids; here, the kidneys in Verticordiidae are accompanied by an extensive lateral system of lacunae.
LAMELLA (pl. LAMELLAE)
Thin plate-like or scale-like structure.
LAMELLIBRANCHIA
Bivalvia.
LATERAL BULBS
Elaborations of the LIPS in Lyonsiidae.
LATERAL TEETH
LATERAL TEETH fig.HINGE TEETH in a HETERODONT hinge that are far removed from the UMBO (as opposed to CARDINAL TEETH below the umbo) at the anterior and/or posterior ends, usually oriented parallel to the shell margin and serving to prevent anteroposterior "sliding" or movement of the valves when closed (figure: Polymesoda floridana).
LECITHOTROPHIC
Larval development type characterized by a free-swimming stage (VELIGER) that carries its own nutritional reserves and does not feed in the plankton.
LECTOTYPE
A single specimen serving the function of a HOLOTYPE, designated by a subsequent author from the members of a syntypic series; the remaining syntypes become PARALECTOTYPES or the equivalents of paratypes by this action; see also HOLOTYPE, PARATYPE, SYNTYPE.
LENGTH
Distance between anterior and posterior margins.
LIGAMENT
Elastic uncalcified structure, comprised of two layers (lamellar of organic composition, and fibrous of organic material plus aragonite], usually brown to black in color, that connects the two bivalve shells at the HINGE line and functions as a spring to open the valves when the ADDUCTOR MUSCLES relax; either EXTERNAL (dorsal to the hinge teeth, visible and under tension when the valves are closed) or INTERNAL (ventral to the hinge teeth, not visible and under compression when the valves are closed) or both.
LIGAMENTAL PIT
See RESILIFER.
LIPS
Outgrowths of the buccal dermis (integument surrounding the mouth), which are usually simple flaps dorsal and ventral of the mouth , but hypertrophy into arborescent or ruffled structures in Pectinidae, Limidae, and Spondylidae; in some limid species, the dorsal and ventral lips are fused, leaving only a series of ostia as mouth openings; hypertrophied lips serve as filters of potential food particles.
LITHODESMA
LITHODESMA fig.Unpaired calcareous structure usually at the center of the inner LIGAMENT layer of the otherwise uncalcified internal ligament (RESILIUM) of some bivalves, especially the Anomalodesmata; in some families (e.g., Periplomatidae, Thraciidae) it is free and bridges the valves adjacent to the CHONDROPHORE; also called calcareous ossicle or osciculum (figure: Periploma planiusculum).
LITTORAL
Intertidal, or the coastal zone between the highest high-water mark and the lowest low-water mark.
LUNULE
LUNULE fig.Heart- or crescent-shaped impressed external feature, often demarcated and differently sculptured from the main body of the shell, located anterodorsally on the shell of some bivalves (e.g., Veneridae) anterior to the UMBONES (figure: Periglypta listeri).