Keel - Carina or ridge. A prominent, sharply raised rib, generally marking an abrupt change of slope in the shell outline. See carina.
Kelp - member of brown algal order Laminariales
Kinetoplast - a disk-shaped mass of circular DNAs
Labiate - having lips or parts that resemble lips
Labrum - The upper lip of an arthropod.
Lacustrine - living near lakes
Lagoon - a body of shallow salt or brackish water separated from the deeper sea by a shallow or exposed sandbank, coral reef, or similar feature.
Lamella (lamellae) - gill filament
Lamellate - Covered with scales or thin plates.
Lamina - flattened leaf-like blade
Lampricide - a chemical which is designed to target the larvae of Lampreys in river systems before their recruitment as parasitic adults.
Lanceolate - Long and spearhead-shaped.
Lancoelate leaves - Leaves having a rounded base tapering towards a pointed tip.
Larva (pl. larvae) - The immature, wingless form of many insects that hatches from the egg. The larva then transforms into a pupa, and then metamorphoses into the adult form.
Larval shell - shell of a molluscan larva before it undergoes metamorphosis, usually set off by a change of sculpture.
Lateral - (adj) Situated at or extending to the side.
Lateral line - a sense organ used to detect movement and vibration in the surrounding water.
Lentic - (adj) Inhabiting still waters such as lakes, ponds or swamps
Lentic - standing-water environments (e.g., lakes, wetlands, temporary pools).
Lenticular - Having the shape of a double convex lens.
Lesion - (n) A wound or injury.
Lethargic - deficient in alertness or activity
Leucoplast - colorless, usually starch-containing plastid
Life Cycle - A life cycle is a period involving one generation of an organism through means of reproduction, whether through asexual reproduction or sexual reproduction.
Ligament area - In some bivalves, the area between the umbones containing the external ligament.
Limnetic zone - open-water, deeper areas of a lake or pond, away from the littoral zone.
Lipopolysaccharide - large molecules consisting of a lipid and a polysaccharide joined by a covalent bond.
Lirate - finely lined
Littoral - (adj) near the shore, intertidal
Littoral zone - area of a waterbody shallow enough for growth of rooted aquatic vegetation.
Locomotory - motive
Loculus - a small cavity or space within an organ or in a plant or animal
Lophophore - (n) Horseshoe-shaped feeding organ with filament appendages used to gather food.
Lorica - a hard protective sheath
Lotic - running-water environments (e.g., streams, springs).
Lysis - (n) The breaking open of a cell by the destruction of its wall or membrane (v. Lyse)
Macroalga - (n) Large alga that can be easily seen. E.g. kelp.
Macronucleus - large nucleus
Macrophytes - (n) Plants of lakes, streams and wetlands that are visible with the naked eye.
Macroscopic - Barely visible to the naked eye.
Macrothallus - large, conspicuous phase of organisms's life history
Malacology - The branch of zoology that deals with the mollusk, the animal within the shell.
Malacozoology - The study of living mollusks in relation to their animate and inanimate environment.
Malleated - Surface having a hammered appearance.
Mandibles - Paired, pincer-like hardened mouthparts (jaws) in arthropods, which are used to grasp, tear, and push food into the mouth.
Mantle (diatom) (n) - a surface of the valve.
Mantle cavity - The space between the mantle and the visceral mass.
Mantle scar - A broad area of attachment of the mantle edge in bivalves (e.g., sportella), too wide to be called a pallial line.
Manubrium - the bulla can be divided into two main parts, the handle or manubrium and the anchor. The two parts are not always clearly delimited. The manubrium connects the maxillary arms (via two ducts) with the anchor.
Margin - edge
Margin of opercle - Edge of the operculum or gill covering.
Marginal processes - projections from the edge of a cell or cell wall
Marl - a byproduct of photosynthesis formed when bicarbonate is used
Marsupium - Structures in invertebrates for enclosing or carrying eggs or young.
Mature - An individual that has reached the age for reproduction.
Maxilla - the fifth and last pair of cephalic appendages. Historically referred to as the second maxilla.
Maxilliped - the first pair of thoracic appendages, located on the last somite of the cephalosome. Uniramous and typically modified for feeding or grasping.
Maxillule - the fourth cephalic appendage. Historically referred to as the first maxilla.
Maximum - most, highest (plural maxima)
Medial - (adj) Dividing an animal into right and left halves.
Medulla - central tissue of thallus
Meiosis - nuclear division in which chromosome number is reduced from diploid to haploid, genetic segregation of chromosomes
Meristem - (n) A group or region of cells dividing rapidly and initiating growth.
Meristematic - (adj) Describing tissue in a distinct region of a plant that is actively, or potentially active, in the process of cell division
Meroplankton - organisms that spend part of their life cycle as plankton and part on the benthos
Mesentery - a double layer of peritoneum that attaches to the back wall of the abdominal cavity and supports the small intestines.
Mesial (mesal) - pertaining to the middle or in the direction of the middle.
Mesially - (adj) Of, in, near, or toward the middle.
Meso-eutrophic - (adj) A productive status between moderate productivity
Mesohaline - (adj) Describing intermediate levels of salinity between freshwater and seawater, about 15ppt (parts per thousand)
Mesohaline - Moderately brackish water with a salinity range of 5-18 ppt.
Mesokaryotic - having chromosomes that persist in condensed form at all times, the condition of the dinoflagellate nucleus
Mesoplax (Metaplax) - An accessory plate behind the umbones of some Pholadacea.
Mesothermal (mineralogy) (adj.) - Of a hydrothermal mineral deposit, formed at great depth at temperatures of 200-300°C.
Mesotrophic - (n) Lakes have moderate levels of nutrients and algae. Metabolic
Metamorphosis - (n) The marked and rapid transformation of a larva into an adult that occurs in some animals.
Metasoma - posterior part of the body
Metasomal wings - posterior lateral projections from the last somite of the metasome of some copepods.
Metasome - includes the somites of the copepod body anterior to the major body articulation. The metasome bears the second through fifth pairs of legs in calanoids, and the second through fourth pairs of legs in cyclopoids, harpacticoids, and poecilostomes.
Micron - (n) A unit of length. One Micron = 39 millionths of an inch = one-millionth of a meter.
Microphagous - Consuming microscopic food.
Microthallus - the tiny, inconspicuous stage of an organism's life history, alternating with the macrothallus stage
Microvilli - microscopic, finger-like projections
Mitochondria - an organelle containing enzymes responsible for producing energy
Mollusca (Mollusk) - Soft-bodied, highly developed animals without a backbone and with an exterior or interior shell.
Molluscivorous - eating mollusks
Molt / Molting - A process where crustaceans and insects shed their exoskeleton (external support). This is an important growth process, enabling the animal's body to expand.
Mono - one
Monoecious - (adj) having male and female reproductive organs in the same plant or animal. Literally ‘one house’.
Monogenea - a group of largely ectoparasitic members of the flatworm
Monosiphonous - made of a single siphon or tube
Monostromatic - blade composed of a single layer of cells
Monotypic - a genus having only one species
Moorland - (n) a type of habitat found in upland areas, characterized by low growing vegetation on acidic soils.
Morph - type
Morphological - (adj) Related to the observable shape or anatomy of an organism.
Motile - (adj) Capable of self-propelled movement
Mottled - (adj) having spots or patches of color.
Mouthparts - the group of appendages near the mouth which are involved in feeding, comprising the paired mandibles, maxillules, maxillas, and maxillipeds.
Mucilage - (n) A gelatinous substance, a glob of mucous
Mucilaginous - having the sticky properties of an adhesive
Multialxial - axis composed of multiple, longitudinal filaments, each derived from one apical cell
Multiseriate - (adj) Occurring in more than one series (row)
Murolith - heterococcolith with an elevated rim but without well developed shields
Mutant - an organism that has characteristics resulting from chromosomal alteration
Myxosporea - a class of microscopic parasites, belonging to the Myxozoa. They have a complex life cycle which comprises vegetative forms in two hosts, an aquatic invertebrate (generally an annelid) and an ectothermic vertebrate, usually a fish.