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M

macroevolution

Evolution happening on a large scale, i.e., at or above the level of species, over geologic time resulting in the formation of new taxa.

mantle

The external fold, or folds, of the soft, exterior membrane of the body of a bivalve, that secretes the shell and usually forms a cavity enclosing the gills and other organs.

metamorphosis

A change in body form and often habits of an animal following the embryonic stage during normal development. (pl. metamorphoses)

microevolution

Evolution involving small-scale changes, i.e., within the species level, occurring over a short period of time that results in the formation of new taxa.

microscopic anatomy

The branch of anatomy in which the structure of cells, tissues, and organs is studied with a light or electron microscope.

mimicry

A phenomenon in which an individual gains some sort of survival advantage by looking like an individual of another (often more harmful) species.

Modern Synthesis

The union of ideas from several biological specialties that formed a sound account of evolutionary theory. This synthesis has been generally accepted by most working biologists. The Synthesis was produced over approximately one decade (1936–1947), stimulated by the development of population genetics (1918–1932). This showed that Mendelian genetics was consistent with natural selection and gradual evolution. The Synthesis is still, to a large extent, the current paradigm in evolutionary biology.

molecular clock

A technique in the field of molecular biology that calculates the time of species divergence from the number of molecular differences present in the species’ DNA sequences or proteins.

Mollusca

The phylum of the animal kingdom, including the classes Cephalopoda, Gastropoda, Bivalvia, Scaphopoda, Polyplacophora, Monoplacophora, Caudofoveata, and Solenogastres. These animals have an unsegmented bilateral body, with most of the organs and parts paired, but not repeated serially. Mollusks are defined by a tissue called the mantle, which forms the shell and encloses most organs. Most mollusks possess a calcareous shell, which can be univalve, bivalve, or multivalve.

mollusk

A member of the phylum Mollusca; also spelled mollusc (most especially in the United Kingdom).

mutation

A change in the nucleotide sequence of genetic material whether by substitution, duplication, insertion, deletion, or inversion.

mutualism

An interaction between members of two species which benefits both; in strict terms, obligatory mutualism occurs when neither species can survive under natural conditions without the other.

mytiliform

Mussel-shaped.