- macroalgae
- macrobenthos
- macrochromosome
- macroplankton
- macula
- male
- mammal
- mandible
- mangrove
- manure
- marbled
- mariculture
- marine
- maritime
- marker species
- marsh
- maternal
- mature
- maxilla
- maxillary
- MB
- MCZ
- medial
- mediolateral
- Mediterranean
- meiofauna
- meiosis
- melanism
- melanophore
- membrane
- MEPA
- meristic
- mesad
- mesal
- mesial
- mesic
- mesodemersal
- mesoderm
- mesohaline
- mesopelagic
- Mesozoic
- metabolism
- metacentric
- metahaline
- metamorphic
- metamorphosis
- metazoa
- microchromosomes
- micropaleontology
- micropyle
- midbelt
- midgut
- midwater
- migrant
- migration
- milt
- mimicry
- Miocene
- mitosis
- mixo-mesohaline
- mixo-oligohaline
- MMF
- MNHN
- molar
- mollusc
- MOM
- monoculture
- monoecious
- monogamy
- monograph
- monophyletic
- monotypic
- montane
- morpha
- morphological
- morphology
- morphometric
- morphometry
- mottle
- mouth
- MRAC
- MSNG
- MSNM
- mucous
- mud
- mudflats
- mugilids
- multifurcate
- MUT
- mutant
- myomeres
- myoseptum
- myotome
- mysid
- MZUF
- MZUT