- macrobenthos
- macroplankton
- Madeira Islands
- male
- Malta Islands
- mammals
- mandible
- marbled
- marine
- Marmara Sea
- mature
- maxilla
- MB
- MCZ
- medial
- mediolateral
- Mediterranean
- melanism
- melanophore
- membrane
- MEPA
- meristic
- mesodemersal
- mesopelagic
- metamorphic
- midbelt
- midwater
- migrant
- MMF
- MNHN
- molar
- mollusc
- MOM
- monoecious
- monotypic
- morphological
- morphometry
- mottle
- mouth
- MRAC
- MSNG
- MSNM
- mucous
- MUT
- myomeres
- mysid
- MZUF
- MZUT