- Macrophyte
- any large living marine plant such as algae, sea grasses, mangroves
- Madroporite
- sieve-like button-shaped process on top surface of Echinoderms that serves as the external opening of the water vascular system
- Mammal
- any member of the Class Mammalia; warm-blooded, have hair, have live births, nurse their young, breath air, have a 3 part inner ear structure; e.g., whales, bears, humans
- Mangrove
- variety of salt tolerant trees and shrubs that inhabit the intertidal zone of tropical and semi-tropical regions
- Mantle
- portion of the body wall in mollusks that lines and secretes the shell or forms the body wall
- Marine
- pertaining to or inhabiting the sea, ocean, or other salt water
- Marsh
- area of wetland periodically flooded by water and colonized by marsh grasses and other marsh plants
- Marsh plain
- coastal area that is raised above the highest tide level and has become dry
- Marsupial
- mammal in which the embryonic young are born, travel to a pouch on the mother's abdomen, and attach to a nipple to complete development
- Mean sea level
- average level of all the tides
- Medusa
- adult bell or umbrella shaped form of cnidarians; includes fresh and salt jellies; the sexual free-swimming form; Spanish word for jelly is medusa
- Melanistic
- color phase in which the skin, plumage, or pelage is black or near black due to the presence of the pigment melanin
- Melon
- fatty cushion structure in the forehead region of toothed whales and dolphins that is used during echolocation
- Mermaid’s purse
- leathery egg case laid by some cartilaginous fishes; largely composed of keratin
- Mesoglea
- middle jelly, the substance between the inner and outer dermal layers of a jelly's bell; consistency is species dependent; gives jelly its common name
- Metabolism
- physical and chemical changes within a living organism involved in the maintenance of life
- Microorganism
- any microscopic organism
- Midden
- refuse heap; commonly used to describe the garbage heaps of ancient Native American villages
- Migration
- periodic and often habitual movement of animals from one area to another for purposes of breeding and eating
- Milt
- secretions from male reproduction organs of fishes
- Mimicry
- superficial resemblance of one organism to another or to objects in its environment for concealment or protection
- Mollusk
- any member of the Phylum Mollusca; invertebrates with a soft unsegmented body, often somewhat enclosed by a shell; e.g., abalone, snails, clams, slugs, and cephalopods
- Molt
- periodic shedding of exoskeleton, hair, feathers, and/or skin that allow new growth to take place underne
- Monoecious
- male and female parts on the same plant
- Monogamy
- mating with only one partner
- Morphology
- body structure and form of an organism
- Mudflat
- expanses of mud that are periodically exposed to low tide and are usually adjacent to salt marshes
- Mustelid
- any member of the family Mustelidae; carnivorous mammals that secrete a musky odor and often show delayed inmplantation
- Mutualism
- symbiotic close association between two organisms in which each derives some benefit
- Myoglobin
- red iron containing and oxygen carrying protein pigment found in the muscles of vertebrates
