Marine Science Dictionary (M-P)

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Madreporite: a plate in echinoderms that allow water in and out

Malacostraca: (class) This is the most diverse class of crustaceans and includes many familiar forms.  There are several important orders

mandible: the lower jaw of gnathostome craniate animals, inermost paired mouthparts of arthropods

mangrove: any of six species of marine trees, the red mangrove dominates tropical estuaries

mantle: the lining of the body of mollusks.  Secretes the calcium carbonate skeleton

marginal sea: any sea mostly connected to its parent ocean

maxilla: the upper jaw bones of gnathostome craniate animals

maxillapeds: "mouth feet" or outer jointed oral appendages of the crustaceans

mediterranean sea: inland sea, body of water open to the ocean but mostly surrounded by land

medusa: a life stage of cnidarians, not represented among the corals and anemones but is the dominant stage of the scyphozoans (true jellyfish)

melon: a fatty organ on the forehead of toothed whales used to focus sound

meroplankton: see plankton

Merostomata: (class) Sub-grouping of the Arthropoda. The horseshoe crabs

meso- (pelagic/benthic): These refer to the upper to middle ranges of the ocean.  The meso zone generally extends from 200m to 1000m. An animal that is benthic and lives in the meso zone would be mesobenthic when a pelagic animal in the meso zone would be mesopelagic

mesoderm: the middle developmental tissue layers, gives rise to many internal organs

migration: usually cyclic movement of organisms.  Migrations may be lateral, as in geographic or vertical, changing places in the habitat or water column

mixed tide: the condition where there are four tidal events, two high and two low per tidal day, of different magnitudes.

Mollusca: (phyla) The mollusks are generally characterized by the presence of a mantle, which in many cases secretes a shell. A muscular foot which has adapted to perform many unique functions in different mollusks. Higher mollusks have developed complex eyes which are similar to the eyes of vertebrates. The Mollusks are second only to the arthropods in species diversity. The marine forms are divided into six major classes... monoplacaphora, polyplacaphora, scaphoda, gastropods, bivalves, cephalopods

molting: see ecdysis

Monoplacophora: (class) Sub-grouping of the Mollusca.  These are simple, ancestral mollusks thought to be extinct until recently

-morph or -morphic:  Gr. prefix or suffix, refers to shape or form as in morphology, "the study of shape or form." mouth brooding

mutation: a random change in an organism's DNA

mutualism: see symbiosis

Myxini: (class) Are marine jawless fishes that lack paired fins, scales, and bone. The Myxini are the hagfishes.  They typically live in deep coastal waters and feed on dead or dying fish. They are noted for there ability to produce copious amounts of mucous, slime, which presumably allows them to bore into there food. Adults (class lack distinguishable eyes


Nansen bottle: a tubular sampling device with ends that snap shut, used for collecting water samples at depth

natural selection: The tendency of animals that are better suited to an environment to produce more offspring that our genetically also more inclined to produce more offspring.  Considered by most to be the most important cause of evolution

neap tide: the weakest tide of the month, occurs around half moon periods, when the Sun-Earth-Moon form a right angle

nekton- nektonic- (gr. Nektos, to swim) Pelagic animals which are able to swim freely against a current

neritic province: This refers to the waters above continental shelf regions.  The majority of life in the ocean lives in the neritic province
see pic

neuston: The plants and animals of the uppermost layer (top millimeters) of the ocean

niche: The sum of the requirements of an individual population or species

nocturnal: During the hours of darkness.  An animal which is active during the hours of darkness.  Contrast with crepuscular and diurnal

nucleic acid: one of four types of organic compounds.  Stores and transfers information withing the cell


oceanic province: This refers to the deeper waters not over, or outside of, the continental shelf regions
see pic

oceanic ridge: plate abduction zones, where new sea floor is being added

oceanic trench: plate subduction zones, where one crustal plate is passing below another

Oligochaeta: (class) sub-grouping of the phyla Annelida.  Oligochaets are charactarized as having few or very small setae they mostly terrestrial and include the earthworms

oligotrophic: a very low level of available nutrients, such as the mid-ocean gyres

omnivore: an animal that eats both plants and other animals

ontogenetic: Otogenetic or ontogenic refers to the changes that occur over an animal or plants lifetime.  For example infant humans feed on liquids only, as adults we do not.  This is an ontogenic change.  Generally organisms develop from less complex forms to more complex forms within their lifetime. Often times the term is used primarily to refer primarily to changes during an embryonic period.  This limits the use of the word as many organisms continue to change throughout their life.  Contrast with phylogenetic

ontogeny: The life cycle or development of an animal or plant from beginning to end.  This is on a brief time scale.  Contrast with phylogeny

open circulatory system: where the circulated body fluids (blood) are not entirley contained in a closed system.  Common in arthropods and annelids.  Contrast to closed circulatory system

organism: a discrete individual within a ecosystem

organic: referring to living material, in chemistry compounds that contain carbon

Osteichthyes: (class) The bony fish, characterized by true bone and paired fins

Ostracoda: (class) These are unusual crustaceans having a jointed clamshell carapace

oviparity: Type of development in which embryos are deposited externally in a egg or egg case and nutrition is provided by a yolk

ovoviviparity: Type of development of embryos in which the young are born live, after having been provided nutrition by a yolk.

oxygen saturation: the amount of oxygen preserved in water relative to the amount that it can actually hold - colder water can hold more oxygen.
parthenogenesis: A type of asecual reproduction wherein the eggs of a femail develope without being fertilized.  Te resulting generation is halploid

pedal disk: the aboral side of polyps attachment of anemones

pelagic: Animals that live in the water column and are not primarily associated with the sea floor are termed pelagic.  Contrast to benthic. See also nektonic and planktonic

pH: the inverse of the log concentration of the hydronium ion, refers to the acidity or alkalinity of a sample.

Phaeophyta: the brown algae

pharyngula: larval stage of chordates

-phagy Gr. suffix, meaning "to eat" as in ovophagous, egg eating

phenotype: the set of characteristics of an organisms in conjunction with the environment

photic zone: The upper levels of the ocean that have enough light for photosynthesis to occur. The actual depth of the water to which light penetrates is dependent on the turbidity of the water

photoautotroph: see autotroph, see photosynthesis

photophore: light producing organs

photosynthesis: A chemical reaction that combines atmospheric or water dissolved carbon dioxide into carbohydrates

phylogenetic: Phylogenetic or phylogenic refers to the changes in animals or plants throughout its evolutionary development.  For example humans used to climb in trees, now we don't this is a phylogenetic change.  Organisms generally develop from less complex to more complex forms.  There are exceptions, however.  Contrast with ontogenetic

phylogeny: The development of an organism throughout its evolutionary development.  This is on a long time scale. Contrast with ontogeny

phytoplankton: any photoautotrophic drifting organism

plankton/planktonic: (gr. Planktos, to drift) Animals which are unable to maintain direction against a current are referred to as the plankton.  These are the ocean drifters.  Planktonic animals range in size from the bacteria to large gelatinous cnidarians and some large fishes such as the oceanic sunfish (genus: Mola).  The Plankton are categorized in different ways.  For example, photosynthesizing plankton are called phytoplankton while animal members of the plankton are called zooplankton.  Many animals have larval forms that are planktonic, while the other stages are nektonic (see nektonic).  These animals which spend only part of there life in the plankton are considered to be meroplankton.  Animals that spend their whole lives as plankton are said to be holoplankton  see pic

plankton sizes: the diviion of planktonic organisms in to groups by size rather than taxonomic or ecological considerations.  see pic
planktotrophic: larval forms that feed in the plankton, less energy is spent on individual offspring and time in the plankton, dispersal time, is increased

plastron: The lower half of the shell of turtles, in sea turtles it is hinged to allow for greater lung capacity

plate tectonics:  theory that the Earth's surface is made up of interlocking plates that are in motion

poikilothermic: see heterothermic

polyp: a life stage in cnidarians, usually benthic and sessile it is the feeding stage of hydrazoans and part of the reproductive cycle of the scyphozoans, while anthozoans only show the polyp stage.  Also used to refer to an individual coral animal

Polychaeta: (class) Sub-grouping of the phylum Annelida. Polychaets are charactarized by numerous setae and pseudopods. They are mostly marine.  The class is further divided into the Orders Errantia (mobile) and the Sedentaia (sessile)

Polyplacophora: (class) Sub-grouping of the Mollusca. These are benthic, usually littoral mollusks with a shell composed of eight jointed plates

population: in ecology, all the individuals of the same species living within a given area

porifera: (phyla) These are the sponges. They are simple sessile invertebrates which respire and obtain food by filtering water through there bodies with currents created by choanocytes (collar cells). They have "skeletons" composed of spongin (a fibrous protein) and or spicules. There are three classes of sponges divided primarily by spicule composition.  The Demospongia are the most common sponges, with skeletons composed of spongin and often siliceous spicules.  The Calcarea are the calcareous sponges, with spicules composed of calcium.  The Hexactinellida are the siliceous sponges, with spicules composed of silicon

precocial: The young of animals born in an advanced stage, generally able to fend for themselves

predation: a type of interactions between individuals, where one gains nutrient value from another

predator: An animal which consumes other animals, a predator which consumes herbivores is said to be a primary predator.  A predator which consumes primary predators is said to be a secondary predator and an animal which consumes secondary predators is said to be a tertiary predator

producer: Any organism which produces its own food,  Usually plants and many bacteria.  Synonymous with autotroph

Prokaryota: organisms that have cells with distinct nuclei.

protandrous: see hermaphroditic protogynous- see hermaphroditic

protein: one of four types of organic compounds that serve as building materials in organisms or to control the rate of chemical reactions (enzymes)

pseudocoelom: a division between the epidermal layers of some organisms that house internal organs.  Nematodes are pseudocoelomate animals

pygynium: The final segment of annelids and arthropods, contain the anus.