Macroalgae – algae over 1mm long.

Macrobenthos – benthos over 1mm long.

Macroinvertebrates – by practical definition those aquatic invertebrates generally visible to the unaided eye and retained by a U.S Standard No. 30 sieve (0.59 mm mesh opening).

Macrourid – grenadier fish, having an elongate tapering body and a compressed pointed tail; of the family Macrouridae.

Madreporite – sieve plate; small porose button on upper or aboral surface of the body ring of starfish, through which the water vascular system connects with the exterior.

Mantle – solid but plastic layer between crust and core of earth.  In molluscs the dorsal body wall covering the viscera and secreting the shell.

Median – middle; lying on the midline (of the body or body part).

Medusa – the sexual stage of Hydrozoa and Scyphozoa.

Meiobenthos – benthos from 1mm to 0.1mm long.

Melon – in many toothed whales, it is the bulging forehead containing oil, muscles, and nasal air sacs and passages.  Believed to be used in the focusing or sounds for echolocation.

Meroplankton – temporary plankton.

Mesal – median.

Mesopelagic – Between epi- and bathypelagic zones at 200-1000 m depth.

Mesothermal – in general, pertaining to waters ranging in temperature between 15-30 C.

Mesothrophic – waters with moderate amounts of nutrients and organic materials.

Mesoxyphilous – occurring in waters with moderate concentrations of dissolved oxygen.

Microbenthos – benthos less than 0.1 mm long.

Microphagous – feeding on small particles.

Micron – one thousandth of a millimetre.

Mid Ocean Ridge – a system of rifts and mountains ranges in oceans where ocean floor spreading occurs and upwelling of new rock takes place.

Mixotrophic – able to exist autotrophically or geterotrophically.

Morphology – the science of form or structure.

Multiplate – (also multiple-plate) a type of artifical substrate sampler, usually consisting of a number of pressed hardboard plates mounted on a rod or bolt.

Nacreous – pearly, with iridescent lustre.

Nannoplankton – phytoplankton 5-60 microns long.

Nauplius – larval stage of many crustacean.

Neap Tide – tide of lowest amplitude in lunar cycle.

Nearctic – the biogeographic region including Greenland and the continent of North America south to the Tropic of Cancer.

Nekton – active pelagic swimming animals.

Nematocyst – stinging cells of coelenterates.

Neritic – relating to waters over continental shelves.

Net production – production going to biomass increase.

Neuston – organisms of the water surface film.

Nodulate – knotty; having small knots or swelling.

Nodulose – covered with small knobs or lumps.

Nyctoepipelagic – migrating from deeper waters to the epipelagic zone at night.

Oblique – slanted.

Occipital – on or pertaining to the posterior part of the head.

Oceanic – the pelagic environment beyond continental shelves.

Oligotrophic – aquatic areas of low productivity.

Oligoxyphilous – characteristic of water having low dissolved oxygen concentrations.

Ooze – soft deposits of the ocean bottom.

Operculum – horny or calcareous plate (or plates) covering the main opening or aperture of the shell, as in barnacles and certain gastropods.

Ostracod – small, active mostly freshwater crustacean having a carapace covering and seven pairs of appendages; of the subclass Ostracoda.

Ovoid, ovate – egg-shaped; oval.

Ovoviviparous – “live-bearing” fish.  Eggs are held within the body of the female where the development of the embryo takes place.

Oviparous – producing eggs that develop and hatch outside the female’s body.

Pallets – pair of slender, plume-like rods which close the burrow of the shipworm when siphons are withdrawn.

Pallial line – a single-line impression on the inner surface of the valve parallel to the outer margin, marking the attachment of the muscular edge of the mantle.

Pallial sinus – wide indentation of the pallial line, at the posterior end, below the muscle scar, marking passage of siphon.

Palmate – like the palm of a hand with finger-like processes.

Papilla (papillae) – a soft, fleshy projection, usually small and nipple-like.

Parietal – wall-like; side (as in outer shell plates of barnacles).

Patch reefs – small coral reefs without lagoons.

Pec-slapping – raising a pectoral fin out of the water and slapping it noisily against the water surface.

Pectinate – with branches or processes like the teeth of a comb.

Pectoral fins – also called flippers, paired, paddle-shaped forelimbs, used for stability and steering.

Peduncle – normally called the caudal peduncle, it is the tail region.

Pelagic – having to do with or living in the open seas or oceans; not associated with the seabed or coastal areas.

Pennate – elongate.

Periostracum – outer horny layer of the shell.

Petiole – a stalk or stem by which something is attached.

Photosynthesis – the synthesis of organic compounds from inorganic carbon using light as an energy source.

Phylogeny – the evolution of a genetically related group of organisms.

Phytoplankton – plant plankton.  Phytoplankton carries out photosynthesis and is the basis of the aquatic food chain.

Plankton – minute aquatic organisms that float or drift near the surface in the open sea.  Plankton comprises plant (phytoplankton) and animal (zooplankton) organisms.

Plumose – feather-like.

Pod – long-term social group of whales.

Polychaetes – a class of marine worms and their free-swimming larvae.

Polyp – a coelenterate having a hollow cylindrical body closed at one end and opened at the other with a central mouth surrounded by tentacles armoured with nematocysts.

Population – individuals of one species.

Pores – small tubular cavities in wall plates of barnacles, the ends of which may be viewed from below.

Porpoising – leaping clear of the water when surfacing to breathe, while at the same time moving forward at speed.

Posterior – rear; hinder.

Predaceous – attacking and feeding on other animals.

Primary consumers – herbivores.

Primary producers – photosynthetic plants. Autotrophs.

Producers – organisms carrying on photosynthesis.

Protandrous – sequential hermaphrodite in which the organism is first a male and later a female.

Protogynous – sequential hermaphrodite in which the organism first functions as a female and later as a male.

Proximal – toward the point of attachment.

Pteropods – a group of tiny marine snails having the anterior lobes of the foot expanded into broad, line, wing-like swimming organs.  They live like plankton.

Purse-seine netting – the use of a net up to 2 km long and 100 m deep to encircle a shoal of fish.  The bottom is then drawn up to form a “purse” with the animals trapped inside.

Pycnocline – zone of rapid vertical density change in water.