Glossary, continued. 



MORTALITY — Death rate expressed as a proportion 

 of a population or community of organisms. Mortality 

 is caused by a variety of sources, including predation, 

 disease, environmental conditions, etc. 



MOTILE — Capable of or exhibiting movement or loco- 

 motion. 



MUTUALISM — An interaction between two species 

 where both benefit. Some authorities consider true 

 mutualism to be obligatory for both species, while 

 mutually beneficial relationships that are not essential 

 for either species are classified as protocooperative. 



NIDAMENTAL APPARATUS— A pair of glands that in 

 squids and their allies lies in the mantle cavity, with their 

 openings situated close to the oviductal outlet(s). This 

 structure secretes a mucinous material that aids in the 

 encapsulation of eggs as they leave the oviduct. 



NOCTURNAL — Refers to night, or animals that are 

 active during the night. 



NUDIBRANCH — A group of shell-less marine mol- 

 luscs commonly known as sea slugs. 



OCEANIC — Living in or produced by the ocean. 



NACREOUS MATERIAL— A calcareous, lustrous se- 

 cretion in the inner surface of the shell of many mol- 

 luscs. Foreign particles lodging between the inner 

 shell surface and mantle are covered by nacre, often 

 forming pearls. 



NANOPLANKTON — Microscopic, planktonic organ- 

 isms smaller than 20 microns in diameter. 



NATAL — Pertaining to birth or hatching. 



NAUPLIUS — A free-swimming larva, the first stage in 

 the development of certain crustaceans such as 

 shrimps. 



NEARSHORE — Consists of those waters extending 

 from the beach out to 6 fathoms of depth. 



OCEANIC ZONE— Pelagic waters of the open ocean 

 beyond the continental shelf. See BATHYPELAGIC, 

 EPIPELAGIC, ABYSSOPELAGIC, MESOPELAGIC, 

 and NERITIC. 



OLIGOHALINE — A category in the Venice system of 

 estuarine salinity classification; water with salinity of 

 0.5 to 5.0 parts per thousand (% ). 



OMNIVORE — An animal that eats both plant and ani- 

 mal matter. 



OOCYTES — The cells in ovaries that will mature into 

 eggs. 



OSMOREGULATION— The maintenance of proper 

 water and electrolyte balance in an organism's body. 



NEKTONIC— Refers to pelagic animals that are strong 

 swimmers, live above the substrate in the water col- 

 umn, and can move independently of currents. 



OSTRACODS— A class of widely distributed marine 

 and freshwater crustaceans whose bodies are com- 

 pletely enclosed in a bivalve carapace. 



NEMERTEA — A phylum of unsegmented, elongate 

 marine worms having a protrusible proboscis and no 

 body cavity, and live mostly in coastal mud or sand; 

 nemerteans. 



NERITIC — An oceanic zone extending from the mean 

 low tide level to the edge of the continental shelf. See 

 INNER SHELF, LITTORAL, and OCEANIC ZONES. 



NEUSTON — Organisms that live on or just under the 

 water surface, often dependent on surface tension for 

 support. 



NICHE — The fundamental niche is the full range of 

 abiotic and biotic factors under which a species can live 

 and reproduce. The realized niche is the set of actual 

 conditions under which a species or a population of a 

 species exists, and is largely determined by interac- 

 tions with other species. 



OTOLITHS— Small calcareous nodules located in the 

 inner ear of fishes used for sound reception and 

 equilibration. They are often used by biologists to 

 assess daily or seasonal growth increments. 



OUT-MIGRATION— Movement of animals out of or 

 away from an area (e.g., juvenile sciaenids moving 

 from estuaries to the ocean). 



OVIGEROUS— The condition of being ready to re- 

 lease mature eggs; egg-bearing. 



OVIPAROUS— Refers to animals that produce eggs 

 that are laid and hatch externally. See OVOVIVIPA- 

 ROUS and VIVIPAROUS. 



OVIPOSITION— The process of placing eggs on or in 

 specific places, as opposed to randomly dropping or 

 broadcasting them. 



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