Glossary, continued. 



DIRECT DEVELOPMENT— See EMBRYONIC DE- 

 VELOPMENT. 



EPIBENTHIC — Located on the bottom, as opposed to 

 in the bottom. 



DISPERSAL — The spreading of individuals through- 

 out suitable habitat within or outside the population 

 range. In a more restricted sense, the movement of 

 young animals away from their point of origin to loca- 

 tions where they will live at maturity. 



DISSOCHONCH— The adult shell secreted by newly- 

 settled clam larvae or plantigrades. 



DISTRIBUTION— (1 ) A species distribution is the spa- 

 tial pattern of its population or populations over its 

 geographic range. See RANGE. (2) A population 

 depth distribution is the proportion or number of all 

 individuals, or those of various sizes or ages, at differ- 

 ent depth strata. (3) A population age distribution is the 

 proportions of individuals in various age classes. (4) 

 Within a population, individuals may be distributed 

 evenly, randomly, or in groups throughout suitable 

 habitat. 



DIURNAL — Refers to daylight activities, or organisms 

 most active during daylight. See DIEL. 



ECHINODERMATA— A phylum of radially-symmetri- 

 cal marine animals, possessing a water vascular sys- 

 tem, and a hard, spiny skeleton (e.g., sea stars, sea 

 urchins, and sand dollars). 



ECTOPARASITE— A parasite that attacks (and usu- 

 ally attaches to) a host animal or plant on the outside. 

 Feeding periods and/or attachment time may be brief 

 compared to internal (endo-) parasites. 



EELGRASS — Vascular flowering plants of the genus 

 Zostera that are adapted to living under water while 

 rooted in shallow sediments of bays and estuaries. 



EMBRYONIC DEVELOPMENT— The increase in cell 

 number, body size, and complexity of organ systems 

 as an individual develops from a fertilized egg until 

 hatching or birth. In direct development, individuals at 

 birth or hatching are essentially miniatures of the 

 adults. In indirect development, newly hatched indi- 

 viduals differ greatly from the adult, and go through 

 periodic, major morphological changes (larval stages 

 and metamorphosis) before becoming a juvenile. 



EMIGRATION— A movement out of an area by mem- 

 bers of a population. See IMMIGRATION. 



ENDEMIC — Refers to a species or taxonomic group 

 that is native to a particular geographical region. 



EPIDERMAL — Refers to an animal's surface or outer 

 layer of skin. 



EPIFAUNA — Animals living on the surface of a sub- 

 strate. 



EPIPELAGIC — The upper sunlit zone of oceanic water 

 where phytoplankton live and organic production takes 

 place (approximately the top 200 m). SeeEUPHOTIC. 



EPIPHYTIC — Refers to organisms which live on the 

 surface of a plant (e.g., mosses growing on trees). 



EPIPODAL — A structure or location associated with 

 the leg or foot; typically refers to arthropod anatomy. 



ESCARPMENT— A steep slope in topography, as in a 

 cliff or along the continental slope. 



ESTUARY — A semi-enclosed body of water with an 

 open connection to the sea. Typically there is a mixing 

 of sea and fresh water, and the influx of nutrients from 

 both sources results in high productivity. 



EUHALINE— A category in the Venice system of es- 

 tuarine salinity classification; water with salinity of 30 to 

 40 parts per thousand (%o). 



EUPHOTIC— Refers to the upper surface zone of a 

 water body where light penetrates and phytoplankton 

 (algae) carry out photosynthesis. See EPIPELAGIC. 



EURYHALINE— Refers to an organism that is tolerant 

 of a wide range of salinities. 



EURYTHERMAL— Refers to an organism that is toler- 

 ant of a wide range of temperatures. 



EXTANT — Existing or living at the present time; not 

 extinct. 



FAUNA — All of the animal species in a specified re- 

 gion. 



FECUNDITY— The potential of an organism to pro- 

 duce offspring (measured as the number of gametes). 

 See REPRODUCTIVE POTENTIAL. 



FILTER FEEDER— Any organism that filters small 

 animals, plants, and detritus from water or fine sedi- 

 ments forfood. Organs usedforfiltering include gills in 

 clams and oysters, baleen in whales, and specialized 

 appendages in crustaceans and marine worms. 



344 



