Glossary, continued. 



LITTORAL — The shore area between the mean low 

 and high tide levels. Water zones in this area include 

 the littoral pelagic zone and the littoral benthic zone. 



MACROALGAE — Relatively large, multicellular, non- 

 vascular marine or estuarine plants that float, drift 

 along the bottom, or have hold-fasts that anchor them 

 to sand, rock, or shell. Larger than and different from 

 planktonic or benthic unicellular (micro-) algae. 



MANTLE — The upper fold of skin in molluscs that 

 encloses the gills and most of the body in a cavity 

 above the muscular foot. In squids and allies, the 

 mantle is below the body and behind the tentacles 

 (derived from the foot) due to the shift in the dorsal- 

 ventral axis. The mantle produces the shell in species 

 having them. 



MANTLE LENGTH— The total length of the mantle of 

 squids and allies. 



MARICULTURE — The rearing of marine vertebrates, 

 invertebrates, or algae, to be harvested for commercial 

 or subsistence purposes. See AQUACULTURE. 



MARINE — Of, pertaining to, living in, or related to the 

 seas or oceans. 



MARSH — Plant community developing on wet, but not 

 peaty, soil in either tidal or non-tidal areas. 



MEAN LOWER LOW WATER (MLLW)— The arith- 

 metic mean of the lower low water heights of a mixed 

 tide over a specific 1 9-year Metonic cycle (the National 

 Tidal Datum Epoch). Only the lower low water of each 

 tidal day is included in the mean. 



MEDUSA — A free-swimming sexual form in coelenter- 

 ates. 



MEG ALOPA — The larval stage of a crab characterized 

 by an adult-like abdomen, thoracic appendages, and a 

 developed carapace; occurs afterthe zoeal stage. See 

 ZOEA. 



MEIOFAUNA — Very small animals, usually < 0.5 mm 

 in diameter, and often planktonic. 



MELANOPHORE — A pigment cell containing melanin 

 that is present in many animals and is responsible for 

 pigmentation and color changes. 



MERISTIC — Refers to countable measurements of 

 segments or features such as vertebrae, fin rays, and 

 scale rows. Counts of these are used in population 

 comparisons and classifications. 



MEROPLANKTON — Temporary plankton, consisting 

 of eggs and larvae; seasonal plankton. 



MESOHALINE — A category in the Venice system of 

 estuarine salinity classification; water with salinity of 5 

 to 18 parts per thousand (%o). 



MESOPELAGIC — Ocean zone of intermediate depths 

 from about 200-1 ,000 m below the surface, where light 

 penetration drops rapidly and ceases. 



METAMORPHOSIS— Process of transforming from 

 one body form to another form during development 

 (e.g., tadpole changing to a frog). See EMBRYONIC 

 DEVELOPMENT. 



METRIC TON (t)— A unit of mass or weight equal to 

 2,204.6 lb. 



MIGRATION — Movement by a population orsubpopu- 

 lation from one location to another (often periodic or 

 seasonal, and over long distances). Vertical migra- 

 tions in the water column may be daily or seasonal 

 within the same area. Migrations between deep and 

 shallow areas are usually seasonal and related to 

 breeding. Many marine birds and mammals have 

 seasonal latitudinal migrations associated with breed- 

 ing. See EMIGRATION, IMMIGRATION, RANGE, and 

 RECRUITMENT. 



MILT — The seminal fluid and sperm of male fish. 



MIXING ZONE — The portion of an estuary with annual 

 depth-averaged salinities of 0.5 to 25 parts per thou- 

 sand (%o). 



MOLLUSC — Any invertebrate of the phylum Mollusca, 

 unsegmented animals with a body consisting of a 

 ventral foot and a dorsal visceral mass. Most possess 

 a mantle which secretes a calcareous shell. Common 

 representatives are snails, mussels, clams, oysters, 

 and squid. 



MOLT — The process of shedding and regrowing an 

 outer skeleton or covering at periodic intervals. Crus- 

 taceans and other arthropods molt their exoskeletons, 

 grow rapidly, and produce larger exoskeletons. Most 

 reptiles, birds, and mammals molt skin, feathers, and 

 fur, respectively. 



MORPHOLOGY — The appearance, form, and struc- 

 ture of an organism. 



MORPHOMETRICS— The study of comparative mor- 

 phological measurements. 



347 



