221
outwelling
Osteichthyes (syn. Teleostei, bony fish) far the largest class of the Vertebrata, containing most of the important foodfish from freshwater and the sea. These
fish (~Pisces) are distinguished from the Chondrichthyes by their ossified or
bony skeleton. Particularly the skeleton of the head contains many bony elements fused into a skull with well-developed tooth-bearing jaws. There is a
single gill opening on both sides, covered by a complex of bones forming the
operculum or gill cover. The skin is mostly covered by partly embedded scales,
which are thought to have formed during evolution when fish spread out into
freshwater. A gas bladder is present which besides providing for the buoyancy of
the fish, is sometimes used as a sort of respiratory organ, or a resonance box
for the auditory organs. Bony fish have external fertilization and are, with a
few exceptions, oviparous. This class is divided into three subclasses: the Sarcopterygii with the lungfish and the lobe fins, which represent the famous
coelacanth (Latirneria), the Brachiopterygii with the bichirs (Polypterus),
and the Actinopterygii or higher bony fish. This latter subclass with over
20000 known species is the largest and most diverse group of vertebrate animals. They are a very important source of protein for mankind and millions
of tons are harvested each year. Economically significant species are the herring (Clupea), salmon (Salrno), cod (Gadus), perch such as scad (Trachurus)
and mackerel (Scornber), and finally the flatfish (Pleuronectes, Solea).
Ostracoda (mussel-shrimps) class of the subphylum Crustacea (phylum Arthropoda). Small (a few mm) crustaceans, with the body completely enclosed by a
bivalved, often calcified carapace. This carapace superficially looks like the
miniature shell of a common mussel (~Bivalvia), but it has no growth lines,
as it is shed and renewed at each molt. The animals have only five to seven
appendages. They occur in freshwater and all marine habitats, are benthic
crawlers or burrowers, some swim and some are holoplanktonic. The food
varies, depending on the species, from detritus and plant material to even
small fish. There is also a wide variety of fossil species, restricted to discrete
depth ranges, which makes them useful depth indicators, while their rapidly evolving lineages make them useful as stratigraphic markers (i.e., tools
for correlation). ~biostratigraphy. (Figure see p. 222)
otolith ear-stone of fish, which generally shows distinct daily and annual
growth rings, which are a measure for the age of the individual. Used as statoliths (~statocysts). The growth rings can be used in age determination of the
fish. Otoliths are species specific, and are usually the only parts of the fish
that fossilise.
otter trawl ~trawl.
outwelling a process of export of nutrients and organic matter from an estuary
into the ocean, enriching (fertilizing) the ocean adjacent to the estuary.
outwelling
Osteichthyes (syn. Teleostei, bony fish) far the largest class of the Vertebrata, containing most of the important foodfish from freshwater and the sea. These
fish (~Pisces) are distinguished from the Chondrichthyes by their ossified or
bony skeleton. Particularly the skeleton of the head contains many bony elements fused into a skull with well-developed tooth-bearing jaws. There is a
single gill opening on both sides, covered by a complex of bones forming the
operculum or gill cover. The skin is mostly covered by partly embedded scales,
which are thought to have formed during evolution when fish spread out into
freshwater. A gas bladder is present which besides providing for the buoyancy of
the fish, is sometimes used as a sort of respiratory organ, or a resonance box
for the auditory organs. Bony fish have external fertilization and are, with a
few exceptions, oviparous. This class is divided into three subclasses: the Sarcopterygii with the lungfish and the lobe fins, which represent the famous
coelacanth (Latirneria), the Brachiopterygii with the bichirs (Polypterus),
and the Actinopterygii or higher bony fish. This latter subclass with over
20000 known species is the largest and most diverse group of vertebrate animals. They are a very important source of protein for mankind and millions
of tons are harvested each year. Economically significant species are the herring (Clupea), salmon (Salrno), cod (Gadus), perch such as scad (Trachurus)
and mackerel (Scornber), and finally the flatfish (Pleuronectes, Solea).
Ostracoda (mussel-shrimps) class of the subphylum Crustacea (phylum Arthropoda). Small (a few mm) crustaceans, with the body completely enclosed by a
bivalved, often calcified carapace. This carapace superficially looks like the
miniature shell of a common mussel (~Bivalvia), but it has no growth lines,
as it is shed and renewed at each molt. The animals have only five to seven
appendages. They occur in freshwater and all marine habitats, are benthic
crawlers or burrowers, some swim and some are holoplanktonic. The food
varies, depending on the species, from detritus and plant material to even
small fish. There is also a wide variety of fossil species, restricted to discrete
depth ranges, which makes them useful depth indicators, while their rapidly evolving lineages make them useful as stratigraphic markers (i.e., tools
for correlation). ~biostratigraphy. (Figure see p. 222)
otolith ear-stone of fish, which generally shows distinct daily and annual
growth rings, which are a measure for the age of the individual. Used as statoliths (~statocysts). The growth rings can be used in age determination of the
fish. Otoliths are species specific, and are usually the only parts of the fish
that fossilise.
otter trawl ~trawl.
outwelling a process of export of nutrients and organic matter from an estuary
into the ocean, enriching (fertilizing) the ocean adjacent to the estuary.