Nematomorpha
206
which because of their cuticula and high internal turgor-pressure often look
like a flexible needle. The mouth is at the front and the digestive tract ends
sub terminally in an anus, so all animals have a tail. Sensory organs like setae
or papillae can be spread over the body, but are mostly restricted to certain
parts, especially the head. The head characteristically also has two lateral
chemoreceptors, the amphids. Most live interstitially in the bottom, or are parasitic (especially on plants). They are very common all over the world especially in moisty areas. In marine sediments they form the majority of the
meiobenthos, and can reach densities up to several tens of millions per square
meter. Locomotion is by wriggling. They eat small dead or living animals,
like Bacteria, Bacillariophyta (diatoms), Foraminifera and small Metazoa. The sexes
are generally separated, sometimes females attract males with a pheromone,
and after copulation the eggs are deposited and hatch directly into small
look-alike adults. There are hermaphroditic forms; parthenogenesis occurs as well.
Nematomorpha (gordian or horsehair worms) phylum of long and very slender
worms, that are parasitic as juveniles in Arthropoda, and have a short free-living sexual mature stage. In neither stage is there a functional digestive tract.
In the sea there is only one genus, Nectonema. It is living in the body cavities of decapod crustaceans, and the adult is mostly pelagic.
Nemertea ~Nemertina.
Nemertina (ribbon worms) phylum of mostly marine, unsegmented worms, also
called Nemertea, Nemertini or Rhynchocoela. Elongated and often flattened predatory worms, with a ciliated skin that can produce a lot of mucus. Typical
of the phylum is a well-developed proboscis, in front of the mouth, with which
they grab or stab their invertebrate prey. The digestive tract ends in an anus.
The animals are very contractile, and generally live in the seabed, or under
stones or seaweed. Few species are terrestrial, parasitic, commensal or live in
freshwater. Especially the larger species have the tendency to produce lots of
mucus, and to fragmentize themselves when disturbed.
Nemertini ~Nemertina.
Neogene the name given to the Miocene and Pliocene periods of the Tertiary
grouped together. ~geological time scale.
nepheloid layer water layer on the shelf or in the deep ocean, usually near the
bottom, where suspended matter concentrations are relatively high. On the
shelf such a layer may be less than 10 to more than 20 m thick; in the deep
sea its thickness may vary from 200 m to 1000 m.
206
which because of their cuticula and high internal turgor-pressure often look
like a flexible needle. The mouth is at the front and the digestive tract ends
sub terminally in an anus, so all animals have a tail. Sensory organs like setae
or papillae can be spread over the body, but are mostly restricted to certain
parts, especially the head. The head characteristically also has two lateral
chemoreceptors, the amphids. Most live interstitially in the bottom, or are parasitic (especially on plants). They are very common all over the world especially in moisty areas. In marine sediments they form the majority of the
meiobenthos, and can reach densities up to several tens of millions per square
meter. Locomotion is by wriggling. They eat small dead or living animals,
like Bacteria, Bacillariophyta (diatoms), Foraminifera and small Metazoa. The sexes
are generally separated, sometimes females attract males with a pheromone,
and after copulation the eggs are deposited and hatch directly into small
look-alike adults. There are hermaphroditic forms; parthenogenesis occurs as well.
Nematomorpha (gordian or horsehair worms) phylum of long and very slender
worms, that are parasitic as juveniles in Arthropoda, and have a short free-living sexual mature stage. In neither stage is there a functional digestive tract.
In the sea there is only one genus, Nectonema. It is living in the body cavities of decapod crustaceans, and the adult is mostly pelagic.
Nemertea ~Nemertina.
Nemertina (ribbon worms) phylum of mostly marine, unsegmented worms, also
called Nemertea, Nemertini or Rhynchocoela. Elongated and often flattened predatory worms, with a ciliated skin that can produce a lot of mucus. Typical
of the phylum is a well-developed proboscis, in front of the mouth, with which
they grab or stab their invertebrate prey. The digestive tract ends in an anus.
The animals are very contractile, and generally live in the seabed, or under
stones or seaweed. Few species are terrestrial, parasitic, commensal or live in
freshwater. Especially the larger species have the tendency to produce lots of
mucus, and to fragmentize themselves when disturbed.
Nemertini ~Nemertina.
Neogene the name given to the Miocene and Pliocene periods of the Tertiary
grouped together. ~geological time scale.
nepheloid layer water layer on the shelf or in the deep ocean, usually near the
bottom, where suspended matter concentrations are relatively high. On the
shelf such a layer may be less than 10 to more than 20 m thick; in the deep
sea its thickness may vary from 200 m to 1000 m.