venom
336
venom poison secreted by certain animals (e.g., snakes, fish), usually injected by
bite or sting.
venomous marine organisms (or toxic organisms) animals which have the ability to
administer a zootoxin by means of a venom apparatus. This distinguishes
them from organisms which are toxic after they are eaten. Such toxins are
called poisons, although the term poisoning is sometimes used in the general
sense, referring to reactions to both oral poisons and venoms. Some examples of venom apparatuses are nematocysts [e.g., in the Scyphozoa ijellyfish), Cubozoa
(e.g. Chironex fleckeri, the sea wasp), and Siphonophora (e.g. Physalia, the
Portuguese man-of-war)], venom darts (in Gastropoda of the Conus family),
salivary glands and beak of Cephalopoda, spines (e.g., in Synanceia, the stonefish and Trachinus, the we ever) and teeth (in sea snakes). Venoms are mostly
used to paralyze prey, but they may also serve as defense.
vent ---7hydrothermal vent.
ventral situated at, or relatively nearer to, the side of an animal which is normally directed downwards; opposite of dorsal.
Venus Expedition (1836-1839) a French round-the-world expedition under Abel
du Petit-Thouars with Urbain Dortet de Tessan as physicist. Tessan studied
currents, waves, pressure and transparency but became best known for his
temperature measurements for which he used self-registering maximum
and minimum thermometers, protected for pressure. Many observations
gave temperatures well below 4°C; 2.3 °C at 1950 fathoms was the lowest temperature measured. Below 2000 fathoms his thermometers and their cases
were crushed by the pressure. These were the first measurements of temperatures below 4 °C in the deep sea, refuting the theory of d'Urville ( ---7Astrolabe and
Zelee Expedition) and earlier oceanographers that deep-sea waters were uniformly around 4 0c.
Vertebrata (vertebrates) subphylum of the phylum Chordata, constitute less than
5 % of the species of the animal kingdom, characterized by an endoskeleton
that includes a backbone consisting of a series of vertebrae. The vertebrae
develop around the notochord, in most vertebrates only present during the
embryonic development. The Vertebrata contain the classes Agnatha (jawless
fish), Placodermi (fossil armoured fish), Chondrichthyes (cartilaginous fish),
Osteichthyes (bony fish), Amphibia (frogs, toads, salamanders), Reptilia (turtles,
crocodiles, snakes and lizards), Aves (birds) and Mammalia (mammals).
Representatives of all classes, except Amphibia, are found in the sea.
vertical migration one of the most striking aspects of zooplankton behavior is
the diurnal vertical migration exerted by many species of planktonic herbi-
336
venom poison secreted by certain animals (e.g., snakes, fish), usually injected by
bite or sting.
venomous marine organisms (or toxic organisms) animals which have the ability to
administer a zootoxin by means of a venom apparatus. This distinguishes
them from organisms which are toxic after they are eaten. Such toxins are
called poisons, although the term poisoning is sometimes used in the general
sense, referring to reactions to both oral poisons and venoms. Some examples of venom apparatuses are nematocysts [e.g., in the Scyphozoa ijellyfish), Cubozoa
(e.g. Chironex fleckeri, the sea wasp), and Siphonophora (e.g. Physalia, the
Portuguese man-of-war)], venom darts (in Gastropoda of the Conus family),
salivary glands and beak of Cephalopoda, spines (e.g., in Synanceia, the stonefish and Trachinus, the we ever) and teeth (in sea snakes). Venoms are mostly
used to paralyze prey, but they may also serve as defense.
vent ---7hydrothermal vent.
ventral situated at, or relatively nearer to, the side of an animal which is normally directed downwards; opposite of dorsal.
Venus Expedition (1836-1839) a French round-the-world expedition under Abel
du Petit-Thouars with Urbain Dortet de Tessan as physicist. Tessan studied
currents, waves, pressure and transparency but became best known for his
temperature measurements for which he used self-registering maximum
and minimum thermometers, protected for pressure. Many observations
gave temperatures well below 4°C; 2.3 °C at 1950 fathoms was the lowest temperature measured. Below 2000 fathoms his thermometers and their cases
were crushed by the pressure. These were the first measurements of temperatures below 4 °C in the deep sea, refuting the theory of d'Urville ( ---7Astrolabe and
Zelee Expedition) and earlier oceanographers that deep-sea waters were uniformly around 4 0c.
Vertebrata (vertebrates) subphylum of the phylum Chordata, constitute less than
5 % of the species of the animal kingdom, characterized by an endoskeleton
that includes a backbone consisting of a series of vertebrae. The vertebrae
develop around the notochord, in most vertebrates only present during the
embryonic development. The Vertebrata contain the classes Agnatha (jawless
fish), Placodermi (fossil armoured fish), Chondrichthyes (cartilaginous fish),
Osteichthyes (bony fish), Amphibia (frogs, toads, salamanders), Reptilia (turtles,
crocodiles, snakes and lizards), Aves (birds) and Mammalia (mammals).
Representatives of all classes, except Amphibia, are found in the sea.
vertical migration one of the most striking aspects of zooplankton behavior is
the diurnal vertical migration exerted by many species of planktonic herbi-