Cephalopod
| Cephalopods | ||||||
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 Juvenile cephalopod from plankton Antarctica | ||||||
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Sepiida Sepiolida Spirulida Teuthida Octopoda Vampyromorphida Nautilida |
Cephalopods are characterized by bilateral body symmetry, a prominent head, and a modification of the mollusc foot into the form of arms or tentacles. The class contains two subclasses. In the Coleoidea, the mollusc shell has been internalized or is absent; this subclass includes the octopuses, squids, and cuttlefish. In the Nautiloidea the shell remains; this subclass includes the nautilus. There are around 786 distinct living species of Cephalopods. Two important extinct subclasses are Ammonoidea, the ammonites and Belemnoidea, the belemnites.
Cephalopods are found in all the oceans of the world and at all depths. They are regarded as the most intelligent of the invertebrates and have well developed senses. They have special skin cells call chromatophores that change color and are used for communication and camouflage.
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2 Classification 3 External links |
Evolution
The class developed during the late Cambrian and were during the Paleozoic and Mesozoic dominant and diverse marine life forms. Early cephalopods were at the top of the food chain. The ancient (cohort Belemnoidea) and modern Coleoidea (cohort Neocoleoidea) diverged from the external shelled Nautiloidea around 425 million years ago. Unlike most modern cephalopods, ancient varieties had protective shells. These shells at first were conical but later developed into curved nautiloid shapes seen in modern nautilus species. Internal shells still exist in many non-shelled living cephalopod groups but most truly shelled cephalopods, such as the ammonites, became extinct at the end of the Cretaceous.
Classification
The classification as listed here (and on other cephalopod articles) follows primarily from Current Classification of Recent Cephalopoda (May 2001). Other classifications [1] [1] differ, primarily in how the various decapod orders are related, and whether they should be orders or families.
- CLASS CEPHALOPODA
- Subclass Nautiloidea: nautilus
- Order Nautilida
- (Order Bacritina): extinct ancestors of ammonites and coleoids
- (Subclass Ammonoidea): extinct ammonites
- Subclass Coleoidea
- (Cohort Belemnoidea): extinct belemnites
- Cohort Neocoleoidea
- Subclass Nautiloidea: nautilus