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Teuthidodrilus (also known as the squidworm), is a genus of marine polychaete worms first described by marine biologists from the Scripps Institution of Oceanography in November 2010. This unique animal is currently believed to represent a "transitional organism", with physical and behavioral characteristics of both benthic (seabed-dwelling) and pelagic (free-swimming) organisms. Teuthidodrilus samae is currently the only described species of this genus. Teuthidodrilus is closely related to the recently discovered Swima genus, another pelagic cirratuliform worm of the deep ocean.
Teuthidodrilus is one of seven recently discovered deep-sea, pelagic cirratuliforms. The first specimen was observed in the Celebes Sea in October 2007. A second specimen was discovered in a nearby area by a group of marine biologists from the Scripps Institution of Oceanography in November 2010. Using a remotely operated underwater vehicle during exploration of the deep water column of the western Celebes Sea, the team found the animals at a depth of 2.8 kilometres (1.7 mi). The Celebes Sea is a deep oceanic basin with a maximum depth of 20,300 feet (6,200 metres). It is part of the Coral Triangle, an area known for its high biodiversity.
Classification and phylogeny
Teuthidodrilus is thought to be a previously unobserved genus which may represent a transition between the benthos and the pelagic organisms. Teuthidodrilus is one of seven newly discovered species of swimming cirratuliforms. These seven species have been assigned to four new genera, forming a new phylogenetic clade within the Acrocirridae family. Following is a brief description of the cladistics and taxonomic classification of Teuthidodrilus:
- Phylogenetic analysis of five of its genes has revealed that the Teuthidodrilus genus belongs to the Acrocirridae family.
- the Acrocirridae family is a member of the Terebellida suborder of the Canalipalpata order, also known as bristle-footed annelids or fan-head worms.
- the Canalipalpata order belongs to the Polychaeta class, also known as bristle worms. There are more than 10,000 described species of polychaetes; they can be found in nearly every marine environment. Some species live in the coldest ocean waters of the abyssal plain, while others can be found in the extremely hot waters adjacent to hydrothermal vents. Polychaetes occur throughout the World Ocean at all depths, from forms that live as plankton near the surface, to a 2–3 cm specimen (still unclassified) observed by the robotic ocean probe Nereus at the bottom of the Challenger Deep, the deepest spot in the Earth's oceans.
- the Polychaete class belongs to the Annelid phylum, also known as also called ringed worms. There are over 17,000 living annelid species, ranging in size from microscopic to the Australian giant Gippsland earthworm, which can grow up to 3 metres (9.8 ft) long.
Anatomy and physiology
Teuthidodrilus specimens observed and collected as of 2010 have measured up to 9.4 centimetres (3.7 inches) in length. These animals are notable for the unusual tentacular appendages (referred to as "notochaetae") that protrude from its prostomium (anterior segment, or head). Ten of these tentacles as long or longer than its body protrude from the head, along with six pairs of free-standing, oppositely branched nuchal organs that allow the animal to taste and smell underwater. It is the notochaetae and the nuchal organs which primarily distinguish Teuthidodrilus from other polychaetes.
Teuthidodrilus does not appear to be a predator, feeding instead on bits of so-called "marine snow," a mix of sinking microscopic plants and animals, fecal material and cast-off mucus. Swimming upright, it navigates by moving two body-length rows of thin, paddle-shaped protrusions that cascade like dominoes.
Geographic distribution and habitat
Squidworms live about 100 to 200 metres above the ocean floor.
Teuthidodrilus worms belong to a morphologically diverse pelagic clade within the Acrocirridae family of polychaetes. The acrocirrids are primarily benthic. Pelagic animals within primarily benthic families are of particular interest in evolutionary biology, because their adaptations to life in the water column inform us of the evolutionary possibilities and constraints within the clade and indirectly of the selective pressures at work in this unfamiliar habitat.
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