Turbellaria
Turbellaria Temporal range: [2]
Possible Ordovician record | |
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A marine species Pseudobiceros bedfordi (Bedford's Flatworm), a member of the Polycladida | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Platyhelminthes |
Class: | Turbellaria Ehrenberg, 1831 |
Subgroups | |
The Turbellaria are one of the traditional sub-divisions of the
The
Description
Traditional classifications divide the
Features common to all Platyhelminthes
As
Features specific to Turbellaria
These have about 4,500 species,
Turbellarians have no
Small aquatic species use the cilia for locomotion, while larger ones use muscular movements of the whole body or of a specialized sole to creep or swim. Some are capable of burrowing, anchoring their rear ends at the bottom of the burrow, then stretching the head up to feed and then pulling it back down for safety. Some terrestrial species throw a thread of mucus which they use as a rope to climb from one leaf to another.[5]
Some Turbelleria have spicular skeletons, giving the appearance of annulations.[8]
Diet and digestion
Most other turbellarians are carnivorous, either preying on small invertebrates or
The intestine is lined by phagocytic cells which capture food particles that have already been partially digested by enzymes in the gut. Digestion is then completed within the phagocytic cells and the nutrients diffuse through the body.
Nervous system
Concentration of nervous tissue in the head region is least marked in the
Most turbellarians have pigment-cup
A few groups – mainly
Most species have ciliated touch-sensor cells scattered over their bodies, especially on tentacles and around the edges. Specialized cells in pits or grooves on the head are probably smell-sensors.[5]
Reproduction
Many turbellarians clone themselves by transverse or longitudinal division, and others, especially acoels, reproduce by budding. The planarian Dugesia is a well-known representative of class Turbellaria.[5]
All turbellarians are simultaneous hermaphrodites, having both female and male reproductive cells, and fertilize eggs internally by copulation.[5] Some of the larger aquatic species mate by penis fencing, a duel in which each tries to impregnate the other, and the loser adopts the female role of developing the eggs.[10]
In turbellarians there are one or more pairs of both
In most species "miniature adults" emerge when the eggs hatch, but a few large species produce plankton-like larvae.[5]
Taxonomy and evolution
Platyhelminthes |
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Detailed morphological analyses of anatomical features in the mid-1980s and molecular phylogenetics analyses since 2000 using different sections of DNA agree that Acoelomorpha, consisting of Acoela (traditionally regarded as very simple turbellarians[5]) and Nemertodermatida (another small group previously classified as "turbellarians"[12]) are the sister group to all other bilaterians, including the rest of the Platyhelminthes.[13][14]
The Platyhelminthes is a clade consisting of two monophyletic groups, Catenulida and Rhabditophora.[11][14]
It has been agreed since 1985 that each of the wholly parasitic platyhelminth groups (
See also
References
- .
- S2CID 134814852.
- ^ Ecology and Classification of North American Freshwater Invertebrates
- ^ ISBN 0-19-551368-1.
- ^ ISBN 0-03-025982-7.
- ISBN 0-632-04917-0. Retrieved 2008-12-21.
- ISBN 0-03-025982-7.
- .
- ^ ISBN 0-03-056747-5.
- PBS. Retrieved 2008-12-21.
- ^ ISBN 0-19-517234-5. Retrieved 2008-12-23.
- S2CID 84015834.
- doi:10.1146/annurev.ecolsys.35.112202.130124. Archived from the original(PDF) on December 16, 2008. Retrieved 2008-12-23.
- ^ .
- S2CID 85917387. Archived from the original(PDF) on 2011-10-06. Retrieved 2008-12-23.
- S2CID 6018712.