Poecilostomatoida
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 Sapphirina darwinii with egg cases
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Poecilostomatoida are plankton-sized crustaceans that are one of two major orders of parasitic copepods previously included in the Cyclopoida.[1][2]
The classification of these copepods has been established on the basis of the structure of the mouth. In poecilostomatoids the mouth is represented by a transverse slit, partially covered by the overhanging labrum which resembles an upper lip. Although there is variability in the form of the mandible among poecilostomatoids, it can be generalized as being falcate (sickle-shaped).[1][2]
The antennules frequently are reduced in size and the antennae modified to terminate in small hooks or claws that are used in attachment to host organisms.[1][2]
As with many crustaceans, larval development is metamorphic with immature forms differing greatly from those of adults. Embryos are carried in paired or single sacs attached to first abdominal somite (as seen in the illustration of the female Sapphirina darwinii above right).[3][4]
Most poecilostomatoid copepods are ectoparasites of saltwater fish or invertebrates (including among the latter mollusks and echinoderms). They usually attach to the external surface of the host, in the throat-mouth cavity, or the gills.[1][2][5][6]
One family of poecilostomatoid copepods, however, have evolved an endoparasitic mode of life and live deep within their hosts' bodies rather than merely attaching themselves to exterior and semi-exterior surface tissue.[1][2]
In addition to typical marine environments, poecilostomatoid copepods may be found in such very particular habitats as anchialine caves and deep sea vents (both hydrothermal vents and cold seeps). Here, many primitive associated copepods belonging to the orders Poecilostomatoida and Siphonostomatoida and have been found.[6]
Finally, representatives of one Poecilostomatoida family have successfully made the transition to freshwater habitats and host animals therein.[1][2]
[edit] List of families
There are over sixty families currently recognized within the group:[7]
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[edit] References
- ^ a b c d e f Humes, A. G. & G. A. Boxshall (1996). A revision of the lichomolgoid complex (Copepoda: Poecilostomatoida), with the recognition of six new families. Journal of Natural History 30: 175–227.
- ^ a b c d e f Martin, J. W. & Davis, G. E. (2001). An Updated Classification of the Recent Crustacea. Natural History Museum of Los Angeles County, 132 pp..
- ^ Lowry, J. K. (1999-10-02). Crustacea, the Higher Taxa: Description, Identification, and Information Retrieval.
- ^ Introduction to Copepods. University of Connecticut.:
The possession of egg sacs is probably not the ancestral condition of the Copepoda since several important groups lack true egg sacs. However, most of the highly transformed parasitic copepods that lack recognisable appendages and external body segmentation belong to the orders Siphonostomatoida, Poecilostomatoida and Cyclopoida all three of which primitively possessed paired egg sacs. The presence of such paired egg sacs constitutes another extremely useful character in identifying secondarily simplified parasites as copepods. This criterion is not infallible because egg sacs are secondarily lost in some highly derived parasitic genera, such as Pectenophilus Nagasawa, an internal parasite of scallops.
- ^ Dojiri, Masahiro. Revision of the Taeniacanthidae (Copepoda–Poecilostomatoida) parasitic on fishes and sea urchins.
- ^ a b Introduction to Copepods. University of Connecticut.
- ^ Poecilostomatoida. Tree of Life Web Project (2002-01-01).
