Misostomida ( lat. Myzostomida ) - class of annelids ( Annelida ). The concepts of kinship between mizostomid and other invertebrates have undergone significant changes in recent years [1] . The class has about 170 species, combined into 12 genera [1] . All representatives are obligate ectocommensals , ecto-or endo parasites of echinoderms . In the seas of Russia, there are 6 known species inhabiting the Barents , Kara , Bering , Okhotsk and Japanese seas [2] .
| Misostomid | |||||||||||||||||
 Myzostoma fuscomaculatum on sea ββlily ( South Africa ) | |||||||||||||||||
| Scientific classification | |||||||||||||||||
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| International Scientific Name | |||||||||||||||||
Myzostomida Benham , 1896 | |||||||||||||||||
Content
Build
The body of mizostomid is highly flattened and has an oval or round shape. The length of adult individuals in different species varies from 0.5 mm to 1.3 cm [2] . In the arrangement of the external organs, there is a distinct metameric symmetry . Numerous antennae, often reaching considerable length, depart from the sides.
On the ventral side, there are 5 pairs of mobile outgrowths ( parapodia ) bearing one hook-like chitinous seta. Traditionally, the parapodia of mizostomid is considered homologous to the parapodia of polychaete worms , although studies of the larval development of myostomid revealed a fundamentally different sequence of their establishment [3] . Also on the ventral side of the body there are 4 pairs of lateral organs , supposedly performing the functions of the sense organs [1] .
The digestive system begins with the buccal cavity , followed by a muscular pharynx . Numerous outgrowths ( diverticula ), which function as a distribution system, depart from the midgut [1] . The intestine ends up with a cloaca , where the channels of the excretory system, consisting of one or more pairs of metanephridias, open. Not far from the vent of the cloaca, the oviduct opens [4] .
The brain is poorly developed, eyes are missing [2] . Specialized respiratory and circulatory systems are absent.
Lifestyle
Most of the species are ectocommensals of lilies [5] . They lead a mobile lifestyle on the surface of the host body, holding onto the surface with the help of hook-shaped bristles [1] . A number of representatives turned to parasitism and settled in the integuments, the digestive tract, the body cavity or the sex glands of sea ββlilies , starfish , and ofiur [5] . Parasites of coral lilies cause characteristic tissue growths, called cysts [2] or galls [5] .
Reproduction and development
The misostomids are protandric hermaphrodites : in young individuals, the male sex glands first mature and only after a while - the female. When mating, a functional male implants spermatofors into the tissues of a functional female, after which the spermatozoids contained in it migrate to mature eggs independently and merge with them. A planktonic larva similar to the trochophore of polychaetes leaves the fertilized egg [1] .
Notes
- β 1 2 3 4 5 6 Bleidorn C., Eeckhaut I., Podsiadlowski L., Schult N., McHugh D., Halanych KM, Milinkovitch MC, Tiedemann R. (2007). Mitochondrial genome; Molecular Biology and Evolution, 2007, vol. 24 (8), pp. 1690-1701. DOI : 10.1093 / molbev / msm086 Text (eng.)
- β 1 2 3 4 Mizostomida / P. V. Ushakov // MΓΆziya - Morshansk. - M .: Soviet Encyclopedia, 1974. - ( Great Soviet Encyclopedia : [in 30 t.] / Ch. Ed. AM Prokhorov ; 1969-1978, t. 16).
- β JΓ€gersten G. (1940). Zur Kenntnis der Morphologie, Entwicklung und Taxonomie der Myzostomida. Nova Acta Regiae Societatis Scientiarum Uppsaliensis, Bd. 11, pp. 1β84. (him)
- Ruppert E.E., Fox R.S., Barnes R.D., Invertebrate Zoology: Functional and Evolutionary Aspects. T. 2: Lower coelomic animals. - M .: Publishing Center "Academy", 2008. - 448 p.
- β 1 2 3 Eeckhaut I., McHugh D., Mardulyn P., Tiedemann R., Monteyne D., Jangoux M., Milinkovitch MC (2000). Myzostomida: a link between trochozoans and flatworms? Proceedings of the Royal Society of London, 2000, vol. 267, pp. 1383-1392. Text (Eng.)
Links
- L. von Graf (1884). Report on mizostomida collected by the corvette Challenger (eng.) - information on individual representatives, drawings.
- Photos of misostomid: on the sea lily arm , dorsal side , ventral side . The author is Greg Rouse.