<Table> <Tr> <Th_colspan="2"> Hydra </Th> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> <Tr> <Td_colspan="2"> Hydra species </Td> </Tr> <Tr> <Th_colspan="2"> Scientific classification </Th> </Tr> <Tr> <Td> Kingdom: </Td> <Td> Animalia </Td> </Tr> <Tr> <Td> Phylum: </Td> <Td> Cnidaria </Td> </Tr> <Tr> <Td> Class: </Td> <Td> Hydrozoa </Td> </Tr> <Tr> <Td> Order: </Td> <Td> Anthoathecata </Td> </Tr> <Tr> <Td> Family: </Td> <Td> Hydridae Dana, 1846 </Td> </Tr> <Tr> <Td> Genus: </Td> <Td> Hydra Linnaeus, 1758 </Td> </Tr> <Tr> <Th_colspan="2"> Species </Th> </Tr> <Tr> <Td_colspan="2"> List (show) <Ul> <Li> * Hydra baikalensis Swarczewsky, 1923 </Li> <Li> * Hydra beijingensis Fan, 2003 </Li> <Li> * Hydra canadensis Rowan, 1930 </Li> <Li> * Hydra cauliculata Hyman, 1938 </Li> <Li> * Hydra circumcincta Schulze, 1914 </Li> <Li> * Hydra daqingensis Fan, 2000 </Li> <Li> * Hydra ethiopiae Hickson, 1930 </Li> <Li> * Hydra hadleyi (Forrest, 1959) </Li> <Li> * Hydra harbinensis Fan & Shi, 2003 </Li> <Li> * Hydra hymanae Hadley & Forrest, 1949 </Li> <Li> * Hydra iheringi Cordero, 1939 </Li> <Li> * Hydra intaba Ewer, 1948 </Li> <Li> * Hydra intermedia De Carvalho Wolle, 1978 </Li> <Li> * Hydra japonica Itô, 1947 </Li> <Li> * Hydra javanica Schulze, 1929 </Li> <Li> * Hydra liriosoma Campbell, 1987 </Li> <Li> * Hydra madagascariensis Campbell, 1999 </Li> <Li> * Hydra magellanica Schulze, 1927 </Li> <Li> * Hydra mariana Cox & Young, 1973 </Li> <Li> * Hydra minima Forrest, 1963 </Li> <Li> * Hydra mohensis Fan & Shi, 1999 </Li> <Li> * Hydra oligactis Pallas, 1766 </Li> <Li> * Hydra oregona Griffin & Peters, 1939 </Li> <Li> * Hydra oxycnida Schulze, 1914 </Li> <Li> * Hydra paludicola Itô, 1947 </Li> <Li> * Hydra paranensis Cernosvitov, 1935 </Li> <Li> * Hydra parva Itô, 1947 </Li> <Li> * Hydra plagiodesmica Dioni, 1968 </Li> <Li> * Hydra polymorpha Chen & Wang, 2008 </Li> <Li> * Hydra robusta (Itô, 1947) </Li> <Li> * Hydra rutgersensis Forrest, 1963 </Li> <Li> * Hydra salmacidis Lang da Silveira et al., 1997 </Li> <Li> * Hydra sinensis Wang et al., 2009 </Li> <Li> * Hydra thomseni Cordero, 1941 </Li> <Li> * Hydra umfula Ewer, 1948 </Li> <Li> * Hydra utahensis Hyman, 1931 </Li> <Li> * Hydra viridissima Pallas, 1766 </Li> <Li> * Hydra vulgaris Pallas, 1766 </Li> <Li> * Hydra zeylandica Burt, 1929 </Li> <Li> * Hydra zhujiangensis Liu & Wang, 2010 </Li> </Ul> </Td> </Tr> </Table> <Tr> <Th_colspan="2"> Hydra </Th> </Tr> <Tr> <Td_colspan="2"> Hydra species </Td> </Tr>

Middle layer in body wall of hydra is known as