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Hydra has two main body layers, which makes it "diploblastic". The layers are separated by mesoglea, a gel-like substance. The outer layer is the epidermis, and the inner layer is called the gastrodermis, because it lines the stomach. The cells making up these two body layers are relatively simple.
Siphonophorae (from Greek siphōn 'tube' + pherein 'to bear' [2]) is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria.According to the World Register of Marine Species, the order contains 175 species described thus far.
Pacific sea nettles, Chrysaora fuscescens. Cnidaria (/ n ɪ ˈ d ɛər i ə, n aɪ-/ nih-DAIR-ee-ə, NY-) [4] is a phylum under kingdom Animalia containing over 11,000 species [5] of aquatic invertebrates found both in fresh water and marine environments (predominantly the latter), including jellyfish, hydroids, sea anemones, corals and some of the smallest marine parasites.
Main axis is a single enlarged and elongated polyp. Has several types of specialist polyp. Azooxanthellate. [10] Worldwide, from lower tidal to 6,000 m (20,000 ft) [12] Ceriantharia: Penicillaria Tube-dwelling anemones: Arachnanthus sarsi: Solitary individuals with two rings of tentacles living in fibrous tubes in soft sediment.
Hydra and Craspedacusta sowerbii are distantly related and are not closely related to Polypodium. Also, the obligate parasite Myxobolus cerebralis lives in freshwater. Thus, it appears that in the evolution of cnidarians, invasion of freshwater habitats has happened at least three separate times.
Hydra viridissima is a species of cnidarian which is commonly found in still or slow-moving freshwater [2] in the Northern temperate zone. Hydra viridissima is commonly called green hydra due to its coloration, which is due to the symbiotic green algae Chlorella vulgaris which live within its body. [ 3 ]
Apart from Dickinsonia, the earliest widely accepted animal fossils are the rather modern-looking cnidarians (the group that includes jellyfish, sea anemones and Hydra), possibly from around 7] The Ediacara biota, which flourished for the last 40 million years before the start of the Cambrian, [8] were the first animals more than a very few ...
The classical example of morphallaxis is that of the Cnidarian hydra, where when the animal is severed in two (by actively cutting it with, for example, a surgical knife) the remaining severed sections form two fully functional and independent hydra. The notable feature of morphallaxis is that a large majority of regenerated tissue comes from ...