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All free-living species exhibit a distinct and separate mouth and anus, and in all species, food must be moved through the digestive tract by muscular activity rather than cilia activity since the lumen of the fore gut and hind gut is lined with cuticle. Digestion is generally extracellular.
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.
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.
Sea pens are marine cnidarians belonging to the order Pennatulacea, which are colony-forming benthic filter feeders within the class Octocorallia (subphylum Anthozoa).There are 14 families within the order and 35 extant genera; it is estimated that of 450 described species, around 200 are valid.
Like cnidarians, ctenophores have two main layers of cells that sandwich a middle layer of jelly-like material, which is called the mesoglea in cnidarians and ctenophores; more complex animals have three main cell layers and no intermediate jelly-like layer. Hence ctenophores and cnidarians have traditionally been labelled diploblastic.
Anthozoa is a class of marine invertebrates which includes sessile cnidarians such as the sea anemones, stony corals, soft corals and sea pens.Adult anthozoans are almost all attached to the seabed, while their larvae can disperse as planktons.
Although unspecified species of box jellyfish have been called in newspapers "the world's most venomous creature" [40] and the deadliest creature in the sea, [41] only a few species in the class have been confirmed to be involved in human deaths; some species are not harmful to humans, possibly delivering a sting that is no more than painful. [9]
Our Planet is a British nature documentary series made for Netflix.The series is narrated by David Attenborough and produced by Silverback Films, led by Alastair Fothergill and Keith Scholey, who also created BBC documentary series Planet Earth, Frozen Planet and The Blue Planet, in collaboration with the conservation charity World Wildlife Fund (WWF).