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Unusual characteristics have led to much controversy regarding the phylogenetic position of Polypodium within metazoans. [2]Polypodium has traditionally been considered a cnidarian because it possesses nematocysts, the stinging structures characteristic of this phylum. [2]
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.
Cnidarians are members of the phylum Cnidaria. Subcategories. This category has the following 13 subcategories, out of 13 total. ... This list may not reflect recent ...
Anatomy of a stalked crinoid. The basic body form of a crinoid is a stem (not present in adult feather stars) and a crown consisting of a cup-like central body known as the theca, and a set of five rays or arms, usually branched and feathery.
Conulariida are an extinct group of medusozoan cnidarians known from fossils spanning from the latest Ediacaran up until the Late Triassic. [1] [2] [3] They are almost exclusively known from their hard external structures (alternatively referred to as a theca, periderm or test), which were pyramidal in shape and made up of numerous lamellae.
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.
Hence ctenophores and cnidarians have traditionally been labelled diploblastic. [18] [20] Both ctenophores and cnidarians have a type of muscle that, in more complex animals, arises from the middle cell layer, [21] and as a result some recent text books classify ctenophores as triploblastic, [22] while others still regard them as diploblastic. [18]
The characteristics of adult echinoderms are the possession of a water vascular system with external tube feet and a stereom endoskeleton. Stereom is a calcareous material consisting of ossicles connected by a mesh of collagen fibres, which is unique to this phylum.