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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.
Only one species is found in the genus which also gave name to the family. The name literally translates as "the fish louse with many children". The parasite can infect most freshwater fish species and, in contrast to many other parasites, shows low host specificity.
Polypodium was long considered a unique intracellular parasite among cnidarians. [6] [7] Its hosts include 14 species of Acipenser, 2 species of Huso, Polyodon spathula [6] and Scaphirhynchus platorynchus. [2] Polypodium hydriforme is an endocellular parasite with an unusual life cycle, a peculiar morphology, and high rates of DNA evolution.
Gland cells in the basal disc secrete a sticky fluid that accounts for its adhesive properties. At the free end of the body is a mouth opening surrounded by one to twelve thin, mobile tentacles. Each tentacle, or cnida (plural: cnidae), is clothed with highly specialised stinging cells called cnidocytes.
Cell division by binary fission is rare, and cells divide instead via endogeny. [15] In 2020, the myxozoan Henneguya salminicola was found to lack a mitochondrial genome, and thus be incapable of aerobic respiration; it was the first animal to be positively identified as such. Its actual metabolism is currently unknown.
Isopod fish parasites are mostly external and feed on blood. The larvae of the Gnathiidae family and adult cymothoidids have piercing and sucking mouthparts and clawed limbs adapted for clinging onto their hosts. [20] [21] Cymothoa exigua is a parasite of various marine fish. It causes the tongue of the fish to atrophy and takes its place in ...
Larval anisakids are common parasites of marine and anadromous fish (e.g. salmon, sardine), and can also be found in squid and cuttlefish. In contrast, they are absent from fish in waters of low salinity, due to the physiological requirements of krill , which are involved in the completion of the worm's life cycle.
Hydrozoa (hydrozoans; from Ancient Greek ὕδωρ (húdōr) 'water' and ζῷον (zôion) 'animal') is a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water.