Agnatha - Lamprey, Hagfish | Wildlife Journal Junior
They are descendants of extinct armored agnathans that were once widespread and were the precursors also of the . Most are parasitic. Agnatha (Greek, "no jaws") is a superclass of jawless fish in the phylum Chordata , subphylum . While today enough fossil diversity is known to make a close relationship among the "ostracoderms" unlikely, this has muddied the issue of the . the extant agnathans (cyclostomes) are discussed in relation to their adaptations In some parasitic species juveniles are capable of marine osmoregulation.
Most agnathans have a skeleton made of cartilage and seven or more paired gill pockets. They have a light sensitive pineal eye. A pineal eye is a third eye in front of the pineal gland. Fertilization of eggs takes place outside the body.
Agnatha - New World Encyclopedia
The lamprey looks like an eel, but it has a jawless sucking mouth that it attaches to a fish. It is a parasite and sucks tissue and fluids out of the fish it is attached to. The lamprey's mouth has a ring of cartilage that supports it and rows of horny teeth that it uses to latch on to a fish.
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Lampreys are found in temperate rivers and coastal seas and can range in size from 5 to 40 inches. Lampreys begin their lives as freshwater larvae.
In the larval stage, lamprey usually are found on muddy river and lake bottoms where they filter feed on microorganisms. The larval stage can last as long as seven years! At the end of the larval state, the lamprey changes into an eel-like creature that swims and usually attaches itself to a fish.
Other recent reviews have focused on the developmental biology of lampreys, and their use in a broad variety of experimental contexts Martin et al. In this review, we particularly focus on the ways in which lamprey data have facilitated understanding of the evolution of neural crest.
Lamprey: a model for vertebrate evolutionary research
Lamprey phylogeny, anatomy, and fossil record Lampreys and hagfish are jawless fishes with anatomic characters that unambiguously suggest a relatively close relationship with jawless vertebrates. The precise phylogenetic position of hagfish and lampreys relative to the jawed vertebrates has been a difficult issue to resolve, with many early phylogenetic analyses of morphological datasets suggesting that lampreys and jawed vertebrates are sister groups to the exclusion of hagfishbut molecular phylogenetic data have supported a close relationship between hagfish and lampreys, suggesting they comprise a monophyletic group Kuraku et al.
This has remained a contentious issue, but analyses of microRNA sequences, reexamination of morphological datasets, and recent morphological analyses of hagfish De Beer, ; Heimberg et al.
Of the two cyclostome groups, hagfish are more difficult to acquire, but have recently begun receiving significant attention Gess et al.
Lampreys are by far more accessible, and have been the subject of more developmental analyses.
The phylogenetic position of lampreys makes them particularly useful for comparisons with jawed vertebrates, as traits held in common between these groups are possibly homologous by descent. Development in both groups probably is external. There is no known parental care. Not much is known about the hagfish reproductive process.
Agnathans | piliciauskas.info
It is believed that hagfish only have 30 eggs over a lifetime. There is very little of the larval stage that characterizes the lamprey.10 Mind Controlling Parasites
Lamprey are only able to reproduce once. After external fertilization, the lamprey's cloacas remain open, allowing a fungus to enter their intestines, killing them.
Lampreys reproduce in freshwater riverbeds, working in pairs to build a nest and burying their eggs about an inch beneath the sediment.