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Pharyngeal Slit
Pharyngeal slits are filter-feeding organs found among deuterostomes. Pharyngeal slits are repeated openings that appear along the pharynx caudal to the mouth. With this position, they allow for the movement of water in the mouth and out the pharyngeal slits. It is postulated that this is how pharyngeal slits first assisted in filter-feeding, and later, with the addition of gills along their walls, aided in respiration of aquatic chordates. These repeated segments are controlled by similar developmental mechanisms. Some hemichordate species can have as many as 200 gill slits. Pharyngeal clefts resembling gill slits are transiently present during the embryonic stages of tetrapod development. The presence of pharyngeal arches and clefts in the neck of the developing human embryo famously led Ernst Haeckel to postulate that "ontogeny recapitulates phylogeny"; this hypothesis, while false, contains elements of truth, as explored by Stephen Jay Gould in ''Ontogeny and Phylogeny''.. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gill Slits
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of Chondrichthyes, cartilaginous fish such as sharks and Batoidea, rays, as well as deep-branching vertebrates such as Lamprey, lampreys. In contrast, bony fishes have a single outer bony gill covering called an Operculum (fish), operculum. Most sharks and rays have five pairs of gill slits, but a few species have 6 or 7 pairs. Shark gill slits lie in a row behind the head. The anterior edge of a gill slit is motile, moving outward to allow water to exit, but closing to prevent reverse flow. A modified slit, called a Spiracle (vertebrates), spiracle, lies just behind the eye, which assists the shark with taking in water during Aquatic respiration, respiration and plays a major role in bottom–dwelling sharks. Spiracles are reduced or missing in active pelagic sharks. While the shark is moving, water passes through the mouth and over the gills in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
