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Invertebrates also have a pharynx. Invertebrates with a pharynx include the tardigrades, [12] annelids and arthropods, [13] and the priapulids (which have an eversible pharynx). [14] The "pharynx" of the nematode worm is a muscular food pump in the head, triangular in cross-section, that grinds food and transports it directly to the intestines ...
Their pharynx, when everted, clearly consists of two portions, with a pair of strong jaws on the distal portion and usually with conical teeth on one or more areas of both portions. Most genera have no gills (if present, they are usually branched and arise on mid-anterior segments of body).
Thus each worm becomes the genetic father of some of their offspring (due to its own sperm transferred to other earthworm) and the genetic mother (offsprings from its own egg cells) of the rest. As the worm slips out of the ring, the ends of the cocoon seal to form a vaguely onion-shaped incubator in which the embryonic worms develop. Hence ...
The presence of gill slits (in blue) in an acorn worm (left) and a tunicate (right). 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.
Once in the trachea, the worms are coughed up into the pharynx and then swallowed again, after which they pass through the stomach and into the small intestine, where they mature into adult worms. [ 5 ] [ 7 ] The adult worms begin producing fertilized eggs within 60–65 days of being swallowed; [ 7 ] females produce as many as 200,000 eggs per ...
This allows for parasitic worms to attach to their host by penetrating the host’s tissue with spines lining the acetabulum organ. In trematodes, the oral sucker is linked to the pharynx via a canal composed of meridional, equatorial, and radial muscle fibers. [13] Together, the mouth, pharynx, and esophagus form the foregut in Trematodes. [14]
Most other turbellarians have a pharynx that is eversible (can be extended by being turned inside-out), and the mouths of different species can be anywhere along the underside. [5] The freshwater species Microstomum caudatum can open its mouth almost as wide as its body is long, to swallow prey about as large as itself. [13]
The majority of such amputated worms (95%) did not do so, however. An amputated worm regenerated into a double-head creature after spending five weeks aboard the International Space Station (ISS) – though regeneration of amputated worms as double-headed heteromorphosis is not a rare phenomenon unique to a microgravity environment. [36]