A gradual increase of stiffness from the surface to the interior is known to prevent crack formation and improve the ability of stiff materials to resist contact damage Suresh et al.Next
It also contains ciliated pits or grooves called nuchal organs.
Perhaps the most unusual occurs in Bonellia viridis , an echiuroid now included within Polychaeta. Notably most Syllidae, Nereididae, and some Eunicidae Palolo worms metamorphose to become night-time swimmers to meet their mates, with timing of swarmings synchronised with the phases of the moon.Next
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They were present in the middle Cambrian in the Burgess Shale in taxa resembling, in certain respects, recent canalipalpates. Whether such hermaphrodites are self-fertile or not is species-specific and often has not been determined. The body also contains greenish "chloragogen" tissue, similar to that found in , which appears to function in metabolism, in a similar fashion to that of the vertebrate.Next
Polychaeta PowerPoint PPT Presentations Because the groundplan of the Ecdysozoa becomes highly modified with the gradual development of a chitinous exoskeleton, most polychaetoid characters are difficult to recognize in arthropods and their relatives.
Food is drawn inward by the sucking action of their muscular pharynx. The posterior segments make up the epitokal region, consisting of segments packed with gametes.Next
First, in calcareous tube-dwelling serpulid polychaetes, one of a bilateral pair of anterior gill filaments transforms into an operculum that plugs the tube when the animal withdraws Zeleny, 1905.
Their major features match the polychaetes well, and they are included here as a single family of polychaetes, Siboglinidae. Polychaetes play an important role in turning over bottom sediments in the sea. In these cases, the adult soon dies.Next
GAS EXCHANGE AND CIRCULATION Respiration Respiratory gases diffuse through the body wall.
The upshot of the scattered records shows that most major taxa of polychaetes must have been present by the Ordovician and some clades may be even older than that.
Polychaetes are extremely abundant in some areas.
Eyes: Polychaetes have various sensory structures. PM, plasma membrane; cc, cortical cytomembranes; m, mitochondrion. They have more than 5.Next
Fig: a Nervous System of a Polychaete.