User:Erinea/Ophryotrocha

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Ophryotrocha comprises forty extant species of polychaete worms with more thought to exist in both shallow and deep waters. Polychaetes of this genus thrive in nutrient-rich environments and can often be found in polluted marine areas that are often sites of human activity. Ophryotrocha's durability allows them to exist in a myriad of stressful environments. Found in the oceans surrounding Europe, Asia, the Mediterranean, and beyond, they can survive in low-oxygen environments and are known to be sulfide tolerant, allowing this genus to live in areas most species cannot. Most worms are between 1 and 5 mm in length, but some deep sea species have been documented to be much larger, ranging from 10 and 25mm. Ophryotrocha is often used as a scientific test species due to their high fecundity, stress tolerance, and myriad of sexual systems found within the genus.

All polychaetes of this genus are laid in batches of roughly 100 eggs and the majority of species start out in a free-moving larval stage as protandrous hermaphrodites. During the protandrist stage of adolescence, small males will start producing sperm when the body length is still small but will continue to stay male if females are present in an effort to avoid the energetic costs of producing oocytes. As this genus continues to grow they develop into tube-building sessile adults. Although no study has documented their entire life process, all Ophryotrocha are documented to breed and die after the dispersal of offspring with parental care given to eggs by one or both sexes resting on the egg cocoon. Parental care is thought to act as a mode for cleaning the cocoon and is documented in all studied species within the genus.

Sexual Systems
The many species of polychaete worms within the genus Ophryotrocha exhibit a variety of sexual systems. Distinct species demonstrate different systems, with simultaneous hermaphroditism, gonochorism, and sequential hermaphroditism all documented. The ancestral state of this genus of worms is known to be simultaneous hermaphroditism. Generally, the simultaneous hermaphroditic species are protandrous as adolescents and mate in pairs. The formation of pairs is decided by a long courtship process where partners are linked together in a pseudocopulation. In simultaneous hermaphrodites, each adult has a pair of gonads that produce gametes which are emitted into the water column where external fertilization occurs. After courtship, both simultaneous hermaphroditic individuals repeat the process of egg-laying and fertilizing (known as egg trading to avoid sexual conflict between the two simultaneous hermaphrodites. As with many hermaphroditic species, Ophryotrocha polychaetes are thought to have evolved simultaneous hermaphroditism as an ancestral state because of lack of mate access to allow sexually viable individuals to produce offspring without sex barriers blocking reproduction opportunities as this genus cannot self-fertilize..