The life history of Nectobrachia indivisa Fraser, 1920 (Copepoda : Lernaeopodoida) a parasite of the starry flounder Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/pr76f685j

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  • The stages in the life history of the parasitic copepod Nectobrachia indivisa Fraser, 1920, have been described. The adult female lives permanently attached to the gills of the starry flounder, Platichthys stellatus (Pallas, 1811) Girard, 1854. The adult male is a dwarf, which usually lives attached to the genital process of the female. The eggs hatch into free-swimming, but relatively inactive nauplii. They usually molt after 20-40 minutes into vigorous free-swimming copepodid larvae. The copepodid either remains in the gill chamber of the original host or migrates to a new one of the same species. After about three days it attaches itself by means of a chitinous disc and filament to the cuticle of an adult female copepod, usually Nectobrachia indivisa but occasionally Acanthochondria rectangularis (Fraser, 1920) Oakley, 1927, or Lepeophtheirus parvicrurus Fraser, 1920. A withdrawal of the protoplasm from the extremities into the cephalothorax takes place in the copepodid. A new skin forms around the protoplasmic mass and within the old copepodid skin. This marks the advent of the pupal stage. The old copepodid skin may or may not be cast, but the pupa continues to use the original attachment filament. The pupa molts into either an immature female or a nearly mature male. The male soon seeks out an attached female of the same species, matures, and copulates. The post-pupal female remains connected to the pupal case for a period and then attaches permanently to a gill filament of the host by means of an eight-branched bulla. After changing considerably, both in size and morphology, the female becomes sexually mature. Mating occurs and fertile eggs are deposited into the egg sacs. The orientation of embryos in the egg sacs is with head to the inside, opposite to that of Achtheres ambloplitis Kellicott, 1880. Wilson proposed that oxygen supply is the factor in the latter, while ease of hatching may be the advantage of this arrangement for Nectobrachia indivisa. The nauplius differs from all other lernaeopodid nauplii in having mandibles and non-plumose setae. A long club-like process is present on each of the first antennae of the copepodid stage. It may have a sensory function involving taste or smell or both. The attachment of the copepodid appears to require a chitinous substrate. Possible methods of attachment are discussed. The formation of a discrete pupal skin is recognized in this family and the maxillipedal sleeves are described, both for the first time. The latter function as a holdfast for the post-pupal female. The first maxillipeds appear to play an active part in the removal of the bulla from the cephalic region of the post-pupal female. Possible attachment methods are considered and growth after the pupal molt is discussed. There is some evidence in favor of partial molting.
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  • description.provenance : Made available in DSpace on 2013-05-10T16:58:41Z (GMT). No. of bitstreams: 1 WilkesStanleyN1966.pdf: 536772 bytes, checksum: 83d4f21693ca0903fa4eb71fbbb21889 (MD5) Previous issue date: 1965-08-23
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