|Abstract or Summary
- 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
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
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.