Biology Reference
In-Depth Information
Figure 10.3. Larva of Lobatostoma manteri. Note the large posterior sucker and the
muscular anterior pseudosucker, lack of microfila, ciliary tufts, and eyes. Redrawn
and modified from Rohde (
1973
).
blochi,ontheGreatBarrierReef,Australia. Eggs containing fully devel-
oped larvae are laid. Larvae are about 150-200 mm long and lack the
layer of microfila found in Multicotyle (Figure
10.3
). They have an
anterior so-called pseudosucker and a posterior sucker, but lack ciliary
tufts. They have nine receptor types, but no eyes or sensory complex.
Eggs are eaten by snails, and larvae hatch in their stomach. Three snail
species, Cerithium (Clypeomorus) moniliferum, Planaxis sulcatus,andPeristernia
australiensis, all of which live on the beachrock of coral cays, were
found to be naturally infected at Heron Island, Great Barrier Reef.
The first two species were also used in infection experiments, with
positive results. Larvae migrate immediately after hatching along the
ducts of the digestive gland into its follicles. Larvae feed on the secretion
and probably epithelial cells of the digestive gland. The posterior sucker is
used for adhesion to the epithelium and contributes to its erosion. Some
young worms were also found in the stomach of Planaxis, and up to six
worms in the stomach and large digestive ducts of Peristernia. These two
species are larger than Cerithium. Infective juveniles in snails are almost as
large as adults in fish and even contain well developed genitalia and young
sperm and egg cells, which - however - do not mature. Fish become
infected by eating snails, as also demonstrated by infection experiments.
Snails are very thick-shelled and must be crushed between the pharyngeal
plates of the snub-nosed dart. Fish of similar size lacking such strongly
developed pharyngeal plates cannot become infected.
