268
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
As to why the second-stage larva should be larger and its hooks longer
than the older third-stage larva is puzzling.
Life cycire. Millemann (1951, 1963) has described the second stage
larva of E. pseudouncinatus from Haliotis corrugata, and (1963) the
third- and fourth-stage larvae plus the adult from the horned shark,
Heterodontus francisci and the bat sting-ray, Holorhinus ( = Myliobatis)
californicus. Thus, although morphological and survey data strongly
suggest that the larva in the abalone is the second-stage larva of the
stages found in the elasmobranchs, the life cycle pattern reported by
him is not based on experimental feeding experiments but from piecing
together stages collected from naturally infected hosts. The elasmobranch hosts from which Millemann’s specimens were collected were
caught a t San Francisco Bay and Puerto Refugio, Angel de la Guarda
Island, Gulf of California, Mexico.
It is not known whether E. pseudouncinatus is an ovoviviparous or
an oviparous nematode, although the pattern in the family Gnathostomatidae, as exemplified by Gnathostoma spp., includes oviposition
and a free-swimming first-stage larva that hatches after the eggs
remain in water for a period of time (Miyazaki, 1960). It is known,
however, that abalones become infected, not through the ingestion of
eggs or first-stage larvae, but when what is assumed to be first-stage
larvae burrow into the foot.
Ecology. Millemann (1951) has reported that only old abalones are
parasitized. It is not known if this indicates that younger ones are
refractile or if the parasite for some unknown reason prefers older
abalones.
Millemann (1951) has demonstrated that the larvae
burrow into the foot of Haliotis corrugata where they encyst in the
ventral portion, producing a blister-like effect on the exterior of the foot.
Furthermore, he has noted that the vesicatory effect of encysted
larvae in the host’s foot, coupled with the burrowing of the larvae prior
to encystment, apparently weakens the foot musculature and decreases
its efficacy as a hold-fast structure. As the result, parasitized abalones
can be removed from rocks with ease while non-parasitized ones hold
on more rigidly.
Other information. Although Millemann (1951) did not find encysted
larvae in the few specimens of the southern green abalone, Haliotis
fulgens, which he examined, he did report that : (I However, reliable
reports from the divers and the processing plants indicate that the
green abalone is as susceptible to this parasite as the pink abalone, an
indication that the parasite is not host specific.”
Pathology.
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
As to why the second-stage larva should be larger and its hooks longer
than the older third-stage larva is puzzling.
Life cycire. Millemann (1951, 1963) has described the second stage
larva of E. pseudouncinatus from Haliotis corrugata, and (1963) the
third- and fourth-stage larvae plus the adult from the horned shark,
Heterodontus francisci and the bat sting-ray, Holorhinus ( = Myliobatis)
californicus. Thus, although morphological and survey data strongly
suggest that the larva in the abalone is the second-stage larva of the
stages found in the elasmobranchs, the life cycle pattern reported by
him is not based on experimental feeding experiments but from piecing
together stages collected from naturally infected hosts. The elasmobranch hosts from which Millemann’s specimens were collected were
caught a t San Francisco Bay and Puerto Refugio, Angel de la Guarda
Island, Gulf of California, Mexico.
It is not known whether E. pseudouncinatus is an ovoviviparous or
an oviparous nematode, although the pattern in the family Gnathostomatidae, as exemplified by Gnathostoma spp., includes oviposition
and a free-swimming first-stage larva that hatches after the eggs
remain in water for a period of time (Miyazaki, 1960). It is known,
however, that abalones become infected, not through the ingestion of
eggs or first-stage larvae, but when what is assumed to be first-stage
larvae burrow into the foot.
Ecology. Millemann (1951) has reported that only old abalones are
parasitized. It is not known if this indicates that younger ones are
refractile or if the parasite for some unknown reason prefers older
abalones.
Millemann (1951) has demonstrated that the larvae
burrow into the foot of Haliotis corrugata where they encyst in the
ventral portion, producing a blister-like effect on the exterior of the foot.
Furthermore, he has noted that the vesicatory effect of encysted
larvae in the host’s foot, coupled with the burrowing of the larvae prior
to encystment, apparently weakens the foot musculature and decreases
its efficacy as a hold-fast structure. As the result, parasitized abalones
can be removed from rocks with ease while non-parasitized ones hold
on more rigidly.
Other information. Although Millemann (1951) did not find encysted
larvae in the few specimens of the southern green abalone, Haliotis
fulgens, which he examined, he did report that : (I However, reliable
reports from the divers and the processing plants indicate that the
green abalone is as susceptible to this parasite as the pink abalone, an
indication that the parasite is not host specific.”
Pathology.