270
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Description of stage in mollusc. Cobb (1930) has stated that his
description " is probably inadequate for recognizing the nema. . .
This is especially true of the measurements since it is not known at
what stage the larva is in (M. Chitwood, personal communication);
however, as Cobb has pointed out, the description may be of value to
call attention to the fact that such a nematode has been found parasitic
in Aequipecten.
Body (Fig. 175) 16.3 mm long, 0.11 mm wide a t level of mouth,
0.20 mm wide a t level of nerve ring, and 0.13 mm wide a t level of anus ;
nearly colorless ; cuticle with regular transverse striations, with striae
0.008 mm apart a t base of " neck " ; nerve ring 0.36 mm from anterior
end; distance from anterior end to base of esophagus 1.61 mm; esophagus delimited from ventriculus by collum ; with short anteriorly
projecting caecum connected to posterior terminal of ventriculus ; with
three lips (Fig. 175); distinct wings (alae?) beginning on head, near
base of lips, and extending along length of body; excretory pore at
base of lips ; anus 16-02 mm from anterior end.
Other information. No other information is available on P. pectinis.
,,
4. Angiostrongylus cantonensis Chen, 1935. (Figs. 177 and 178)
(Subclass Phasmidia; superfamily Strongyloidea; family Metastrongylidae)
Angiostrongylus cantonensis is a metastrongylid lungworm of rats.
Mackerras and Sandars (1955) have shown that this nematode utilizes
slugs as the intermediate host. Since then, a number of molluscs,
primarily gastropods, have been shown to be suitable intermediate
hosts (see Cheng and Alicata, 1965 ; Alicata, 1965). Normally marine
pelecypods are not infected by this parasite, a t least surveys of clams
and oysters from endemic areas have not revealed natural infections.
However, under certain ambient conditions, Cheng and Burton (1 965a)
have shown that both the young quahaug, Mercenaria mercenaria, and
the American oyster, Crassostrea virginica, can be infected experimentally although the percentage of recovery of third-stage larvae is very
low (Cheng, 1966b). Again, this is not a natural parasite of salt-water
clams and oysters, but it is briefly mentioned here since these pelecypods are known to be suitable experimental intermediate hosts. A
review of the literature pertaining to the role of A . cantonensis as a
causative agent for one type of meningoencephalitis in man in the
Pacific and Southeast Asia has been given by Alicata (1965).
It has been noted (p. 12) that recently Kiiapp and Alicata (1967)
have reported that they were unable to infect Crassostrea virginica
and Venerupis philippinarum (= Tapes semidecussuta) from Hawaii
1
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Description of stage in mollusc. Cobb (1930) has stated that his
description " is probably inadequate for recognizing the nema. . .
This is especially true of the measurements since it is not known at
what stage the larva is in (M. Chitwood, personal communication);
however, as Cobb has pointed out, the description may be of value to
call attention to the fact that such a nematode has been found parasitic
in Aequipecten.
Body (Fig. 175) 16.3 mm long, 0.11 mm wide a t level of mouth,
0.20 mm wide a t level of nerve ring, and 0.13 mm wide a t level of anus ;
nearly colorless ; cuticle with regular transverse striations, with striae
0.008 mm apart a t base of " neck " ; nerve ring 0.36 mm from anterior
end; distance from anterior end to base of esophagus 1.61 mm; esophagus delimited from ventriculus by collum ; with short anteriorly
projecting caecum connected to posterior terminal of ventriculus ; with
three lips (Fig. 175); distinct wings (alae?) beginning on head, near
base of lips, and extending along length of body; excretory pore at
base of lips ; anus 16-02 mm from anterior end.
Other information. No other information is available on P. pectinis.
,,
4. Angiostrongylus cantonensis Chen, 1935. (Figs. 177 and 178)
(Subclass Phasmidia; superfamily Strongyloidea; family Metastrongylidae)
Angiostrongylus cantonensis is a metastrongylid lungworm of rats.
Mackerras and Sandars (1955) have shown that this nematode utilizes
slugs as the intermediate host. Since then, a number of molluscs,
primarily gastropods, have been shown to be suitable intermediate
hosts (see Cheng and Alicata, 1965 ; Alicata, 1965). Normally marine
pelecypods are not infected by this parasite, a t least surveys of clams
and oysters from endemic areas have not revealed natural infections.
However, under certain ambient conditions, Cheng and Burton (1 965a)
have shown that both the young quahaug, Mercenaria mercenaria, and
the American oyster, Crassostrea virginica, can be infected experimentally although the percentage of recovery of third-stage larvae is very
low (Cheng, 1966b). Again, this is not a natural parasite of salt-water
clams and oysters, but it is briefly mentioned here since these pelecypods are known to be suitable experimental intermediate hosts. A
review of the literature pertaining to the role of A . cantonensis as a
causative agent for one type of meningoencephalitis in man in the
Pacific and Southeast Asia has been given by Alicata (1965).
It has been noted (p. 12) that recently Kiiapp and Alicata (1967)
have reported that they were unable to infect Crassostrea virginica
and Venerupis philippinarum (= Tapes semidecussuta) from Hawaii
1