266
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Adults of the four currently recognized species, E. uncinatus, E.
multidentatus, E . southwelli and E. pseudouncinatus, have all been
reported from elasmobranchs (see Millemann, 1963).
Body
10-0-14.5 mm long, coiled, approximately 0.4-0-45 mm in diameter in
anterior portion, 0.7 mm in diameter in posterior portion; lips not
developed in Baylis and Lane’s specimens from Pinna sp. but with
six lips a t anterior terminal (trilobed in adults) in von Linstow’s
specimens from Margaritifera vulgaris; with six (eight 2 ) rows of forty
to fifty hooks per row on slightly bulbous head region with each row
forming a complete circle ; hooks of each row of approximately same
size, measuring 0.047-0.057 mm long ; distances between hooks range
from 0.058 to 0.068 mm ; cuticular striation fine ; esophagus, approximately one-sixth of body length, and long well-developed intestine,
occupying almost all of pseudocoelom ; anus ventral and subterminal.
(For descriptions of adults, see Millemann (1963).)
The life cycle of E. uncinatus remains undetermined
experimentally. Von Linstow (1904) and Baylis and Lane (1920)
have expressed the opinion that the larvae which they found in pelecypods would develop to maturity when parasitized molluscs are ingested
by some elasmobranch definitive host. Since the life cycle of the related
species, E . pseudouncinatus, is known, a t least as determined from
collections of developmental stages from naturally infected hostjs
(Millemann, 1963), and the pattern is essentially that postulated by
von Linstow and Baylis and Lane, it appears that only one intermediate
host, a mollusc, is involved. Earlier reports by von Linstow (1904) and
Johnston and Mawson (1945b) of larvae in teleost fishes suggest that
these fishes may serve as transport (paratenic) hosts. The occurrence
of larvae in sea urchins most probably represents an unnatural condition.
Furthermore, since what appears to be second-stage larvae have been
reported from elasmobranchs (Molin, 1958 ; von Linstow, 1904 ;
Baylis and Lane, 1920; MacCallum, 1921), this may be indicative that
infection of the definitive host can be acquired from the ingestion of
second-stage larvae.
Description of larva in mollusc (of Echinocephalus spp.).
Life cycle.
2. Echinocephalus pseudouncinutusMillemann, 1951. (Figs. 173 and 174)
(Subclass Phasmidia; superfamily Spiruroidea; family Gnathostomat)idae)
As the result of examining pink abalones, Haliotis corrugata, from
Pyramid Cove, San Clemente Island, in southern California, Millemann
(1951) described the larva of another species of Echinocephalus, E.
pseudouncinatus, encysted in the foot of this gastropod. Later (1963),
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Adults of the four currently recognized species, E. uncinatus, E.
multidentatus, E . southwelli and E. pseudouncinatus, have all been
reported from elasmobranchs (see Millemann, 1963).
Body
10-0-14.5 mm long, coiled, approximately 0.4-0-45 mm in diameter in
anterior portion, 0.7 mm in diameter in posterior portion; lips not
developed in Baylis and Lane’s specimens from Pinna sp. but with
six lips a t anterior terminal (trilobed in adults) in von Linstow’s
specimens from Margaritifera vulgaris; with six (eight 2 ) rows of forty
to fifty hooks per row on slightly bulbous head region with each row
forming a complete circle ; hooks of each row of approximately same
size, measuring 0.047-0.057 mm long ; distances between hooks range
from 0.058 to 0.068 mm ; cuticular striation fine ; esophagus, approximately one-sixth of body length, and long well-developed intestine,
occupying almost all of pseudocoelom ; anus ventral and subterminal.
(For descriptions of adults, see Millemann (1963).)
The life cycle of E. uncinatus remains undetermined
experimentally. Von Linstow (1904) and Baylis and Lane (1920)
have expressed the opinion that the larvae which they found in pelecypods would develop to maturity when parasitized molluscs are ingested
by some elasmobranch definitive host. Since the life cycle of the related
species, E . pseudouncinatus, is known, a t least as determined from
collections of developmental stages from naturally infected hostjs
(Millemann, 1963), and the pattern is essentially that postulated by
von Linstow and Baylis and Lane, it appears that only one intermediate
host, a mollusc, is involved. Earlier reports by von Linstow (1904) and
Johnston and Mawson (1945b) of larvae in teleost fishes suggest that
these fishes may serve as transport (paratenic) hosts. The occurrence
of larvae in sea urchins most probably represents an unnatural condition.
Furthermore, since what appears to be second-stage larvae have been
reported from elasmobranchs (Molin, 1958 ; von Linstow, 1904 ;
Baylis and Lane, 1920; MacCallum, 1921), this may be indicative that
infection of the definitive host can be acquired from the ingestion of
second-stage larvae.
Description of larva in mollusc (of Echinocephalus spp.).
Life cycle.
2. Echinocephalus pseudouncinutusMillemann, 1951. (Figs. 173 and 174)
(Subclass Phasmidia; superfamily Spiruroidea; family Gnathostomat)idae)
As the result of examining pink abalones, Haliotis corrugata, from
Pyramid Cove, San Clemente Island, in southern California, Millemann
(1951) described the larva of another species of Echinocephalus, E.
pseudouncinatus, encysted in the foot of this gastropod. Later (1963),