7. THE PHYLA NEMERTINEA, ASCHELMINTHES AND ANNELIDA
265
The few definitely identified species of nematodes from commercially
important marine molluscs have all been juveniles or larvae. These are
reviewed below.
1. Echinocephalus uncinatus Molin, 1858( ‘ 1)
(Subclass Phasmidia; superfamily Spiruroidea; family Gnathostomatidae)
Molin (1858) erected the genus Echinocephalus to include E. uncinatus
the larvae of which are found in the spiral valves of the ray Trygon
brucco in the Adriatic Sea. The original description was based on two
distinct types of specimens. Molin (1858, 1861) designated one specimen,
7.0 mm long with six rows of cephalic hooks, as the female, and two
others, 24-35 mm long with thirty rows of hooks, as males. Baylis and
Lane (1920) considered Molin’s males to be identical with another
species, E. spinosissimus, and the female to be distinct and selected it
as the true E. uncinatus. More recently, Millemann (1963), who has
contributed a thorough study of this genus, stated :
It is now clear, as shown in the present study, that the early juvenile stages
of E. pseudouncinatus, and probably of other species as well, have 8 rows of
of hooks (the first 2 rows are easily overlooked unless en face preparations are
studied and this would account for the reports of juveniles with only 6 rows
of hooks). The definitive number of rows is attained at the third-stage molt.
This evidence, and t h e fact that adults of E. uncinatus have never been found,
strongly suggests that Molin’s “ female ” and all other specimens with 6 (8Z)
rows of hooks assigned to the species uncinatus by different authors. . . are
actually early juvenile stages of known or unknown echinocephalids.
Furthermore, Millemann has designated Molin’s male as the true
E. uncinatus and considered E. spinosissimus to be its synonym.
Earlier, von Linstow (1904) had found what he assumed to be the
larva of E . uncinatus encysted in the adductor muscle of the pearl
oyster, Margaritifera vulgaris, in Ceylonese waters, and Baylis and Lane
(1920) had reported this larva in the pelecypod Pinna sp. and immature adults in the sting-ray, Myliobatis nieuhoji, in Ceylon. In
addition, Hopkins (1935) has described what he believed to be the larva
of E. uncinatus collected by Van Cleave in the gonad of the sea urchin,
Arbacia punctulata, a t Woods Hole, Massachusetts, and Johnston
and Mawson (1945a) have reported this larva from Polinices conica
and Katylesia scalarina from Australian waters. As the result of
Millemann’s (1963) studies, it may now be said that the larval echinocephalids found by von Linstow, Baylis and Lane, Hopkins, an
Johnston and Mawson cannot be definitely designated as E. uncinatus
265
The few definitely identified species of nematodes from commercially
important marine molluscs have all been juveniles or larvae. These are
reviewed below.
1. Echinocephalus uncinatus Molin, 1858( ‘ 1)
(Subclass Phasmidia; superfamily Spiruroidea; family Gnathostomatidae)
Molin (1858) erected the genus Echinocephalus to include E. uncinatus
the larvae of which are found in the spiral valves of the ray Trygon
brucco in the Adriatic Sea. The original description was based on two
distinct types of specimens. Molin (1858, 1861) designated one specimen,
7.0 mm long with six rows of cephalic hooks, as the female, and two
others, 24-35 mm long with thirty rows of hooks, as males. Baylis and
Lane (1920) considered Molin’s males to be identical with another
species, E. spinosissimus, and the female to be distinct and selected it
as the true E. uncinatus. More recently, Millemann (1963), who has
contributed a thorough study of this genus, stated :
It is now clear, as shown in the present study, that the early juvenile stages
of E. pseudouncinatus, and probably of other species as well, have 8 rows of
of hooks (the first 2 rows are easily overlooked unless en face preparations are
studied and this would account for the reports of juveniles with only 6 rows
of hooks). The definitive number of rows is attained at the third-stage molt.
This evidence, and t h e fact that adults of E. uncinatus have never been found,
strongly suggests that Molin’s “ female ” and all other specimens with 6 (8Z)
rows of hooks assigned to the species uncinatus by different authors. . . are
actually early juvenile stages of known or unknown echinocephalids.
Furthermore, Millemann has designated Molin’s male as the true
E. uncinatus and considered E. spinosissimus to be its synonym.
Earlier, von Linstow (1904) had found what he assumed to be the
larva of E . uncinatus encysted in the adductor muscle of the pearl
oyster, Margaritifera vulgaris, in Ceylonese waters, and Baylis and Lane
(1920) had reported this larva in the pelecypod Pinna sp. and immature adults in the sting-ray, Myliobatis nieuhoji, in Ceylon. In
addition, Hopkins (1935) has described what he believed to be the larva
of E. uncinatus collected by Van Cleave in the gonad of the sea urchin,
Arbacia punctulata, a t Woods Hole, Massachusetts, and Johnston
and Mawson (1945a) have reported this larva from Polinices conica
and Katylesia scalarina from Australian waters. As the result of
Millemann’s (1963) studies, it may now be said that the larval echinocephalids found by von Linstow, Baylis and Lane, Hopkins, an
Johnston and Mawson cannot be definitely designated as E. uncinatus