6. THE PHYLA PORIFERA, CNIDARIA AND PLATYHELMINTKES
213
Worm reported the occurrence of pearly formations in the mantle of
Mytilus edzilis collected a t Roeskild, near Copenhagen. The information
available on worm-associated pearl formation has been reviewed in
Chapter 4, Section 11, A, 2. Interest in this phenomenon led Dubois
(1901) to study the parasit&es of M . edulis a t Billiers. He found trematodes (now known to be metacercariae) measuring 0-4-0.6 mm in length
in reddish brown spots which are the loci of pearl formation. He
named the parasite Distomum margaritarum. He also found the same
or a very similar parasite in M ytilus galloprovincialis from the coast of
Provence. Later (Dubois, 1907)) he placed this trematode in the genus
Gymnophallus. Since Dubois' initial study, various individuals have
examined this parasite. Jameson (1902), who has also examined the
parasites of Mytilus edulis at Billiers, described and depicted worms
which he believed to closely resemble Gymnophallus ( = Distomum)
somateriae, the adult of which was described by Levinsen (1881) from
the intestine of the eider duck, Somateria mollissima, captured near
Egedesminde, Greenland. I n following Stossich (1899), Jameson,
however, relegated his specimens to the genus Lecithodendrium as L.
somateriae. I n addition to Mytilus edulis from Billiers, Jameson has
also reported the occurrence of similar larvae (now known t o be cercariae)* in sporocysts in Tapes decussatus from the same location, larvae
(metacercariae) in Mytilus edulis from Piel, Barrow, Lancashire,
England*, sporocysts in Cardium edule from Piel, and adult worms from
the intestine of the scoter, Melanitta ( = Oidemia) nigra, a t Billiers.
Although he described and depicted what he considered the adult of
L. somateriae to be 0.2-0.55 mm long, which is about one-half the size
of the larvae (metacercariae) in Mytilus edulis, he concluded that
morphological similarity between the metacercaria in M . edulis and
adult Lecithodendrium somateriae and the fact that the adults were
found in two species of mussel-eating birds were sufficient proof that the
metacercariae are the larvae of L. somateriae. His conclusion, of course,
is not acceptable.*
Lebour (1911) has designated the cercariae found in Cardium edule
and Tapes decussatus as Cercaria margaritae sp. inq. ( = the Pearl
Trematode of Jameson (1902)).* She also has reported metacercariae
encysted in Mytilus edulis. Lebour (1911) pointed out that she had
earlier found the same sporocyst in Cardium (Lebour, 1907a) as had
Nicoll (1906a), but both of them had found the sporocystst just beneath
the umbo where they were embedded in a jelly-like mass frequently
embedded with " chalky spots ) ) rather than in the muscular or connective tissue of the mantle edge, particularly dorsally, close t o the
* See note to p. 218 on p. 390. t See note on p. 389.
213
Worm reported the occurrence of pearly formations in the mantle of
Mytilus edzilis collected a t Roeskild, near Copenhagen. The information
available on worm-associated pearl formation has been reviewed in
Chapter 4, Section 11, A, 2. Interest in this phenomenon led Dubois
(1901) to study the parasit&es of M . edulis a t Billiers. He found trematodes (now known to be metacercariae) measuring 0-4-0.6 mm in length
in reddish brown spots which are the loci of pearl formation. He
named the parasite Distomum margaritarum. He also found the same
or a very similar parasite in M ytilus galloprovincialis from the coast of
Provence. Later (Dubois, 1907)) he placed this trematode in the genus
Gymnophallus. Since Dubois' initial study, various individuals have
examined this parasite. Jameson (1902), who has also examined the
parasites of Mytilus edulis at Billiers, described and depicted worms
which he believed to closely resemble Gymnophallus ( = Distomum)
somateriae, the adult of which was described by Levinsen (1881) from
the intestine of the eider duck, Somateria mollissima, captured near
Egedesminde, Greenland. I n following Stossich (1899), Jameson,
however, relegated his specimens to the genus Lecithodendrium as L.
somateriae. I n addition to Mytilus edulis from Billiers, Jameson has
also reported the occurrence of similar larvae (now known t o be cercariae)* in sporocysts in Tapes decussatus from the same location, larvae
(metacercariae) in Mytilus edulis from Piel, Barrow, Lancashire,
England*, sporocysts in Cardium edule from Piel, and adult worms from
the intestine of the scoter, Melanitta ( = Oidemia) nigra, a t Billiers.
Although he described and depicted what he considered the adult of
L. somateriae to be 0.2-0.55 mm long, which is about one-half the size
of the larvae (metacercariae) in Mytilus edulis, he concluded that
morphological similarity between the metacercaria in M . edulis and
adult Lecithodendrium somateriae and the fact that the adults were
found in two species of mussel-eating birds were sufficient proof that the
metacercariae are the larvae of L. somateriae. His conclusion, of course,
is not acceptable.*
Lebour (1911) has designated the cercariae found in Cardium edule
and Tapes decussatus as Cercaria margaritae sp. inq. ( = the Pearl
Trematode of Jameson (1902)).* She also has reported metacercariae
encysted in Mytilus edulis. Lebour (1911) pointed out that she had
earlier found the same sporocyst in Cardium (Lebour, 1907a) as had
Nicoll (1906a), but both of them had found the sporocystst just beneath
the umbo where they were embedded in a jelly-like mass frequently
embedded with " chalky spots ) ) rather than in the muscular or connective tissue of the mantle edge, particularly dorsally, close t o the
* See note to p. 218 on p. 390. t See note on p. 389.