6. THE PHYLA PORIFERA, CNIDARIA AND PLATYHELMINTHES
225
16. Cercaria dichotoma La Valette, 1855. (Figs. 135 and 136)
superfamily Fellodistomatoidea ; family Fellodistomatidae)
(Superorder Anepitheliocystidia; order Strigeatoidea; suborder Az ygiata;
Cercaria dichotoma was first found by Muller free in the Mediterranean near Nice, hence the designation C. dichotoma Miiller as used by
Lebour (1908, 1911), Stunkard and Uzmann (1958) and Hutton (1952).
But it was described by La Valette (1855) from the marine pelecypod
Scrobicularia tenuis. Villot (1878) believed that it was identical to La
Valette’s Cercaria Jissicauda but, as Pelseneer (1906) has pointed out,
this could not be since C. Jissicauda was described from a freshwater
gastropod, Lymnaea stagnalis. I n the same paper, Pelseneer reported
C. dichotoma from Tellina solidula (= Macoma balthica) from deep
water near Boulogne-sur-Mer, France, and recognized that C. dichotoma
is extremely similar to an unnamed cercaria described by Huet (1888b)
from Cardium edule collected along the coast of Normandy. But, as
indicated in the following section, Huet’s cercaria cannot be C . dichotoma. Johnstone (1904) has reported C. dichotoma from Cardium edule
from the Lancashire coast and Lebour (1908, 1911) has also reported its
occusreiice in Scrobicularia tenuis collected at Fenham Flats, England.
Thus it would appear from what is known that this cercaria utilizes a
marine pelecypod as the first intermediate host but is not restricted to
a single species. Furthermore, if Johnstone’s identification is correct,
it has been found in a commercially important species, Cardium edule.
Description. Sporocyst (Fig. 135) long and irregular, about 1 mm
long, more pointed at one end than other, very transparent, filled with
cercariae a t all stages of development. Cercaria (Fig. 136) with bifurcated tail, 0.20 mm long with tail; tail slightly shorter than body;
anterior sucker 0.033 mm in transverse diameter ; prepharynx absent ;
pharynx 0.016 mm long ; esophagus long ; intestinal caeca reaching
slightly beyond anterior level of ventral sucker; ventral sucker in
posterior half of body, 0.029 mm in transverse diameter; excretory
vesicle said to be lyre-shaped, actually Y-shaped with arms slightly
convoluted, occupying most of posterior half of body, arms reaching
midlength of body anteriorly, stem extending into tail, bifurcating, and
terminating at tips of furcae.
Other information. No other information is available on C. dichotoma
except for the statement by James et al. (1966) that:
We have made some unpublished histochemical and electron-microscope
observations on the tegument of the daughter sporocyst of Cercaria dichomata
Lebour, 1911 (James et al. have erroneously credited this species to Lebour),
which suggest that the outer region and the middle nucleated and secretory
A.X.B.--6
16
225
16. Cercaria dichotoma La Valette, 1855. (Figs. 135 and 136)
superfamily Fellodistomatoidea ; family Fellodistomatidae)
(Superorder Anepitheliocystidia; order Strigeatoidea; suborder Az ygiata;
Cercaria dichotoma was first found by Muller free in the Mediterranean near Nice, hence the designation C. dichotoma Miiller as used by
Lebour (1908, 1911), Stunkard and Uzmann (1958) and Hutton (1952).
But it was described by La Valette (1855) from the marine pelecypod
Scrobicularia tenuis. Villot (1878) believed that it was identical to La
Valette’s Cercaria Jissicauda but, as Pelseneer (1906) has pointed out,
this could not be since C. Jissicauda was described from a freshwater
gastropod, Lymnaea stagnalis. I n the same paper, Pelseneer reported
C. dichotoma from Tellina solidula (= Macoma balthica) from deep
water near Boulogne-sur-Mer, France, and recognized that C. dichotoma
is extremely similar to an unnamed cercaria described by Huet (1888b)
from Cardium edule collected along the coast of Normandy. But, as
indicated in the following section, Huet’s cercaria cannot be C . dichotoma. Johnstone (1904) has reported C. dichotoma from Cardium edule
from the Lancashire coast and Lebour (1908, 1911) has also reported its
occusreiice in Scrobicularia tenuis collected at Fenham Flats, England.
Thus it would appear from what is known that this cercaria utilizes a
marine pelecypod as the first intermediate host but is not restricted to
a single species. Furthermore, if Johnstone’s identification is correct,
it has been found in a commercially important species, Cardium edule.
Description. Sporocyst (Fig. 135) long and irregular, about 1 mm
long, more pointed at one end than other, very transparent, filled with
cercariae a t all stages of development. Cercaria (Fig. 136) with bifurcated tail, 0.20 mm long with tail; tail slightly shorter than body;
anterior sucker 0.033 mm in transverse diameter ; prepharynx absent ;
pharynx 0.016 mm long ; esophagus long ; intestinal caeca reaching
slightly beyond anterior level of ventral sucker; ventral sucker in
posterior half of body, 0.029 mm in transverse diameter; excretory
vesicle said to be lyre-shaped, actually Y-shaped with arms slightly
convoluted, occupying most of posterior half of body, arms reaching
midlength of body anteriorly, stem extending into tail, bifurcating, and
terminating at tips of furcae.
Other information. No other information is available on C. dichotoma
except for the statement by James et al. (1966) that:
We have made some unpublished histochemical and electron-microscope
observations on the tegument of the daughter sporocyst of Cercaria dichomata
Lebour, 1911 (James et al. have erroneously credited this species to Lebour),
which suggest that the outer region and the middle nucleated and secretory
A.X.B.--6
16