W. H. Leigh-Sharpe 
275 
Platybdella anarrhichae (Diesing 1858) 1 as defined by Malm 1863, and 
not Trachelobdella as would have been expected in view of the above 
statement that Henry had found T. lubrica (?) commonly on the catfish. 
Habitat. Platybdella anarrhichae is parasitic on Anarrhichas lupus, 
the wolf-fish or catfish, on the gills, the walls of the branchial chamber, 
and has been found on the pectoral region in general, both on young 
and adult fish, in enormous numbers. It continues to live for days 
after the fish are dead and gutted and packed in ice. Dr Henry tells 
me he has found a single specimen of the leech (if the same) on an adult 
Coitus bubalis taken at Robin Hood’s Bay. The leech is frequently 
found on the shores of Scotland, but it is much rarer on the eastern 
shores of the North Sea, i.e. in Norway, according to Johansson. 
Body. The body of the leech is cylindrical, only moderately 
depressed, without papillae or respiratory vesicles, divided, though not 
very distinctly, into an anterior “neck,” and a posterior abdomen. 
The animal, when at rest, does not curl itself up. The posterior part of 
the body is but little broader than the anterior. There are no eyes. 
The skin is extraordinarily smooth, but when the leech is alive and on 
the host the skin is more winkled (Hesse). The annuli can only be 
made out with difficulty. The colour of the animal is pale grey, or 
greyish white, bordering on yellow with reddish streaks fore and aft, 
but more noticeable posteriorly. To my mind these red streaks are 
caused solely by the colour of the oxyhaemoglobin of the ingested blood 
of the host in the digestive tract being visible through the skin, which 
is remarkably diaphanous, the internal organs being most easily observed 
through it in a mounted specimen. Greenish spots appear here and 
there. The average length of my spirit preserved specimens, which 
still show plainly the reddish streaks, is 2-5 cm., showing that they 
attain a length of 3 or 4 cm., as stated in various reports, and a width 
of about 2 mm. 
1 This is probably the same leech as that described as Iclithyobdella anarrhichae, 
(Diesing) by van Beneden and Hesse, and most certainly the Platybdella anarrhichae 
described by Malm. The diagnosis given by Diesing is so vague that I should hesitate 
to recognize a specimen from it, whereas the leeches are easily identified from the text 
of Malm, and particularly from the figure. Blanchard does not mention Platybdella 
except as a synonym for Cystibranchus (Cystobranchus ), which it obviously is not in the 
now-accepted definition of the latter genus. Platybdella is not particularly flattened, 
hence the name is a misnomer. The facts of the case are that the animal now known as 
Cystibranchus mammillatus was a Platybdella according to the loose diagnosis of such 
authors as Diesing and Malm; hence Malm’s definitions have had to be in this case con¬ 
siderably amended. 
