igO FLEAS, FLUKES AND CUCKOOS 



of waders, such as the ringed plover, Kentish plover, sanderling, 

 dunlin and oystercatchcr. It has also been recorded from the cuckoo. 

 At first sight it appears curious that the cuckoo should share a parasite 

 with this group of birds. On the other hand wagtails, which often act as 

 their foster parents, are infected with certain trematodes which other- 

 wise are chiefly found in waders. One can surmise that Crustacea form 

 a certain proportion of the wagtail's diet and the cuckoo may have 

 been fed the larvae as a nestling by its foster parents. Another species 

 found in waders in Britain is Arhythmorhynchus longicollis from the purple 

 sandpiper. It is also fairly common in gulls. Finally there is the 

 characteristic duck parasite Filicollis anatis recorded from the mallard 

 and scaup in Britain. It has a similar life history to P. boschadis^ using 

 hog slaters [Asellus aquaticus) as intermediate host. There are only two 

 species in this genus, one from Europe where it is also occasionally 

 found in moorhens and coots, and another from South America where 

 it parasitises gulls. In this genus the proboscis is bulbous and when 

 implanted in the intestinal wall of the host forms a powerful ball anchor 

 as the tissue of the host contracts round the narrow "neck" portion 

 below the bulb. 



For such a small group acanthocephalids infect a really large variety 

 of birds. In 1933, Meyer listed over 300 host species, ranging from 

 penguins to eagles, and kingfishers to wood-warblers. The most heavily 

 afflicted family is the ducks (Anatidae), but waders, birds of prey and 

 thrushes are among the groups which are heavily attacked. The rock- 

 thrush which has a wide distribution in Asia, India, North Africa and 

 the Falaearctic region and has been recorded about eight times in 

 Britain, acts as an intermediate host for Echinorhynchus pachy acanthus, 

 which reaches maturity in predatory mammals such as the lynx {Felis 

 lynx) and jackal {Canis aureus). 



The most impressive feature of an acanthocephalid is undoubtedly 

 the retractile proboscis (see Fig. 4 (3)) with which it anchors 

 itself to the host — for " it was all grown over with thorns." 

 These proboscis hooks are valuable characters for use in classifying the 

 whole group. In three of the four main orders, the spines are arranged 

 radially in long rows on the proboscis, but in the fourth order the 

 arrangement is in the form of a spiral. In two of these orders the trunk 

 spines are absent, but they are present in the others. They are also used 

 as aids for the diagnosis of lower categories such as the families, genera 

 and species. There are thin spines and stout spines, broad, long, stumpy. 



