Acanthocephalans of the nominotypical subgenus of Plagiorhynchus ( Plagiorhynchidae ) from charadriiform birds in the collection of the Natural History Museum , London , with a key to the species of the subgenus

Specimens of three species of the nominotypical subgenus of Plagiorhynchus Lühe, 1911 (Acanthocephala, Plagiorhynchidae) are deposited in the Parasitic Worms Collection of the Natural History Museum, London. Two of these species are from birds collected in the United Kingdom: Plagiorhynchus (Plagiorhynchus) crassicollis (Villot, 1875) from Charadrius hiaticula L. and P. (P.) odhneri Lundström, 1942 from C. hiaticula and Haematopus ostralegus L. Th e third species, P. (P.) charadrii (Yamaguti, 1939), is from Charadrius alexandrinus nihonensis Deignan in the Pescadore Islands (near Taiwan). Since the morphology of the three species is poorly known, these specimens are described and fi gured and any variation is commented upon. A key to the species of the subgenus Plagiorhynchus is presented.


Acanthocephalans of the nominotypical subgenus of Plagiorhynchus (Plagiorhynchidae)
from charadriiform birds in the collection of the Natural History Museum, London, with a key to the species of the subgenus Introduction Currently, 11 species of the nominotypical subgenus of Plagiorhynchus Lühe, 1911 (Acanthocephala, Plagiorhynchidae) are considered valid (Lisitsina 1992;Golvan 1994;Smales 2002).Th ey are mainly parasitic in birds of the order Charadriiformes.Th e majority of the species are known on the basis of a few records only.Th erefore, data on their variability are scarce.Th e aim of the present paper is to describe Plagiorhynchus (Plagiorhynchus) spp.from charadriiform birds deposited in the Parasitic Worms Collection of the Natural History Museum, London, in order to provide new data on their morphology, geographical distribution and host-range.In addition, an amended identifi cation key to the species of the subgenus is presented.

Materials and methods
Th is study is based on acanthocephalans from the Parasitic Worms Collection of the Department of Zoology, Natural History Museum, London.In most cases, information on the fi xation methods used is not available.Th e majority of the specimens have been stored in 80% ethanol.For the purposes of the present study, they were cleared in glycerine and water (25-100%) or dimethylphthalate and studied as temporary mounts.Other specimens have been preserved as whole-mounts in Canada balsam.Th e descriptions are based on specimens from a single host specimen and thus one locality.Measurements are given in millimetres, unless otherwise indicated, as a range, with any individual measurements outside the normal range in parentheses.
Th e general distribution of host-species is given in accordance with Encyclopaedia Britannica Online (2009).
Remarks.Th ere are only a few descriptions of this species (Lühe 1911;Petrochenko 1958;Belopol'skaya 1983;del Valle and Coy Otero 1990).Only female specimens were described by Petrochenko (1958) from Phalaropus lobatus (L.) [= P. hyperboreus (L.)] in Kazakhstan.Compared to previous descriptions of the same species (Lühe 1911;Belopol'skaya 1983), the specimens from Kazakhstan diff er in the shape and the length of the trunk (elongate-cylindrical and 17 mm long versus oval and c.7 mm long), the shape of the proboscis (oval versus cylindrical) and the number of longitudinal rows of hooks (16 longitudinal rows of hooks versus 18-20).In addition, there are diff erences in the dimensions of the eggs: 84 × 16 μm (Petrochenko 1958) versus 110 × 49 μm (Lühe 1911).Consequently, it seems likely that the specimens from Kazakhstan described by Petrochenko (1958) belong to another species.
Del Valle and Coy Otero (1990) reported P. crassicollis from Charadrius wilsonia wilsonia Ord in Cuba.According to their description, the armature of the proboscis consists of 18 longitudinal rows of 10-11 hooks per row.However, judging by the drawing of the proboscis (fi gure 1c in del Valle and Coy Otero 1990), the number of hooks per row is at least 18.
One immature female from the same host specimen (Dorset material) possesses a longer proboscis (0.76 mm) and a greater number of hooks per row (15-16).According to these characters, we consider it as belonging to Plagiorhynchus odhneri Lundström, 1942 (see 'Additional data' for P. odhneri).
Remarks.Lundström (1942) described this species from Haematopus ostralegus in Sweden.Golvan (1956) considered it to be a variety of P. crassicollis and later (Golvan 1960) as a subspecies.In the taxonomic arrangement of the nominotypical subgenus of Plagiorhynchus proposed by Schmidt and Kuntz (1966) and Amin (1985), this species is missing.According to other authors (Petrochenko 1958;Yamaguti 1963;Khokhlova 1986;Golvan 1994) , P. odhneri is a valid species.Lisitsina (1992) redescribed it on the basis of specimens from Charadrius dubius Scopoli and C. alexandrinus L. in the Ukraine.
Unfortunately, the type material of this species was not available for re-examination during the course of the present study.Th e studied specimens were identifi ed as P. odhneri mainly on the basis of the proboscis armature (especially with regard to the number of hooks in each longitudinal row).Th e armature (17-20 longitudinal rows of 15-17 hooks) recorded in the present study is within the limits of variation reported by Lundström (1942) in the original description (18-19 longitudinal rows of 14-18 hooks) and by Lisitsina (1992) (18-22 longitudinal rows of 15-19 hooks).
In addition, the proboscis of our worms is shorter, i.e. 0.68 (male) and 0.76-0.8mm (female) compared with 0.8 (male) and 0.9-1.1 mm (female) as recorded by Lundström (1942).However, it is longer than the proboscis of P. crassicollis (0.6 mm) (Lühe 1911).Lisitsina (1992) reported wider limits of variation for this character (0.68-1.23 mm in both sexes), and our specimens fi t within this morphometric range.More abundant material is needed to assess the variation within P. odhneri and to confi rm its validity.
Remarks.Despite the partial invagination of the proboscis, we identifi ed these specimens as Plagiorhychus charadrii based on the number of the longitudinal rows and morphometric data from both the hooks (especially the posterior three or four hooks) and of some internal organs (testes and cement glands).When comparing the present morphometric data with those from published descriptions (Yamaguti 1939;Johnston and Edmonds 1947;Schmidt and Kuntz 1966;Belopol'skaya 1983;Amin et al. 1999;Dimitrova et al. 1999), we did not fi nd signifi cant diff erences, although diff erences in the maximum length of the hook blade are apparent.Regarding the latter feature, the studied specimens are most similar to the descriptions given by Yamaguti (1939), Schmidt and Kuntz (1966) and Dimitrova et al. (1999), i.e. 60-63 versus 59 μm in present specimens.However, Johnston and Edmonds (1947) and Belopol'skaya (1983) reported smaller lengths for the hooks, i.e. 29 and 54 μm, respectively.

Discussion
Th e most recent checklist of the species of the subgenus Plagiorhynchus is that given by Golvan (1994).He considered Plagiorhynchus and Prosthorhynchus as distinct genera (recognised here as subgenera within Plagiorhynchus) and placed 19 species in the former.In my opinion, nine of them do not belong to the subgenus Plagiorhynchus.Th ese are: P. kuntzi Gupta &Fatma, 1987. Gupta andFatma (1987) described this species as a member of Plagiorhynchus on the basis of specimens collected from Buceros bicornis L. [= Dichoceros bicornis (L.)] in India.Th e authors presented ambiguous information relative to the two main features distinguishing the subgenera Plagiorhynchus and Prosthorhynchus, i.e. "eggs with and without polar prolongations" and "female gonopore terminal or subterminal".Furthermore, the host is a forest bird, eating mainly fruit.Th erefore, the position of this species remains uncertain and it cannot be allocated to the subgenus Plagiorhynchus.
P. limnobaeni (Tubangui 1933) Van Cleave & Williams, 1951. Tubangui (1933) described this species on the basis of two male specimens and placed it in Prosthorhynchus.Van Cleave and Williams (1951) transferred it to Plagiorhynchus.Golvan (1956) considered it also in Plagiorhynchus.However, Petrochenko (1958), Yamaguti (1963), Schmidt and Kuntz (1966) and Amin (1985) considered it to belong to Prosthorhynchus, and Amin et al. (1999) included it in their key to the species of the subgenus Prosthorhynchus on the basis of the proboscis armature.Unfortunately, the known features of the male specimens only are not adequate to confi rm the validity of this species or its position within the subgenus Plagiorhynchus.
P. pupa (von Linstow, 1905) Golvan, 1994. Kostylev (1922) redescribed this species on the basis of materials from Somateria molissima L. as Echinorhynchus pupa.Travassos (1926) transferred it to Filicollis Lühe, 1911, but Meyer (1932) proposed it be attributed to Prosthorhynchus.Nevertheless, Petrochenko (1958) listed it among the species of Polymorphus as "Polymorphus pupa (von Linstow, 1905) Kostylew, 1922".Th is generic allocation was followed by Khokhlova (1986) and Amin (1992).According to the ICZN, the valid combination for this species is Polymorphus pupa (von Linstow, 1905) Petrochenko, 1958. P. rectus (Linton, 1892) Van Cleave, 1918.Th e original description was based on one male and one immature female (Van Cleave 1918).Van Cleave (1918) re-examined the female specimen but did not give any details of the female genital system (except mentioning that there were no ripe eggs).Its position in Prosthorhynchus has been accepted by many authors (e.g.Travassos 1926;Meyer 1932;Petrochenko 1958;Amin 1985), but Schmidt and Kuntz (1966) considered it as a species incertae sedis.Th is species was recorded from an aquatic host (Larus sp.).Th e inadequate description of females does not permit its consideration as a species of the subgenus Plagiorhynchus.
Both Johnston and Best (1943) and Smales (2002) redescribed Plagiorhynchus menurae Johnston, 1912 and reported the nerve ganglion as positioned at the posterior end of the proboscis receptacle.However, according to Lühe (1911) and Schmidt and Kuntz (1966), the position of this ganglion is about the middle of the proboscis receptacle for species of the genus Plagiorhynchus.