Family Rhabdiasidae (Nematoda)
ABOUT SPECIES LIST TAXONOMY BIOLOGY KEYS BIBLIOGRAPHY PROJECT AUTHORS

Taxonomy

The genus Rhabdias Stiles et Hassall, 1905 was erected without any diagnosis, just the type species, R. bufonis (Schrank, 1788), was indicated. The emended diagnoses for the genus were published by Travassos (1930), Yamaguti (1961) and Baker (1978).

Pereira (1927) discovered the new species which he placed into a new genus Acanthorhabdias Pereira, 1927. The differentiation from Rhabdias Stiles et Hassall, 1905 was based on the differences in cephalic end morphology: from 8 to 10 cone-shaped circumoral protuberances found in A. acanthorhabdias Pereira, 1927 which have never been observed in Rhabdias spp.

Travassos (1930) proposed the new genus Entomelas Travassos, 1930 for 3 species previously belonging to Rhabdias Stiles et Hassall, 1905: E. entomelas (Dujardin, 1845), E. dujardini (Maupas, 1916) and E. chameleonis (Skrjabin, 1916). The differentiation of the two genera was based on the differences in buccal capsule size, small in Rhabdias spp. and enlarged in Entomelas spp. Taken into account were absolute dimensions of buccal capsule, without respect to the body size of the worms. E. entomelas (Dujardin, 1845) was indicated as type species for the genus. In the same paper Travassos (1930) also gave brief diagnoses for the genera Rhabdias Stiles et Hassall, 1905, Acanthorhabdias Pereira, 1927 and Entomelas Travassos, 1930.

Yamaguti (1943) described the species Rhabdias horigutii Yamaguti, 1943 and proposed to place it into the subgenus Ophiorhabdias Yamaguti, 1943. Differentiation from the nominative subgenus Rhabdias was based on the absence of buccal capsule in R. (Ophiorhabdias) horigutii Yamaguti, 1943 and its specificity to snakes. However, the differentiation was not absolutely correct since subgenus Rhabdias was regarded as including only amphibian parasites. The species R. fuscovenosa (Railliet, 1899), R. vellardi Pereira, 1928, R. ophidia Goodey, 1924 and R. labiata Pereira, 1928, all possessing the buccal capsules, were not mentioned by Yamaguti (1943). Later Sharpilo (1976) elevated the rank of the subgenus Ophiorhabdias Yamaguti, 1943 to generic level.

Sharpilo (1964) transferred the species Hexadontophorus ophisauri Kreis, 1940 from Strongylidae to Rhabdiasidae. The similarities between H. ophisauri Kreis, 1940 and Entomelas spp. were emphasised, however, the generic position of the species was left unchanged and the differential diagnosis for the genus Hexadonthophorus Kreis, 1940 was not emended.

Ballantyne and Pearson (1963) transferred Pneumonema tiliquae Johnston, 1916 from Rictulariidae to Rhabdiasidae reffering to the close morphological and biological affinities between the species and other rhabdiasids. The genus Pneumonema Johnston, 1916 was differentiated from all genera of Rhabdiasidae on the base of presence of cuticular spines in P. tiliquae Johnston, 1916.

Szczerbak and Sharpilo (1969) proposed the new genus Kurilonema Szczerbak et Sharpilo, 1969 for the species K. markovi Szczerbak et Sharpilo, 1969. The genus was distinguished from Rhabdias Stiles et Hassall, 1905 by notably larger buccal capsule, and from Entomelas Travassos, 1930 by the absence of teeth.

Singh (1975) described a new rhabdiasid species Shortia shortii Singh (1975) which he placed into the new genus Shortia Singh, 1975. The new genus was differentiated from Rhabdias Stiles et Hassall, 1905 based on the presence of hypodermal glands - "areoles" in S. shortii Singh, 1975.

Sharpilo (1976) proposed the new genus Paraentomelas Sharpilo, 1976 for two species P. dujardini (Maupas, 1916) and P. kazachstanica (Sharpilo et Vakker, 1972) previously belonging to the genus Entomelas Travassos, 1930. The author believed that Paraentomelas species differed from Entomelas ones in swollen body cuticle and needle-like tail tip.

The revision of the genus Entomelas Travassos, 1930 and related genera has been performed by Baker (1980). In fact, all genera within the family were involved. The author synonymized the genera Kurilonema Szczerbak et Sharpilo, 1969, Hexadontophorus Kreis, 1940 and Paraentomelas Sharpilo, 1976 with the genus Entomelas Travassos, 1930, and the genera Ophiorhabdias Yamaguti, 1943 and Shortia Singh, 1975 with the genus Rhabdias Stiles et Hassall, 1905. The species Entomelas chameleonis (Skrjabin, 1916) Travassos, 1930 was transferred to the genus Rhabdias Stiles et Hassall, 1905; three species: P. dujardini (Maupas, 1916), P. kazachstanica (Sharpilo et Vakker, 1972) and H. ophisauri Kreis, 1940 were synonymized with E. entomelas (Dujardin, 1845).

The synonymizations were based on the peculiarities of late parasitic development of two Rhabdias species (Baker, 1979) (the data were extrapolated to Entomelas spp. development) and author's attitude towards significance or insignificance of some morphological characters (e. g. presence or absence of teeth or buccal capsule, number of teeth, size of buccal capsule, etc.). As the result, only 4 generic names were left valid within Rhabdiasidae Railliet, 1916:

  1. Acanthorhabdias Pereira, 1927
  2. Entomelas Travassos, 1930
  3. Pneumonema Johnston, 1916 and
  4. Rhabdias Stiles et Hassall, 1905.

This system was accepted in the "CIH Keys to nematode parasites of vertebrates, No. 9" (Anderson, Bain 1982).

Hasegawa (1989) described a new rhabdiasid species with quite an aberrant head end morphology and proposed the new genus Neoentomelas Hasegawa, 1989 for it. The genus was differentiated from Entomelas Travassos, 1930 (sensu Baker 1980) by the presence of dorsal and ventral pseudolabia and markedly enlarged head end bearing posterior lobes.

Recently Lhermitte-Vallarino, Bain, Deharo et al., (2005) erected new genus Chabirenia Lhermitte-Vallarino, Bain, Deharo et al., 2005 for one species of rhabdiasids, Chabirenia cayennensis, found in buccal cavity of lizards. In addition to abnormal localization, the new species possesses longitudinal cuticular ridges similar to synlophe of trichostrongylid nematodes.

The data obtained by the authors of the present issue do not allow to agree completely with the results of Baker's revision. The investigations on the post-embryonic development of 4 Entomelas species from anguid lizards, as well as the molecular studies, have proved the validity of the species E. dujardini (Maupas, 1916), E. kazachstanica Sharpilo et Vakker, 1972 and H. ophisauri Kreis, 1940 (Kuzmin 1996). However, six teeth present in these 3 species, as well as in E. entomelas (Dujardin, 1845) and in E. cruszi Baker, 1980 should be considered, in our opinion, as the diagnostic character for the genus Entomelas Travassos, 1930. From this point of view, the synonymization of Paraentomelas Sharpilo, 1976 and Hexadonthophorus Kreis, 1940 with Entomelas Travassos, 1930 is considered to be justified.

On the other hand, K. markovi Szczerbak et Sharpilo, 1969 should not be placed into Entomelas Travassos, 1930 since teeth are absent in this species. The generic position of Entomelas sylvestris Baker, 1982 is disputable. The species is characterised by three teeth and buccal capsule divided into anterior thick-walled and posterior thin-walled parts (Baker 1982). These characters differ the species from other Entomelas spp. and from all rhabdiasids as well. Moreover, E. sylvestris was described from amphibians (Breviceps sylvestris: Anura, Microhylidae), whereas the other species of the genus are known to parasitize lizards.

The following system of the family is accepted herein.

Family Rhabdiasidae Railliet, 1916

  1. Genus Rhabdias Stiles et Hassall, 1905
  2. Genus Acanthorhabdias Pereira, 1927
  3. Genus Chabirenia Lhermitte-Vallarino, Bain, Deharo et al., 2005
  4. Genus Entomelas Travassos, 1930
  5. Genus Kurilonema Szczerbak et Sharpilo, 1969
  6. Genus Neoentomelas Hasegawa, 1989
  7. Genus Pneumonema Johnston, 1916