Hystrignathus rigidus Leidy, 1850

Morffe, Jans, García, Nayla & Davis, Andrew K., 2015, Redescription of the females of Hystrignathus rigidus Leidy, 1850 (Nematoda: Hystrignathidae), parasites of Odontotaenius disjunctus (Coleoptera: Passalidae) from eastern USA, Zootaxa 3941 (1), pp. 131-136 : 132-133

Hystrignathus rigidus Leidy, 1850

Material studied. Vouchers. 10♀♀, USA, Georgia, Athens; in Odontotaenius disjunctus ; 26/IX/2013; A. Davis coll.; CZACC 11.4881-11.4890; 9♀♀, same data as the latter, USNPC; 2♀♀, same data as the latter, CHIOC; 2♀♀, same data as the latter, RIT 833-834.

Measurements. Females (n = 23) a = 11.41–15.15 (13.01 ± 1.05 n = 22), b = 5.79–7.02 (6.44 ± 0.42 n = 12), c = 4.40–6.40 (5.23 ± 0.53 n = 18), V% = 41.96–48.24 (45.88 ± 1.71 n = 15), total length = 2.125–2.950 (2.521 ± 0.221 n = 22), maximum body width = 0.150–0.230 (0.195 ± 0.018 n = 23), first cephalic annule (length×width) = 0.003–0.005×0.033–0.043 (0.004 ± 0.001×0.038 ± 0.003 n = 11) stoma length = 0.043–0.063 (0.057 ± 0.005 n = 22), procorpus length = 0.230–0.330 (0.291 ± 0.023 n = 22), isthmus length = 0.020–0.053 (0.037 ± 0.007 n = 13), diameter of basal bulb = 0.073–0.093 (0.084 ± 0.005 n = 23), total length of oesophagus = 0.350–0.430 (0.399 ± 0.023 n = 13), nerve ring to anterior end = 0.170–0.290 (0.201 ± 0.027 n = 21), excretory pore to anterior end = 0.470–0.750 (0.606 ± 0.055 n = 16), vulva to posterior end = 1.100–1.625 (1.366 ± 0.148 n = 15), tail length = 0.430–0.530 (0.479 ± 0.023 n = 18), eggs = 0.095–0.108×0.038–0.048 (0.102 ± 0.004×0.044 ± 0.003 n = 17).

Redescription. Female body robust, widening from the base of the first cephalic annule, maximum body diameter at level between the base of the oesophagus and the excretory pore, then tapering towards anus. Cuticle markedly annulated in the spiny region, annuli less marked in the rest of the body. Cervical cuticle armed by ca 92 opposite rows of spines, from the end of the first cephalic annule to ca a body width posterior the basal bulb. First row with 16 short spines, ca 4 µm in length, their tips rounded. Next to that row spines become sharp-pointed and increase their length to a maximum of ca 10 µm at rows from 4th to 26th. Spines of the posterior rows diminishing their length to ca 5 µm at level of the final rows. At level of the first third of the spiny region arise additional lines of spines, intercalated between the initial 16, increasing the number of elements of the rows to ca 18. Sub-cuticular longitudinal striae present. Lateral alae absent, but instead a very low ridge is visible extending laterally from the end of the spiny region and surpassing the level of the vulva, then becoming less conspicuous until disappear at the last third of the body. Head cone-like, truncated, set-off from the rest of body by a wide, deep groove. Eight paired, barely prominent papillae around the oral aperture, their shape rounded, with the center depressed, giving a ringlike appearance to the margins. Amphids lateral, pore-like. First cephalic annule very short, ca the half of the head length, its diameter similar to head. Stoma about four head-lengths long, surrounded by an oesophageal collar. Oesophagus consisting of a muscular procorpus, its base slightly inflated, well set-off from the isthmus. Basal bulb rounded, valve plate well developed. Intestine simple, sub-rectilinear. Rectum short, anus not prominent. Nerve ring encircling procorpus at about 40% of its length. Excretory pore situated at about a body width posterior to basal bulb. Vulva a median transverse slit near midbody, lips slightly prominent. Vagina muscular, forwardly directed. Genital tract didelphic-amphidelphic. Oocytes in single rows. Both ovaries reflexed. Anterior ovary reflexed at the level of the excretory pore, distal flexure ca 2.3 body-widths length. Posterior ovary reflexed at ca 2.5 body-widths anterior to the level of the anus, distal flexure ca 2.2 body-widths long. Eggs ovoid, shell with eight rough, longitudinal, hardly prominent ridges. A number of 6 to 19 eggs at a time in the uteri. Tail conical, attenuate, ending in a fine tip.

Host. Odontotaenius disjunctus ( Coleoptera : Passalidae ).

Site of infestation. Hind gut.

Locality. Athens, Georgia, USA.

Differential diagnosis. H. rigidus can be differentiated from H. coyi García, Ventosa & Morffe, 2009 ; H. inflatus Travassos & Kloss, 1957 ; H. splendidus Morffe & García, 2010 and H. tarda (Artigas, 1928) Travassos & Kloss, 1958 by having a short and not inflated first cephalic annule vs. the longer and notably inflated one of the latter species ( García et al. 2009; Morffe & García 2010b; Travassos & Kloss 1957a; 1958). H. rigidus can also be readily segregated from several species of the genus by the extension of its spines, which surpasses the level of the oesophagus. Most of the Hystrignathus present spines that do not extend further down the oesophagus level: H. cobbi Travassos & Kloss, 1957 ; H. dearmasi Morffe & García, 2010 ; H. egalis van Waerebeke & Remillet, 1982; H. heliae Travassos & Kloss, 1957 ; H. inegalis van Waerebeke & Remillet, 1982; H. insularis van Waerebeke, 1973; H. meridensis Guerrero, 1980 ; H. metropolitanus Cordeiro, 1981 ; H. papillophorus Cordeiro, 1981 and H. popiliophagus Guerrero, 1980 ( Cordeiro 1981; Guerrero 1980; Morffe & García 2010a; Travassos & Kloss 1957b; van Waerebeke 1973; van Waerebeke & Remillet 1982).

The species with spines surpassing the level of the oesophagus are H. ferox Hunt, 1982 ; H. paulistanus Cordeiro, 1981 ; H. pearsoni Travassos & Kloss, 1958 ; H. rosario García, Ventosa & Morffe, 2009 ; H. rugosus Travassos & Kloss, 1958 and H. spinosus Travassos & Kloss, 1957 ( Cordeiro 1981; García et al. 2009; Hunt 1982; Travassos & Kloss 1957a; 1958). From the latter taxa (excluding H. paulistanus ) that present lateral alae well developed, H. rigidus differs by lacking of such structures, which are substituted by low cuticular ridges. Besides, H. paulistanus , H. pearsoni and H. spinosus present smooth-shelled eggs in opposition to the ridged-shelled eggs of H. rigidus .

H. rigidus can be differentiated from H. ferox by having a shorter body (present material 2.125–2.950, Christie`s material 2.130–4.200 vs. 4.500–5.070) ( Christie 1934; Hunt 1982). H. rosario present the tail comparatively longer than H. rigidus (c = 3.38–3.98 vs. present material 4.40–6.40, Christie´s material 4.43–7.69) ( Christie 1934; García et al. 2009).

In the original description of H. paulistanus Cordeiro did not mention the existence or absence of lateral alae. However, H. paulistanus differs (in addition to the smooth eggs) by having a longer first cephalic annule, not surpassed by the stoma ( Cordeiro 1981).

Comments. The specimens from the present study mostly agree with the morphology and morphometrics given in the redescription by Christie (1934). The more evident differences are the longer body (2.130–4.200 vs. 2.125–2.950) and the oesophagus (0.650–0.670 vs. 0.350–0.430) in Christie´s specimens. Moreover, the first cephalic annule is shorter in our material (0.003–0.005 vs. 0.012). Also of note is that both Leidy (1850) and Christie (1934) did not mention the presence of ornamentations on the egg surfaces. In our material the eggs present eight evident ridges in the shell, as occurs in several species of the genus and hystrignathids as well.

H. rigidus has been recorded for multiple states in the eastern USA, including Illinois, Louisiana, Maryland, Pennsylvania and Virginia ( Christie 1934), as well as North Carolina ( Pearse et al. 1936) and South Carolina ( Reinert 1973), consistent with the distribution of its host O. disjunctus ( Schuster 1983) . The current study constitutes a new locality record for the species.

Christie (1934) stated that in all the examined hosts, H. rigidus was associated to Xyo pseudohystrix Travassos & Kloss, 1958 . Frequently, the author also found male specimens belonging to a single morphotype. Being unable to assign such males to one of the two species, the author assigned them, arbitrarily and provisionally, to H. rigidus . Before such problems, further studies on new material are needed in order to describe and assign properly the males of the both, H. rigidus and X. pseudohystrix . In that sense, molecular markers such as the 28S rDNA have proven to be useful for confirming conespecificity of males and females among Thelastomatoidea ( Guzeeva et al. 2010; Spiridonov & Cribb 2012).