Rhigonema nesoboli, García & Morffe, 2014

García, Nayla & Morffe, Jans, 2014, A new species of Rhigonema Cobb, 1898 (Nematoda: Rhigonematidae) from a Cuban spirobolid millipede (Diplopoda: Spirobolida), Papéis Avulsos de Zoologia (São Paulo) 54 (1), pp. 1-8 : 2-7

Rhigonema Cobb, 1898 Rhigonema nesoboli sp. nov.

( Fig. 1 A-E, Fig. 2 A-D, Fig. 3 A-D)

Type material: ♀ holotype, Cuba, Santiago de Cuba province, La Gran Piedra, La Isabelica, 75°37’18.80”N, 20°00’32.68”W ; in Nesobolus piedra ; IV/2009; J. Morffe coll.; CZACC 11.4580 . Paratypes 7 ♀♀, same data as holotype, CZACC 11.4581 -11.4587 ; 6 ♂♂, same data as holotype, CZACC 11.4588 -11.4593 .

Measurements

Holotype (female) a = 13.03, b = 8.53, c = 5.27, V % = 50.51, total length = 2.475, maximum body width = 0.190, corpus length = 0.220, diameter of basal bulb = 0.083, total length of oesophagus = 0.290, nerve ring to anterior end = 0.133, excretory pore to anterior end = 0.243, vulva to posterior end = 1.225, tail length = 0.470, eggs = 0.100 -0.110 × 0.080 -0.085 (0.105 ± 0.005 × 0.083 ± 0.003 n = 3).

Paratypes (females) (n = 7) a = 11.35-14.12 (12.40 ± 0.89 n = 7), b = 8.89-12.50 (10.39 ± 1.65 n = 4), c = 4.80-7.99 (5.83 ± 1.07 n = 7), V % = 44.35-50.46 (48.43 ± 2.20 n = 7), total length = 2.400 -2.875 (2.754 ± 0.169 n = 7) , maximum body width = 0.170 -0.240 (0.224 ± 0.025 n = 7), corpus length = 0.180 -0.240 (0.205 ± 0.026 n = 4), diameter of basal bulb = 0.078 -0.103 (0.091 ± 0.009 n = 7), total length of oesophagus = 0.230 -0.310 (0.265 ± 0.034 n = 4), nerve ring to anterior end = 0.103 -0.135 (0.114 ± 0.015 n = 4), excretory pore to anterior end = 0.158 -0.270 (0.200 ± 0.041 n = 6), vulva to posterior end = 1.225 -1.600 (1.413 ± 0.123 n = 6), tail length = 0.360 -0.550 (0.481 ± 0.062 n = 7), eggs = 0.078 -0.105 × 0.070 -0.088 (0.097 ± 0.007 × 0.076 ± 0.004 n = 12).

Paratypes (males) (n = 6) a = 10.62-12.05 (11.02 ± 0.53 n = 6), b = 8.53-9.37 (8.92 ± 0.36 n = 4), c = 5.74-7.60 (6.47 ± 0.84 n = 6), total length = 2.160 -2.530 (2.315 ± 0.143 n = 6), maximum body width = 0.200 -0.220 (0.210 ± 0.006 n = 6), corpus length = 0.195 -0.213 (0.203 ± 0.008 n = 4), diameter of basal bulb = 0.073 -0.090 (0.081 ± 0.006 n = 6), total length of oesophagus = 0.240 -0.270 (0.258 ± 0.013 n = 4), nerve ring to anterior end = 0.100 -0.125 (0.118 ± 0.012 n = 4), excretory pore to anterior end = 0.190 -0.213 (0.201 ± 0.011 n = 5), tail length = 0.290 -0.430 (0.363 ± 0.056 n = 6), spicule length (on chord) = 0.133 -0.183 (0.159 ± 0.017 n = 6) .

Description

General: Cephalic extremity formed by a cephalic cap followed by a cephalic collar slightly umbelliform. Cephalic cap circular in en face view, bearing four mammiform papillae, two sub-ventral and two sub-dorsal. Amphids sub-dorsal, located in the junction of cap and cephalic collar, their diameter ca. 1.5 times larger than the papillae. Oral opening triangular, dorsal and ventral sectors equally developed, each bearing a median, rounded, cuticular projection. Cuticle with fine transverse striations, ca. 8 µm wide from the cephalic region to the base of tail; the striae are interrupted on both sides of body. Cervical region with large, fine, numerous microtricha, from the base of the cephalic cap to the first portion of the intestine. Microtricha near the cephalic collar ca. 30 µm length. Anterior part of oesophagus with three triangular jaw-like cuticular plates, one dorsal and two sub-ventral. Cuticular plate margins softly serrated, bearing six large triangular teeth. Teeth of opposite plates interlocking. Oesophagus with a muscular, clavate, comparatively short corpus with the anterior end expanded. A row of rounded, brown cells surrounding the corpus at base of its anterior expansion. Isthmus only appreciable as a constriction between the corpus and basal bulb. Basal bulb muscular, sub-spherical, anchored to body wall by muscles attached to its equatorial region, valve plate well developed. Intestine simple, sub-rectilinear. Nerve ring in the midpoint of the corpus. Excretory pore located in the base of corpus, near the junction of the basal bulb. Three short, rounded cardia extending from the base of basal bulb into the intestine.

Female: Type 4 genital tract after Adamson, 1987. Vulva not prominent, slightly displaced to posterior half of body. Vagina short, anteriorly directed, leading into a well developed, comparatively short and finewalled diverticulum. Two ovaries reflexed, arranged as a didelphic-amphidelphic genital system. Both uteri converge in a common duct that leads into the distal part of diverticulum. Eggs comparatively large, ellipsoidal, shell fine and smooth. A number of 4- 18 eggs at a time in the uteri. Tail conical, subulate, comparatively long, ending in a fine tip.

Male: Body length slightly shorter than female. Monorchic. Spicules moderately arcuate, slender, isomorphic and isometric. Spicules capitulum barely developed, distal tips pointed, covered by cuticular velae, shafts sculptured with irregular punctures on their surfaces. Posterior end of body ventrally curved. Tail base conical, becoming finer towards its apical point- ed tip. Tail dorsally elbowed at its narrowing point. Nineteen copulatory papillae. Pre-cloacal papillae arranged as a single median papilla near the anterior lip of cloaca, flanked by a pair of sub-ventral papillae at same level; three pairs equidistant (the distance between them similar to the distance between the median papilla and the first of such pairs); two pairs of papillae becoming more sub-lateral towards the anteriormost part. Some specimens present a seventh pre-cloacal pair of papillae more lateral and slightly equidistant from the sixth and fifth pairs. Post-cloacal papillae sub-ventral, comprising a first pair near the posterior lip of cloaca (at a distance of cloaca similar to the single median papilla) and two pairs just before the tail elbowing.

Type locality: La Isabelica, La Gran Piedra, Santiago de Cuba province, Cuba.

Type host: Nesobolus piedra Pérez-Asso, 1996 ( Diplopoda: Spirobolida : Rhinocricidae ).

Site: Hind gut.

Etymology: Specific epithet refers to the genus of the type host: Nesobolus .

Differential diagnosis

Rhigonema nesoboli sp. nov. is characterized by the body length of both sexes; the shape of the cephalic end; the form and extension of the microtricha; the form of the tail in both sexes; the genital tract of Type 4 (first Cuban species of the genus with such type of genital system); the number and arrangement of copulatory papillae and the form of the spicules.

Rhigonema villosum Hunt, 1995 is the closer species in the genus by having similar shape of the cephalic end, form and extension of the microtricha and shape of spicules. Differs from R. nesoboli sp. nov. by the number and arrangement of the copulatory papillae: 27 to 31 arranged as nine to eleven pre-cloacal pairs and four post-cloacal, plus a single median pre-cloacal papilla. The new species present 19 to 21 papillae: six or seven pre-cloacal pairs, three post-cloacal, and the single median pre-cloacal papilla. Both sexes of R. villosum are larger (total length of females 3.610 -5.850 vs. 2.400 -2.875; total length of males 2.570 -4.410 vs. 2.160 -2.530) ( Hunt, 1995).

Rhigonema licinacanthum Hunt & Moore, 1999 resembles R. nesoboli sp. nov. by the shape of the tail in both sexes and the spicules in males. It can be segregated by the upwardly bent microtricha vs. that backwardly directed of R. nesoboli sp. nov. and the number of copulatory papillae in males: 23 to 27 vs. 19 to 21. In R. licinacanthum , the duct joint to vaginal diverticulum is at its basal part, near the junction with the vagina (Hunt & Moore, 1999). On the other hand, in R. nesoboli sp. nov. the duct joint to diverticulum is at its distal part. Females and males of R. licinacanthum are larger (total length of females 5.340 -6.160 vs. 2.400 -2.875; total length of males 4.420 -5.340 vs. 2.160 -2.530) and the tails are comparatively longer (c of females = 3.50-4.20 vs. 4.80-7.99; c of males = 4.20-4.90 vs. 5.74-7.60).

Rhigonema thysanophora Crites, 1965 presents a similar tail shape and form, as well as extension of microtricha (long, fine and abundant, extending to the first portion of intestine) to those of R. nesoboli sp. nov. It differs by the shape of spicules, robust vs. slender in R. nesoboli sp. nov. The females of R. thysanophora are longer (3.010 -4.040 vs. 2.400 -2.875), but their tails are comparatively shorter (c = 13.68-16.83 vs. 4.80-7.99). The vulva is slightly displaced forward in R. nesoboli sp. nov. (V% = 44.35-50.46 vs. 53.00-56.00). Despite its longer body, the eggs of R. thysanophora are shorter than those of R. nesoboli sp. nov. (0.060 -0.070 × 0.048 -0.053 vs. 0.078 -0.105 × 0.070 -0.088) ( Crites, 1965).

The males of R. longecaudatum Dollfus, 1952 present an elbowing in the tail, as in R. nesoboli sp. nov. They differ by having very short microtricha, not surpassing the level of the oesophagus ( Dollfus, 1952). The spicules of R. longecaudatum are more curved and robust than in R. nesoboli sp. nov. Moreover, females and males of R. longecaudatum are longer (3.500 -3.800 vs. 2.400 -2.875) and present a notably shorter tail (c = 112.67-14.00 vs. 4.80-7.99). As occurs in females, males are also longer (2.900 -3.000 vs. 2.160 -2.530), with shorter tail (c = 15.00-15.68 vs. 5.74-7.60).

Rhigonema nesoboli sp. nov. differs from R. critesi Ramírez, 1974 ; R. nigella Dollfus, 1964 ; R. alvarengai Travassos & Kloss, 1960 ; R. carlosi Adamson, 1987 ; R. infecta (Leidy, 1849) and R. truncatum Artigas, 1926 by the shape of the cephalic collar, umbelliform in the Cuban species vs. rounded in the others. The tail of R. nesoboli sp. nov. is long and filiform in opposition to the very short, conical tail of the taxa men- tioned above. Spicules of males of the present species are comparatively slender and less arcuate vs. the arcuate of R. critesi , R. nigella and R. alvarengai (Travassos & Kloss, 1960; Dollfus, 1964; Ramírez, 1974), and the robust of R. carlosi , R. infecta and R. truncatum ( Artigas, 1926; Adamson, 1987). In addition, R. nesoboli sp. nov. can be segregated by the shape and extension of the microtricha.

Rhigonema nesoboli sp. nov. can be differentiated from R. pinguilabellum Hunt, 1981 ; R. pilosum Hunt, 1998 ; R. arawakae Hunt, 1999 ; R. caribae Hunt, 1999 and R. selvatica Tantalean & Altmamm, 1987 by the shape and length of the tail in males: longer and elbowed vs. short, from conical to slightly subulate in those species ( Hunt, 1981; Tantalean & Altmamm, 1987; Hunt, 1998, 1999a). Rhigonema nesoboli sp. nov. also differs from R. pilosum and R. selvatica by the shape of spicules of males: slender vs. robust.

Males of R. lanceacauda Hunt, 1981 ; R. flabellifer Hunt, 1999 ; R. tomentosum Hunt, 1995 and R. golovatchi Hunt, 1999 present the tail long, subulate and lacking in the characteristic elbowing of R. nesoboli sp. nov. ( Hunt, 1981, 1995, 1999 b) They also differ by the shape of spicules, slender, distally pointed and less curved in R. nesoboli sp. nov., in opposition to arcuate and robust in R. lanceacauda and R. flabellifer . Spicules of R. tomentosum are also slen- der, but notably arcuate. The microtricha of R. nesoboli sp. nov. are well developed, long, fine, their tips backwardly directed; unlike R. lanceacauda , R. flabellifer and R. tomentosum with densely distributed microtricha, their tips reflexed. Moreover, R. golovatchi possesses microtricha with a woolly appearance: quite dense and minute ( Hunt, 1999 b).

Rhigonema acrulocantha Hunt, 1995 resembles the new species by the shape of the tail and spicules, but differs by presenting curved, well developed spines, from the cephalic end to the tail ( Hunt, 1995). Such feature is unique among the species of this genus.

The other species with reproductive system of Type 4 are R. africanum Dollfus, 1964 , considered specie inquirendae and R. subtruncatum Dollfus, 1964 , synonym of R. truncatum (Van Waerebeke, 1984; Hunt, 1996).

Figures

FIGURE 1: Rhigonema nesoboli sp. nov. Female. A. Oesophageal region, lateral view. B. Cephalic end, internal view. C. Tail, lateral view. D. Vaginal region and diverticulum. E. Habitus, ventrolateral view.

FIGURE 2: Rhigonema nesoboli sp. nov. Male. A. Habitus, lateral view. B. Tail, lateral view. C. Tail, ventral view. D. Spicule

FIGURE 3: Rhigonema nesoboli sp. nov. Female. SEM images. A. Cephalic end, dorsolateral view. B. Cephalic end, en face view. C. Microtricha. D. Cuticular striae. Scale bars: A. 0.04 mm; B. 0.02 mm; C. 0.05 mm; D. 0.1 mm.