Riggenbachiella, Alves, de Chambrier, Luque & Scholz in Press, 1999

Philippe Vieira Alves, Alain de Chambrier, José Luis Luque & Tomáš Scholz, 2017, Untangling convoluted taxonomy of Chambriella Rego, Chubb & Pavanelli, 1999 (Cestoda: Proteocephalidae), with erection of Riggenbachiella n. g. and the description of a new species from pimelodid catfishes in the Neotropical Region, Syst Parasitol 94, pp. 367-389 : 372-373

Riggenbachiella n. g.

Syn. Chambriella Rego, Chubb & Pavanelli, 1999 (pro parte)

Diagnosis

Proteocephalidae , Monticelliinae . Small-sized worms. Testes, ovary, vitelline follicles and uterus cortical.

Strobila acraspedote, with proglottides variable in shape and size. Scolex quadrilobed, quadrangular in apical view, wider than proliferative zone, with rounded to conical apex; metascolex absent. Suckers large, bi-loculate, with free posterior margin overlapping narrow proliferation zone, well delimited from scolex proper; loculi variable in shape and size.

Internal longitudinal musculature formed by small, sparsely distributed bundles of muscle fibres. Testes in one field. Cirrus-sac sigmoid, composed of three parts: large, chambered internal seminal vesicle, middle muscular part with sinuous ejaculatory duct followed by straight, short cirrus with inverted T-shaped ejaculatory duct in its proximal part. Genital pore pre-equatorial, irregularly alternating. Genital atrium present. Ovary bi-lobed, slightly follicular. Vagina anterior, exceptionally posterior to cirrus-sac, with short thickened portion surrounded by ring-like vaginal sphincter. Vitelline follicles arranged in two lateral bands. Uterine development type 2 according to de Chambrier et al. (2004). Parasites of pimelodid catfishes ( Siluriformes : Pimelodidae ) in the Neotropical Region. Type-species: Riggenbachiella amazonense n. sp.

Etymology: This name is given in honour of the late Emil E. Riggenbach, University of Basel, Switzerland, for his contribution to the systematics of proteocephalid cestodes at the end of the 19th Century. The name should be treated as femininum.

Remarks

The new genus is placed in the Monticelliinae because of the cortical position of the testes, ovary, vitelline follicles and uterus ( Rego, 1994). To date, the subfamily includes nine genera parasitising freshwater fishes in the Neotropical region, namely Ageneiella de Chambrier & Vaucher, 1999 ; Chambriella Rego, Chubb & Pavanelli, 1999 ; Choanoscolex La Rue, 1911 ; Goezeella Fuhrmann, 1916 ; Manaosia Woodland, 1935 ; Monticellia La Rue, 1911 ; Regoella Arredondo, de Chambrier & Gil de Pertierra, 2013 ; Spasskyellina Freze, 1965 ; and Spatulifer Woodland, 1934 .

Riggenbachiella n. g. can be readily distinguished from all the above-mentioned taxa by the unique morphology of the cirrus-sac, which is sigmoid and composed of three parts: a voluminous, chambered internal seminal vesicle, a muscular middle part with a sinuous ejaculatory duct, and a straight, short cirrus with an inverted T-shaped ejaculatory duct in its proximal part (see Figs. 4B–F , 5B–D).

The new genus can be further differentiated from all but three monticelliine genera by having biloculate suckers instead of uni-loculate ones present in Choanoscolex , Manaosia , Monticellia , Regoella , Spasskyellina and Spatulifer . Riggenbachiella n. g. differs from Ageneiella and Goezeella , which also have bi-loculate suckers, in several features, such as the absence of a metascolex (present in Goezeella ), the different development of the inner longitudinal musculature (well-developed in Goezeella and Ageneiella ) and unequal extension of the uterine diverticula (branches penetrate into the medulla, sometimes reaching the dorsal cortex in Ageneiella ).

Another genus with bi-loculate suckers, Chambriella (syn. Lenhataenia , see above), differs from Riggenbachiella n. g. by the morphology of the cirrussac (it has a ‘typical’ structure with a simple internal sperm duct forming several coils, not being enlarged to form an internal seminal vesicle; see Fig. 3B, C in the present paper and figure 42 in de Chambrier & Scholz, 2008).

Figures

Fig. 3 Chambriella megacephala (Woodland, 1934) ex Zungaro jahu. A, Scolex, apical view (paratype of C. agostinhoi, CHIOC 32820 c); B, Terminal genitalia, ventral view (holotype of C. agostinhoi, CHIOC 32820 a); C, Terminal genitalia, dorsal view (MHNH- PLAT 22025); D, E, Cross-sections at anterior and cirrus-sac level of proglottides, respectively (MHNH-PLAT 19546); F, Eggs drawn in distilled water (MHNH-PLAT 20768). Abbreviations: al, anterior sucker loculus; ci, cirrus; cs, cirrus-sac; do, dorsal osmoregulatory canal; ed, ejaculatory duct; em, bi-layered embryophore; lm, internal longitudinal musculature; oe, outer envelope; on, oncosphere; pl, posterior sucker loculus; st, subtegumental muscle fibres; su, subtegumental cells; te, testes; tg, tegument; ut, uterus; va, vas deferens; vi, vitelline follicles; vo, ventral osmoregulatory canal; vs, vaginal sphincter. Scale-bars: A, D, E, 200 l m; B, C, 100 l m; F, 20 l m

b Fig. 4 Riggenbachiella amazonense n. sp. ex Phractocephalus hemioliopterus (A, C, E, H, I), Sorubimichthys planiceps (typehost; B, D, F, J) and Zungaro zungaro (G). A, Scolex, dorsoventral view (MHNH-PLAT 67054); B, Pregravid proglottis, ventral view (IPCAS C- 749); C, Mature proglottis, ventral view (MHNH-PLAT 79199); D, Terminal genitalia, ventral view (IPCAS C- 749); E, F, Cross-sections at level of cirrus-sac, detailed in F (MHNH-PLAT 22005, 94096); G, Cross-section, detail at posterior level of proglottis (MHNH-PLAT 19544); H, I, Cross-sections, detail at posterior and ovary levels of proglottides, respectively (MHNH-PLAT 22005); J, Eggs drawn from whole-mounted specimen (MHNH-PLAT 70835). Abbreviations: al, anterior sucker loculus; ci, cirrus; cs, cirrus-sac; do, dorsal osmoregulatory canal; em, bi-layered embryophore; gc, glandular cells; idc, internal sperm duct chambers; lm, internal longitudinal musculature; mg, Mehlis’ gland; on, oncosphere; ov, ovary; pl, posterior sucker loculus; te, testes; ut, uterus; va, vas deferens; vi, vitelline follicles; vo, ventral osmoregulatory canal; vs, vaginal sphincter; vt, vitelloduct. Scale-bars: A, B, C, 500 l m; D, F, 100 l m; E, 250 l m; G, H, I, 50 l m; J, 20 l m