Rhopalias oochi, Lopez-Caballero, Jorge, Mata-Lopez, Rosario & Leon, Gerardo Perez-Ponce de, 2019

Lopez-Caballero, Jorge, Mata-Lopez, Rosario & Leon, Gerardo Perez-Ponce de, 2019, Molecular data reveal a new species of Rhopalias Stiles & Hassall, 1898 (Digenea, Echinostomatidae) in the Common opossum, Didelphismarsupialis L. (Mammalia, Didelphidae) in the Yucatan Peninsula, Mexico, ZooKeys 854, pp. 145-163 : 151-152

Rhopalias oochi sp. nov. Figures 3 A–D, 4 A, D, E, 5A, D

Synonym.

Rhopalias coronatus of Acosta-Virgen et al. (2015). Specimens deposited in the CNHE (9504).

Type host.

Didelphis marsupialis Linnaeus, Common opossum ( Mammalia: Didelphidae ).

Type locality.

Rancho Hobonil, Tzucacab, Yucatán state, Mexico (20°00'58"N, 89°01'12"W).

Site in host.

Small intestine.

Prevalence and intesity of infection.

100% (1 of 1 opossum ), infected with 15 trematodes.

Type specimens.

Holotype: CNHE 9504; paratypes: CNHE 10926 (3 specimens) and hologenophores CNHE 11069 (4 specimens).

Etymology.

The specific epithet refers to the common name of the host where the new species was found. In the Mayan language, “ooch” means opossum .

Description.

Based on 11 adult specimens (including 4 hologenophores). Measurements are given in Table 3. Trematodes with a long body, forebody concave, wider than hindbody, with a pair of armed retractile tentacles with 4-7 spines (Fig. 3A, B, C). Tegument covered with spines reaching posterior end of body (Fig. 4A). Tegument spines U-shaped, with distal tip pectinated (Fig. 4D, E). Oral and flanking spines present (Figs 3C, 5A, 5D). Muscular sacs long, reaching far beyond posterior margin of pharynx, and may or may not reach the anterior margin of ventral sucker (Fig. 3A, B). Oral sucker subterminal, rounded, well-developed, short prepharynx, pharynx muscular, and relatively long oesophagus; caecal bifurcation at short distance anterior to genital pore (Fig. 3B); long caeca extending to the posterior end of body (Fig. 3A). Ventral sucker muscular and subspherical, in the first third of body, larger than oral sucker (Figs 3A, B, 4A). Testes two, elongated, in tandem, contiguous, no overlapped, located in mid-body; anterior testis shorter than posterior testis (Fig. 3B). Cirrus sac long, claviform, containing a well-developed prostate complex and seminal vesicle, extending beyond ventral sucker and terminating near anterior border of ovary. Genital pore between ventral sucker and caecal bifurcation. Ovary slightly oval, postacetabular, pretesticular. Uterus intercaecal, between ovary and genital pore. Metraterm long (Fig. 4D). Vitelline follicles in lateral fields, beginning at mid-level between ventral sucker and ovary, ending at posterior end. Gravid specimens with few eggs, oval-shaped, operculated; embryonated eggs with thin shell.

Remarks.

The genus Rhopalias currently contains six species as parasites of New World marsupials ( Haverkost and Gardner 2008), i.e., Rhopalias coronatus , the type species; Rhopalias horridus (Diesing, 1850) Stiles and Hassall 1898; Rhopalias baculifer Braun, 1901; Rhopalias macracanthus Chandler, 1932; Rhopalias caballeroi Kifune & Uyema, 1982; and Rhopalias caucensis Rivillas, Caro, Carvajal & Vélez, 2004. Rhopalias oochi sp. nov. represents the seventh described species and is readily distinguished from five of the congeneric species, excepting R. coronatus by having tentacle sacs extending far beyond the posterior margin of pharynx. In their detailed morphological revision of the genus Rhopalias , Haverkost and Gardner (2008) provided a key to species of the genus and found that this character is reliable to distinguish between two groups of species. In R. horridus , the tentacle sacs surpass the posterior margin of pharynx to reach the mid-level of oesophagus; however, they never extend beyond the caecal bifurcation. In R. oochi sp. nov. the tentacle sacs extend to reach the anterior margin of ventral sucker. Rhopalias horridus further differ from the new species, and the remaining congeners by the large number of tentacle spines (> 30) (see key in Haverkost and Gardner 2008). The new species most closely resembles the type species, R. coronatus ; in fact the specimens upon which the description of the new species is based were originally recorded as R. coronatus (see Acosta-Virgen et al. 2015). Genetic data revealed that they might actually represent a different species. In R. coronatus as in the new species tentacle sacs extend far beyond the posterior border of pharynx; in R. coronatus , both sacs usually surpass the anterior border of ventral sucker (although our observation of numerous voucher specimens indicate that the extension is variable among individuals); in the new species, the tentacle sacs consistently extend to almost reach the anterior border of ventral sucker, but never surpass it. Additionally, R. coronatus differ from the new species by having larger oral spines (at least four times larger), and by the distribution of vitelline follicles. In R. coronatus follicles extend between the posterior end of body and the posterior border of ventral sucker; instead, in R. oochi sp. nov. vitelline follicles do not reach the posterior end of body, and in the forebody, they reach the mid-level of cirrus sac. Morphometrically, most measurements are clearly overlapped between the new species and R. coronatus (except in oral spines size). We observed and measured 21 individuals of R. coronatus deposited at the CNHE. Our measurements, and those reported in other studies (see Table 3) indicate that R. coronatus is morphometrically quite variable. Furthermore, SEM study of the ultrastructure of the body surface provided additional evidence to distinguish the new species from R. coronatus and R. macracanthus ; for these two species we collected specimens and some were fixed for a comparative SEM study (Fig. 4). In the three species body spines are denser in the forebody; however, the extension, size, and shape of spines clearly distinguish the three species. In R. oochi sp. nov., spines are robust and pectinate and they extend along the body almost to the posterior end (Fig. 4A, D, E); meanwhile, in R. coronatus spines are distributed to the mid-level of hindbody and are entire and tongue-shaped (Fig. 4B, F, G) and in R. macracanthus , even though spines extend more posteriorly, they are not as robust as in the new species; spines in R. macracanthus are pectinate and arrow-shaped (Fig. 4C, H, I).