Macrostomum tuba Graff, 1882

Reyes, Jhoe & Brusa, Francisco, 2017, Species of Macrostomum (Macrostomorpha: Macrostomidae) from the coastal region of Lima, Peru, with comments on M. rostratum Papi, 1951, Zootaxa 4362 (2) : -

Macrostomum tuba Graff, 1882

Synonyms: Macrostomum bulbostylum Kepner & Stiff, 1932 Macrostomum gigas Okugawa, 1930

Macrostomum tuba bulbostylum Ferguson & Jones, 1940 Macrostomum tuba gigas Okugawa, 1930

Macrostomum tubum Hyman, 1936

Localities. The specimens were found in the sampling sites coded as CR-4 (11°44’1.8’’S; 76°58’19.56’’W), CR-5 (11°44’4.38’’S; 76°58’20.52’’W) and CR-6 (11°43’30.9’’S; 76°57’54.1’’W) ( Figure 1 , Table 1) in the Chillón River in Lima.

Other localities in Peru. The species has been previously found at the Pacaya-Samiria National Reserve in Loreto region: “cocha” Zapote and the “caño” Yarina (5°20’16’’S; 74°29’40’’W) ( Noreña et al. 2006).

Other localities in the world. The species has a worldwide cosmopolitan distribution ( Adami et al. 2016; Ferguson 1940; Gamo & Leal-Zanchet 2004; Hyman 1955; Marcus 1946; Noreña et al. 2003; Papi 1951; Wang et al. 2004; Young 1976).

Studied material. Eight specimens observed alive (squash method) and eight (MUSM 3406–3413) specimens fixed in polyvinyl–lactophenol.

Description. Adult specimens exhibit whitish–orange body coloration when observed in reflected light. The body is 2.2–2.7 mm long and 0.8–1.2 mm wide. The anterior region is rounded in shape, whereas the posterior region is spatula–shaped when the specimen is attached to the substrate ( Figure 5A ).

Male reproductive system: Two ellipsoid–shaped testes at the sides of the body, approximately at the beginning of the intestine. A thin-walled false seminal vesicle stores sperm and continues into a thick-walled, muscular seminal vesicle through a thin and short intervesicular duct. The seminal vesicle is about a quarter of the size of the false seminal vesicle. Distally, the seminal vesicle connects to the prostate vesicle. Within the prostate vesicle, granulations are observed. These are grouped in small and long sacs that enter the stylet proximally ( Figure 5B ). The stylet is a slightly-curved, long and slender tube ( Figure 5C ). The stylet is 206.9 µm long (162.5–291.5 µm; n = 8; sd = 46.7), and progressively narrows from the base, which is 10.2 µm wide (7.8–15.3 µm; n = 6; sd = 2.6), to the distal opening, which is 2.8 µm wide (2.2–5 µm; n = 8; sd = 0.9). The stylet wall is thickened in its distal portion, which is typical for this species ( Figure 5C ).

The female reproductive system is typical for the genus. The ovaries are located in the third part of body, arranged lateroventrally to the intestine ( Figure 5A ). The female genital atrium is anterior to the false seminal vesicle. In some adult specimens, egg formation was observed in the atrium.

Remarks. The most remarkable feature of M. tuba is the penis stylet, although the diameter of the base, size of shaft and diameter of the distal opening vary according to the region and habitat ( Hyman 1936; Ferguson 1939, 1940; Papi 1951; Young 1976). The shape of the distal region of the stylet, with thickened walls, remains constant ( Wang et al. 2004) ( Figure 5C ), making easily the recognition of the species. Also, the stylet and body length in M. tuba are variable; smaller body lengths usually have a straight and not slightly curved stylet, as observed in larger specimens (greater than 3 mm) ( Young 1976; Ferguson 1939, 1940; Hyman 1936; Bois-Reymond Marcus 1957). These characteristics were observed in the specimens found in the Chillón River.

M. tuba was associated with the same vegetation and physicochemical parameters as M. quiritium ( Table 2).

Figures

FIGURE 1. Sample sites where species of Macrostomum were found. A, M. quiritium and M.tuba in Chillón River (sites 4, 5 and 6). B, M. rostratum in Humedales de Ventanilla (sites 1, 2 and 3).

FIGURE5. Macrostomum tuba Graff,1882.A, Dorsalview of a mature specimen;B, Posterior body region withdetails of the copulatory organs; C, Detail of the penis stylet.