Macrostomum rostratum Papi, 1951

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 rostratum Papi, 1951

Synonyms: Macrostomum viride rostrata Papi, 1951 Macrostomum phytophilum Beklemischev, 1951 Macrostomum rostratus Ferguson, 1954

Localities. The specimens were found in the sampling sites coded as HV-1 (11°52’20.2’’S; 77°08’18.9’’W), HV-2 (11°52'15’’S; 77°08’16.4’’W) and HV-3 (11°52’30.8’’S; 77°08’42.5’’W) ( Figure 1 , Table 1) in Humedales de Ventanilla in Lima.

Other localities in the world. The species has been found in several countries around the world: Russia, Finland ( Luther 1960), Italy ( Papi 1951), United Kingdom, Ireland ( Young 2001), Spain ( Farías et al. 1995; Noreña et al. 2007), The Netherlands ( Tulp 1974), Kenya ( Young 1976) and Brazil ( Braccini & Leal-Zanchet 2013).

Studied material. Twenty-five specimens observed in vivo (squash preparations) and 28 (MUSM 3320–3346) specimens fixed in polyvinyl-lactophenol.

Description. Body usually whitish that turns to yellow–mustard ( Figure 2A ) when the intestinal contents ( Figures 2A ; 3C) reflect the light (algae, rotifers, ostracods and sometimes larvae of dipterans). The anterior part of the body is truncated, and widens to reach its maximum width at about 2/3 of the body length. The posterior end is spatula–shaped with a large number of adhesive papillae on its edge. The length of the body varies from 1.5 to 2 mm. The epidermis has locomotor cilia and longer sensory cilia throughout the body. Abundant rhabdites grouped in packs of seven to twelve rhabdites each and distributed mainly on the dorsal surface of the body. Cerebral ganglia paired and linked by a weak cerebral commissure. The ciliated mouth is located just behind the eyes. The pharynx simplex possesses a large quantity of thin pear-shaped glands ( Figures 2A–B ; 3A).

Male reproductive system: Oval, thin-walled testes latero-ventral in the mid-part of the body, flanking the intestine ( Figures 2C ; 3A). The seminal vesicle is bilobed and globular in shape, with thick walls and full of spermatozoa. When swimming, the anterior region of the seminal vesicle (anterior lobe) is positioned close to the left side and to the ventral surface of the body, while the posterior region (posterior lobe) is located in the dorsal position, slightly posterior to the anterior lobe and on the central body axis. Both lobes are separated by a constriction. The seminal vesicle continues at its distal end with the smaller prostatic vesicle, which immediately joins the proximal end of the stylet ( Figure 2A, E ). Digitiform prostate glands fill the prostate vesicle and the proximal region of the stylet. The stylet is a conical tube that is housed in a muscular tunica. Proximally, the stylet has a slightly crenellated base, which is 38.4 µm in length (26.8–49.8 µm; n = 27; sd = 6.8), whereas distally, its shaft is curved at an angle of ± 90° (with the curvature attenuated). The subterminal opening of the stylet is 9.6 µm long (7.4–12.7 µm; n = 22; sd = 1.5) and located on the concave side of the stylet ( Figures 2G ; 3D, E). The total length of the stylet (sensu Schockaert 2014) is 82.4 µm (70.4–92.5 µm; n = 18; sd = 6.6), whereas the total height of the stylet is 49.2 µm (37.3–59.6 µm; n = 26; sd = 5.7) ( Figures 2G ; 3D, E).

Spermatozoa consist of body and shaft ( Figures 2F ; 3F) and their total length is 31.9 µm (24.2–44.4 µm, n = 14; sd = 5.1).

Female reproductive system: Typical of the genus. The ovaries are located behind the middle of the body, and have brownish–yellow coloration. The female atrium is located posterior to the intestine, ventrally, and is surrounded by shell glands. The female atrium usually contains eggs in formation ( Figures 2A, D ; 3A).

Remarks. Based on the morphological characteristics observed, the individuals collected belong to the species with a hook-shaped stylet. The species of this group are characterized by a stylet with a broad base, a funnel-shaped shaft, and a pointed distal portion which is curved into a hook at an angle of ± 90°. The opening of the ejaculatory duct lies at the level of the stylet curvature, in the concave or convex portion ( Figures 2G ; 3E). In most species of this group ( M. appendiculatum Fabricius, 1826 , M. balticum Luther, 1947 , M. distinguendum Papi, 1951 , M. hystricinum Beklemischev, 1951 , M. hystrix Ørsted, 1843 , M. pusillum Ax, 1951 , M. romanicum Mack-Fira, 1968 , and M. sileciacum Kolasa, 1973 ), the general shape of the stylet is very similar, with the distal opening on the convex side of the curvature. However, in M. rostratum , the stylet opening occurs on the concave side.

Based principally on the copulatory apparatus, we here report M. rostratum Papi, 1951 for the first time in Peru. This species has been described for Europe and inhabits both brackish and freshwater environments ( Braccini & Leal-Zanchet 2013; Noreña et al. 2007; Papi 1951, 1959; Young 1976). The morphological characteristics of the specimens found in Humedales de Ventanilla are similar to those described by Papi (1951, 1959) and Luther (1960); however, there are some differences in the copulatory apparatus. The stylets of the specimens from Humedales de Ventanilla have the shape of a solid inverted cone, whereas those reported by Papi (1951, 1959) are slightly spiral- or “S”-shaped as is also the case in M. hystricinum . However, in the latter species, the distal opening is on the convex side of the stylet. In the specimens found in Humedales de Ventanilla, the distal opening is clearly seen as described by Papi (1959), while in the specimens reported by Papi (1951), this opening is not clearly stated.

The size of the stylets of the specimens found in Humedales de Ventanilla differs slightly from those recorded so far. In Europe, lengths of 67 µm ( Papi 1959), 52–60 µm ( Luther 1960), 63 µm ( Tulp 1974), 53 µm ( Young 1976) and 36–77 µm ( Heitkamp 1979) have been recorded, whereas the height of the stylet of the specimens studied here are similar to those found by the authors mentioned above. We thus infer that the stylet dimensions of this species are variable, as in other species of the genus. The morphology of the spermatozoa and stylet of M. rostratum suggests hypodermic insemination ( Schärer et al. 2011). However, new observations are needed to confirm this hypothesis.

In some occasions, M. rostratum was found with its intestinal content full of cladocerans ( Figure 3C ). Moreover, this species was associated with vegetation such as Cyperus sp., Arundo sp., Salicornia sp., Chara sp. and Typha domingensis Pers. ; the water temperature was 20.88 °C on average, the pH was 9.16 and the conductivity was 20 mS/cm ( 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).

FIGURE 2. Photographs of a live specimen of Macrostomum rostratum Papi, 1951. A, Dorsal view of a mature specimen; B, Detail of the anterior body region; C, Detail of the testes; D, Detail of the ovary; E, Posterior body region with details of the copulatory organs; F, Detail of four spermatozoa in different focal planes; G,Penis stylet.

FIGURE 3. Macrostomum rostratum Papi, 1951. A, Schematic reconstruction of the body; B, Detail of the male copulatory system; C, Specimen of M. rostratum with mainly microcrustaceans in the intestine; D–E, Schematic representation of the stylet with measurements taken; F, Detail of a spermatozoon.