Macrostomum quiritium Beklemischev, 1951

Reyes, Jhoe, Binow, Daniela, Vianna, Rogério T., Brusa, Francisco & Martins, Samantha E., 2021, Fig. 12. Majella pristis n in Periclimenaeus djiboutensis Bruce 1970, Zoological Studies 60 (22), pp. 1-33 : 10

Macrostomum quiritium Beklemischev, 1951 ( Fig. 3H–I )

Synonym: Macrostomum dongyuanensis Wang and Sun, 2015 .

Studied material: Twenty-two live individuals. Six individuals observed alive on squashed preparations. The remaining, whole-mounted stylets studied (MZUSP PL 2219–2234).

Localities: Site 1 (23/06/2018; 1/07/2019) and Site 3 (18/02/2019; 24/04/2019; 5/06/2019), associated with benthal and phytal microhabitats.

Description: Body 1671.3 ± 712 μm (1074.7– 3088.3 μm; n = 6) long and 383.5 ± 135 μm (194.1– 597.7 μm; n = 6) wide ( Fig. 3H ). Anterior region rounded in shape and the posterior end is spatula-shape. The female reproductive system is composed of ovaries and a female antrum. The male reproductive system presents anterior paired testes, false seminal vesicle, seminal vesicle, prostate vesicle, a penis stylet and a male gonopore. The slightly curved penis stylet, 150.8 ± 17.7 μm (118.9–172.2 μm; n = 17) long, is tube-shaped ( Fig. 3I ). The shaft narrows from the base, 18.9 ± 3.8 μm (12.4–27.2 μm; n = 17) width, to the distal opening, 4.9 ± 0.5 μm (4.1–6.4 μm; n = 17) width. The distal tip of the stylet ends in a very slight slope ( Fig. 3I ).

Taxonomic remarks: Our observations agree with descriptions for M. quiritium ( Kolasa 1973b; Sun et al. 2015; Adami et al. 2016; Reyes and Brusa 2017). However, individuals from the ESEC Taim have a longer penis stylet than those from the original description ( Kolasa 1973b); the same trait is followed for specimens reported for Peru ( Reyes and Brusa 2017) and Argentina ( Adami et al. 2016). Also, variations in the size of the penis stylet are observed when comparing the proximal base and the distal opening but are within the range of the species morphology. Although measurements of the penis stylet slightly differ from descriptions given for the Neotropical region ( Adami et al. 2016; Reyes and Brusa 2017), the morphology remains the same. Nevertheless, specimens from China are slightly longer ( Sun et al. 2015) (2639 ± 274.2 µm) when it comes to comparing body size. In addition, M. quiritium was not previously reported for Brazil, therefore it is recorded for the first time for the country and the third time for the Neotropical region. Sun et al. (2015) described the species Macrostomum dongyuanensis from China. However, a posterior morphological and molecular analyses demonstrated that M. dongyuanensis did not differ from M. quiritium ( Xin et al. 2019) . Therefore, M. dongyuanensis is a junior synonym of M. quiritium as Xin et al. (2019) stated.

Distribution: Widely distributed, the species occurs in Russia, Poland, Switzerland ( Schärer et al. 2011), China ( Sun et al. 2015; Xin et al. 2019), Argentina ( Adami et al. 2016), and Peru ( Reyes and Brusa 2017).

Figures

Fig. 3. Live specimens of Stenostomidae and Macrostomidae. (A–C) Stenostomum cf. pegephilum: (A) chain with two zooids, (B) schematic representation, (C) detail of the muscular pharynx. (D1–2) Stenostomum saliens: (D1) detail of the anterior region of the body and (D2) dorsal view of the habitus of a specimen. (E) Stenostomum simplex (scale bar not available). (F–G) Stenostomum tuberculosum: (F) individual with three zooids, (G) schematic representation. (H–I) Macrostomum quiritium: (H) dorsal view of a mature specimen, (I) detail of the penis stylet. (J) Macrostomum tuba, detail of the penis stylet.