The adult musculature of two pseudostomid species reveals unique patterns for flatworms (Platyhelminthes, Prolecithophora)

Abstract

We analyzed the adult musculature of two prolecithophoran species, Cylindrostoma monotrochum (von Graff, 1882) and Monoophorum striatum (von Graff, 1878) using a phalloidin‐rhodamine technique. As in all rhabdithophoran flatworms, the body‐wall musculature consisted of three muscle layers: on the outer side was a layer of circular muscle fibers and on the inner side was a layer of longitudinal muscle fibers; between them were two different types of diagonally orientated fibers, which is unusual for flatworms. The musculature of the pharynx consisted of a basket‐shaped grid of thin longitudinal and circular fibers. Thick anchoring muscle fibers forming a petal‐like shape connected the proximal parts of the pharynx with the body‐wall musculature. Male genital organs consisted of paired seminal vesicles, a granular vesicle, and an invaginated penis. Peculiar ring‐shaped muscles were only found in M. striatum, predominantly in the anterior body part. In the same species, seminal vesicles and penis only had circular musculature, while in C. monotrochum also longitudinal musculature was found in these organs. Female genital organs were only present in M. striatum, where we characterized a vagina interna, and a bursa seminalis. Transverse, crossover, and dorsoventral muscle fibers were lacking in the middle of the body and greatly varied in number and position in both species.

Do Not Lose Your Head over the Unequal Regeneration Capacity in Prolecithophoran Flatworms

“…When amputated in the middle of the body the restored pharynx had a diameter of ca. 99 +/− 7.5 µm, while the original size is ca 150 +/− 6.4 μm [ 52 ].…”

The organization of the muscle system of the causative agent of dicrocoeliosis, Dicrocoelium dendriticum

“…Transverse muscle fibers have also been identified in cestodes (Mair, Maule, Shaw, & Halton, 1998). Some authors noted the presence of transverse muscles in other flatworms; for example, Grosbusch et al (2019) identified bundles they called “transverse” in the posterior and anterior body regions of two prolecithophorans (Platyhelminthes), Cylindrostoma monotrochum and Monoophorum striatum . In the free‐living turbellarian Dugesia japonica (Platyhelminthes), transverse muscle fibers were also observed distributed across the body (Orii et al, 2002).…”

The serotonergic nervous system of prolecithophorans shows a closer similarity to fecampiids than to triclads (Platyhelminthes)

“…We collected adult specimens of all six prolecithophoran species [ Cylindrostoma fingalianum (Claparède, 1861); Cylindrostoma monotrochum (von Graff, 1882); Monoophorum striatum (Graff, 1878); Plagiostomum koreni Jensen, 187 8 ; Acmostomum dioicum Metschnikoff, 1865; Vorticeros auriculatum (Müller, 1784)] from brown algae in the port of Punat, Krk, Croatia (45°01′23”N 14°37′41″E) in March 2016, October 2016, 2017, May 2018, and in October 2019. The extraction and maintenance of the animals were made according to Grosbusch et al (2019).…”

“…For staining, nine adult C. fingalianum (Figure 1(a)), five adult C. monotrochum (Figure 2(a)), 12 adult M. striatum (Figure 3(a)), six adult P. koreni (Figure 4(a)), 14 adult A. dioicum (Figure 5(a)), and seven adult V. auriculatum (Figure 6(a)) were used. Cylindrostoma monotrochum and M. striatum were stained according to Grosbusch et al (2019). Four individuals of V. auriculatum were stored at −20°C before staining; two in ethanol and two in aceton.…”

“…Specimens were embedded in Technovit resin and semi‐thin sectioned at 3 μm thickness using a microtome (Reichert‐Jung Autocut 2040) and stained using a standard hematoxylin & eosin (H&E) protocol (see Grosbusch et al, 2019 for details).…”