Pseudogeoplana arpi (Schirch, 1929)

Silva, Marcos Santos & Carbayo, Fernando, 2020, X-ray microcomputed tomography applied to the taxonomic study of rare material: redescriptions of seven of Schirch's Brazilian species of land planarians (Geoplanidae, Platyhelminthes), ZooKeys 910, pp. 1-42 : 1

Pseudogeoplana arpi (Schirch, 1929) Figures 16 , 17 , 18

Geoplana arpi Schirch, 1929: 33. Type Locality: Baixo Guandu, Espírito Santo, Brazil

Geoplana arpi : Ogren and Kawakatsu 1990: 113.

Pseudogeoplana arpi : Carbayo et al. 2013: 524.

Material examined.

Type material. Two syntypes available, collected by P. Schirch in 1917 at Baixo Guandu (former Maylasky), State of Espírito Santo, Brazil. We received them on loan in 70 % ethanol with label reading 8914. Three dimensional (3D) images and virtual sections of syntype MNRJ 206A were obtained by microcomputed tomography. Parts of body of syntype MNRJ 8914B were histologically sectioned as follows. Syntype MNRJ 207B: Transverse sections of anterior extremity on 20 slides; horizontal sections of a region posterior to anterior extremity, 4.5 mm long on 73 slides; transverse sections of pre-pharygeal region on 50 slides; sagittal sections of pharynx on 135 slides; remaining part of body preserved in 80 % ethanol.

External aspect.

Syntype 206 is 160 mm long, 10 mm wide, and ~2 mm high (Fig. 16A, C ); syntype 207, 70 mm, ~8 mm, and ~2 mm (Fig. 16D ), respectively. Elongated body, with margins approximately parallel; anterior extremity pointed, posterior rounded, body sides rounded. Dorsum convex, ventral side flat, convex on some portions of median region most probably the result of contraction at moment of fixation. Ground color of dorsum clay brown with irregular faded areas visible to naked eye (Fig. 16A, D ). Ventral side grey beige.

Eyes monobolate, surround anterior extremity of the body (Fig. 17A ) and are distributed evenly dorsolaterally along the entire body length. Sensory pits are simple invaginations 15 µm deep, located ventro-marginally in a single row (Fig. 17B ) that contours the anterior extremity and extends posteriorly at least ~4 mm (or 7 % of the body length). Relative position of the mouth: body length, ~55 %. Relative position of incipient gonopore: body length, ~70 % in syntype 207.

Internal morphology.

Epithelium ciliated in anterior extremity, dorsally and ventrally; otherwise only ciliated on the ventral surface. Creeping sole comprising 92 % body width. In pre-pharyngeal region, abundant rhabditogen cells and glands producing erythrophil granules pierce dorsal and marginal epidermis; glands producing amorphous orangish-to-reddish secretion pierce marginal and dorsal epidermis. Ventral epithelium pierced by glands producing fine erythrophil granules. Glandular margin absent (Fig. 17C ).

Cutaneous musculature comprises three layers, namely a subepithelial circular layer, followed by a diagonal layer of decussate fibers, and then a well-developed innermost longitudinal layer. Muscle fibers of the longitudinal layer (45 µm thick dorsally; 75 µm thick ventrally) arranged into bundles with 13-46 fibers each. Cutaneous musculature thickness relative to body height in the pre-pharyngeal region, 10 % (Fig. 17C ). No muscle modifications in anterior extremity (Fig. 17A, B ). Three parenchymal muscle layers present: a dorsal layer (10 µm thick) of decussate fibers, a supraintestinal layer (100 µm thick) with transverse fibers, and a poorly developed subintestinal layer (100 µm thick) of transverse fibers (Fig. 17D ). Ventral nerve plate well developed.

Mouth situated at a distance from the root of the pharynx equivalent to 32 %-47 % of pharyngeal pocket length (syntypes 206 and 207, respectively). Pharynx cylindrical, tending to bell-shaped (Fig. 18A, B ), occupying anterior half of the pharyngeal pocket. Esophagus absent. Free surface of outer pharyngeal epithelium undulated and ciliated, underlain by a subepithelial longitudinal muscle (8 µm thick) and followed by a circular muscle (50 µm thick). Inner pharyngeal musculature consisting of a subepithelial circular muscle (25 µm thick), followed by a longitudinal muscle (5 µm).

Testes poorly developed, rounded, ~100 µm in diameter, with no developed sperm. They are dorsally located among fibers of the supraintestinal transverse parenchymal muscle layer. Anteriormost testes at a distance from the anterior extremity of the body equivalent to 26 % of body length; posteriormost testes, 36 %, i.e., anterior to pharyngeal pocket (Fig. 17D ).

Copulatory apparatus very poorly developed (Fig. 18C, D ). It occupies the ventral 2/3rd of the body height. Each of the paired sperm ducts opens into the proximal region of the bifurcate prostatic vesicle. This vesicle is intrabulbar and consists of an unpaired region running ventro-posteriorly inside a weakly developed penis bulb. Prostatic vesicle opens into a flat cavity, 35 µm high and 250 µm wide, delimited by a dorsal fold and a ventral fold. These folds project posteriorly from the anterior wall of the male atrium, forming a structure resembling a short, conical penis papilla. Ejaculatory duct not observed. Male atrium forms a 1.5 mm long closed cavity, i.e., it does not open to the outside of the body through an eventual gonopore canal. The atrium is narrower posteriorly and there is no differentiation between the male and female atria. The atrial epithelium is a mass of tissue, the limit of which is diffuse. Poor quality of the histological sections did not permit the description of additional details (Fig. 18C ).

Remarks.

This species presents all the characteristics of the subfamily Geoplaninae , i.e., creeping sole covering most of the ventral surface, mouth posterior to the midbody, a well-developed cutaneous musculature organized into bundles, part of the parenchymal muscle layers organized in longitudinal fibers, and dorsal testes (see Almeida et al. 2019).

Since the syntypes present only poorly developed copulatory organs, it is not possible to allocate the species to any other genus. Consequently, the species should remain in Pseudogeoplana .

Figures

Figure 16. Pseudogeoplana arpi (Schirch 1929) A fixed syntype A in dorsal view B original illustration of G. arpi by Schirch (1929) C virtual µCT reconstruction of body of Syntype A D dorsal view of syntype B.

Figure 17. Pseudogeoplana arpi (Schirch 1929), photomicrographs of syntype B A transverse section of anterior extremity B transverse section of pre-pharyngeal region C transverse section of anterior extremity D horizontal section of testicular region.

Figure 18. Pseudogeoplana arpi (Schirch 1929) A syntype A virtual sagittal section of pharynx, pixel size: 10 µm B syntype B diagrammatic reconstruction of sagittal sections of pharynx C syntype B photomicrograph of sagittal section of incipient copulatory apparatus D syntype B reconstruction of incipient copulatory apparatus.