Pseudogeoplana wetzeli (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 wetzeli (Schirch, 1929) Figures 27 , 28 , 29

Geoplana wetzeli Schirch, 1929: 32. Type locality: Baixo Guandu, Espírito Santo, Brazil.

Pseudogeoplana wetzeli : Ogren and Kawakatsu 1990: 160.

Material examined

(Fig. 27A, B ). Type material. Seven syntypes. Baixo Guandu, Espírito Santo, Brazil. P. Schirch leg., 1917. They were received on loan in 70 % ethanol with only a label reading 218. Each syntype was given an additional identification with a letter, A-G. Parts of the body of syntype MNRJ 218A were first studied using µCT followed by traditional histology: transverse sections of anterior extremity on 26 slides; horizontal sections of ovarian region on 29 slides; sagittal sections of pharyngeal region on 33 slides and transverse sections of post-pharyngeal region on 18 slides. Remaining part of body preserved in 80 % ethanol. Following seven syntypes were examined and retained in 80 % ethanol: syntypes MNRJ 218B, C, D, E, F, G. Parts of them were fragmented.

External aspect.

Fixed syntype A (Fig. 27A ) measured 30 mm long, 3 mm wide, and ~1.2 mm high; other syntypes are smaller (Fig. 27B ). Anterior extremity rounded, posterior pointed, body sides rounded. Dorsum convex, ventral side flat. Ground color of the dorsum olive brown with a median band (as wide as 1/3rd of body width) of mahogany brown color that does not reach the extremities of the body (Fig. 27B ). Schirch (1929) illustrated the external aspect of the species (Fig. 27C ). Ventral side lemon yellow (Fig. 27D, E ).

Eyes monolobate, 38 µm in diameter and surround the anterior extremity of the body (Fig. 27F ). Posterior to the second millimeter, the eyes spread onto the dorsum and at 4.5 mm occupy the entire dorsum. Sensory pits are simple invaginations 40 µm deep, located ventro-marginally in a single row at least along a body length of ~5 mm (equal to 17 % of the body length, syntype A; Fig. 28A ). Relative position of the mouth: body length, ~52 % (syntype A). Gonopore not developed in any syntype.

Internal aspect.

The creeping sole comprises 72 % of the body width. Rhabditogen cells and glands producing erythrophil granules pierce the dorsal and marginal epidermis and creeping sole. Ventral epithelium is pierced by a few glands producing fine xanthophil granules. Glandular margin is absent.

Cutaneous musculature comprises three layers typical of the subfamily Geoplaninae . A subepithelial circular layer, followed by a diagonal layer with decussate fibers (2 µm thick dorsally; 2.5 µm thick ventrally) and an innermost longitudinal layer. Muscle fibers of the longitudinal layer (20 µm thick dorsally; 25 µm thick ventrally) are arranged into bundles of 6-19 fibers each. Cutaneous musculature thickness relative to the body height in the post-pharyngeal region, 4.5 %.

Parenchymal musculature formed by a supraintestinal layer of transverse fibers and a subintestinal layer of transverse fibers, both layers interspersed with longitudinal fibers (Fig. 28B, C ). Longitudinal parenchymal muscle fibers were best observed in the ovarian region; in the pharyngeal region longitudinal fibers are scarcer. Suboptimal quality of the horizontal sections did not permit us to check whether a third layer, typical of the Geoplaninae (dorsal layer of decussate fibers) is present. In the cephalic region, cutaneous and parenchymal muscle layers are arranged as in the remainder of the body but are less developed. Ventral nerve plate present (Fig. 28B, D ).

Mouth situated approximately in the middle of the pharyngeal pouch. Pharynx cylindrical (Fig. 29A, B ). Outer pharyngeal musculature consisting of a thin subepithelial longitudinal muscle (5 µm thick), followed by a 25 µm thick circular muscle with longitudinal fibers interspersed (Fig. 29C, D ). Lining epithelium of pharyngeal lumen sinuous and ciliated, and underlain by a subepithelial circular muscle (25 µm thick), followed by a longitudinal layer (5 µm). Esophagus absent.

Testes ~40 µm in diameter. They are located dorsally between the supraintestinal parenchymal muscle layer and the intestine, and limited dorsolaterally (Fig. 28C ). Anteriormost testes distant from the anterior extremity 5 mm, equivalent to 17 % of the body length; posteriormost testes distant from anterior extremity, i.e. 10.4 mm, equivalent to ~35 % of the body length (syntype A). Incipient sperm ducts only. Copulatory apparatus not developed.

Ovaries are oval, 170 µm in maximum length, and situated immediately above the ventral nerve plate (Fig. 28B ). They are located at ~6 mm from the anterior extremity, equivalent to 20 % of the body length (syntype A). Ovovitelline ducts emerge from the dorso-lateral region of ovaries and extend posteriorly only ~200 µm. They contain sperm.

Remarks.

Diagnostic features of the Geoplaninae are recognized in this species: creeping sole covering most of ventral surface, mouth posterior to mid-body, well-developed cutaneous musculature organized into bundles, part of the parenchymal muscle layers organized in longitudinal fibers (as they may be present in the subfamily) and testes dorsal (see Carbayo et al. 2013, Almeida et al. 2019).

Although the largest specimen exhibits both male and female gonads, even sperm in ovovitelline ducts, the copulatory apparatus is lacking, the absence of which hinders searching for the taxonomic affinities of this species within the Geoplaninae .

An uncommon feature within this subfamily, the parenchymal longitudinal muscle fibers, might shed some light on the genus to which this species belong. These parenchymal fibers are only known from species of Geoplana and Imbira . However, Geoplana is excluded, since in species of this genus, eyes in the cephalic region are cone-shaped, whereas in Ps. wetzeli they are rounded. Regarding the longitudinal parenchymal musculature, the diagnosis of Imbira does not exclude Ps. wetzeli , but in Imbira , the eyes are distributed only marginally (vs. dorsal in Ps. wetzeli ). In view of the lack of knowledge on the morphology of this species, it should remain in the collective genus Pseudogeoplana .

Figures

Figure 27. Pseudogeoplana wetzeli (Schirch 1929) A dorsal view of syntype A in 80 % ethanol after being sectioned for histological processing B set of all syntypes with original labels C original illustration of G. wetzeli by Schirch (1929) D ventral view of s yntype A in 80 % ethanol on graph paper E ventral view of cephalic region of syntype A F lateral view of cephalic region of syntype A in clove oil.

Figure 28. Pseudogeoplana wetzeli (Schirch 1929). Photomicrographs of syntype A. A Horizontal section of anterior extremity B horizontal section of ovarian region C horizontal section of testicular region D transverse section of anterior extremity.

Figure 29. Pseudogeoplana wetzeli (Schirch 1929), syntype A. A Virtual section of pharynx, pixel size: 4.77 µm B photomicrograph of sagittal section of pharynx C photomicrograph of tangential section of outer epithelium of pharynx and its muscle, in sagittal plane D photomicrograph of sagittal section of outer epithelium of pharynx and its underlying muscle.