Dolichoplana, Silva & Carbayo, 2020

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

Dolichoplana sp. Figures 20 , 21 , 22

Material examined.

Specimen 8922: unknown collecting site and date. Mislabeled as G. blaseri . Three dimensional (3D) images and virtual sections of specimen 8922 were obtained through microcomputed tomography. Subsequently, the following body parts of this specimen were histologically processed: Transverse sections of anterior extremity on 38 slides; horizontal sections of region immediately posterior to anterior extremity on 31 slides; transverse sections of pre-pharyngeal region on 31 slides; transverse sections of posterior extremity on 18 slides; remaining part of body preserved in 80 % ethanol.

External aspect.

Fixed worm ~90 mm long, and 2.5 mm wide. Body elongate, with parallel margins; dorsum convex, ventral side flat, and margins rounded. Anterior and posterior extremities blunt (Fig. 20A, C ). Dorsum ocher yellow in color, ornamented with five longitudinal stripes of terra brown color, i.e., median stripe bounded on either side by a paramedian stripe, externally to which is a lateral stripe. These stripes are irregularly faded, mainly in first quarter of body. Ventral side ochre yellow in mid-line, 0.9 mm in width, and terra brown laterally.

Single pair of eyes present at 4 mm from anterior extremity, 85 µm in diameter (Fig. 21A ). Sensory pits simple invaginations 25-30 µm deep, located marginally in single row. They are distributed between the second and fourth millimeters of the body. Mouth at a distance from the anterior extremity of the body equivalent to 29 % of body length.

Internal morphology.

Creeping sole comprising 35 % body width (Fig. 21B ). Abundant rhabditogen cells producing erythrophil granules pierce ventral and marginal epidermis.

Cutaneous musculature comprises three layers, namely a subepithelial circular layer (5 µm thick), followed by one diagonal layer with decussate fibers (10 µm thick), and then a well-developed innermost longitudinal layer (70 µm thick dorsally, 75 µm ventrally). Muscle fibers of the longitudinal layer are arranged into bundles of 21-54 fibers. Cutaneous musculature thickness relative to body height in the pre-pharyngeal region, 18 % (Fig. 21A, B ).

Five parenchymal muscle layers present: a dorsal layer (20 µm thick) of decussate diagonal fibers, a supraintestinal layer (40 µm thick) of transverse fibers, a subintestinal layer (30 µm thick) of transverse fibers, a subneural layer (40 µm thick) of longitudinal fibers, and a ventral layer (40 µm thick) of decussate diagonal fibers located inside the ventral cutaneous nerve net (Fig. 21C, D ).

Central nerve system formed by a pair of ganglia (Fig. 21A ) and a set of nerve fibers with the typical form of a rope ladder (Fig. 21B ).

Mouth situated at a distance from the root of the pharynx equivalent to 50 % of the pharyngeal pocket length. Pharynx cylindrical, not folded. Esophagus 0.5 mm in length. Pharynx at a distance from the anterior extremity of the body equivalent to 29 % of the body length (Fig. 22 ). Intestine typical of triclads, consisting of an anterior main branch and two posterior ones, all of them also branched (Fig. 20B ). Reproductive organs not developed.

Remarks.

It is evident that the external aspect of specimen 8922 does not agree with the original description and figure of the single type specimen of Ps. blaseri (Fig. 19 ). The original description reads: "Length: 160 mm. Width: 20 mm. Dorsum almost completely black, in just a few places it shows the ground color. Pharyngeal and gonopore openings are evident on the ventral side, at 95 mm and 110 mm from anterior extremity, respectively. Ventral side irregularly patterned with marble (so distinguishing from G. rufiventris )" (original in Portuguese). Schirch’s description and figure of Ps. blaseri match species of Obama ( Geoplaninae ), but every morphological aspect of specimen 8922 mismatches Schirch’s description. Furthermore, there is no individual resembling the original description of Ps. blaseri in Schirch’s collection. Thus, the type material, i.e., the holotype, of Ps. blaseri should be considered lost.

Specimen 8922 agrees with the diagnosis of Dolichoplana ( Rhynchodemidae ): body shape and size, position of mouth, number of eyes, and thickness of cutaneous longitudinal muscle ( Moseley 1877, Graff 1899, Hyman 1940). However, the diagnosis of Dolichoplana includes: "external longitudinal muscular bundles very much developed all over the body, but especially in the dorsal regions, where they are the only longitudinal muscles present" ( Moseley 1877); an attribute that specimen 8992 does not fit. However, the thin muscle layer, such as the circular and diagonal cutaneous muscles, are frequently only discernible in preparations sectioned in planes tangential to the layer. Moseley might have overlooked the dorsal circular and diagonal layers or, simply, his specimen did not possess them. Nonetheless, the diagnosis of Dolichoplana should be re-assessed.

Figures

Figure 19. Original illustration of G. blaseri by Schirch (1929).

Figure 20. Dolichoplana sp. Specimen MNRJ 8922 A specimen fixed in dorsal view B volume rendering reconstruction of body from µCT data C fixed specimen with original label.

Figure 21. Dolichoplana sp. Photomicrographs of specimen MNRJ 8922 A transverse section of cephalic region B transverse section of pre-pharyngeal region C horizontal section of pre-pharyngeal region showing dorsal muscles D horizontal section of pre-pharyngeal region showing ventral muscles.

Figure 22. Dolichoplana sp. Specimen MNRJ 8922. Virtual sagittal section of pharynx, pixel size: 11.92 µm.