Myoplana joaopauloi

Almeida, Ana Laura, Álvarez-Presas, Marta & Carbayo, Fernando, 2023, The discovery of new Chilean taxa revolutionizes the systematics of Geoplaninae Neotropical land planarians (Platyhelminthes: Tricladida), Zoological Journal of the Linnean Society 197 (4), pp. 837-898 : 868-872

MYOPLANA JOAOPAULOI ALMEIDA & CARBAYO SP. NOV.

( FIGS 24–27 )

Zoobank registration: urn: lsid: zoobank. org:act: A4D8AE61-85C5-49A4-A57E-E2B5AD577454

Holotype: MNHNCL PLAT-15050 (Field code, F4875). Parque Nacional Nahuelbuta, Región de Purén, Chile (37°49′′39.2′′S, 073°00′′35.0′′W), coll. F. Carbayo et al.,

9 December 2010. Cephalic region: transverse sections on 13 slides; ovarian region: horizontal sections on 27 slides; pre-pharyngeal region: transverse sections on 28 slides; pharynx and copulatory apparatus: sagittal sections on 32 slides.

Type locality: Parque Nacional Nahuelbuta, Purén, Malleco Province, Región La Araucanía, Chile. The species is only known from this locality.

Etymology: The specific name pays homage to João Paulo Gonzaga de Paula, a teacher in the public school E. M. E. F. Henrique Souza Filho Henfil, and most influential in the humanistic formation of children.

Diagnosis: Species of Myoplana with an inconspicuous dorsal light mid stripe. Short, distal portion of the sperm ducts runs anteriorly. Penis papilla projects from the ventro-anterior region of the male atrium.

Description

External aspect: The specimen was not measured alive. Preserved, it was 32 mm in length, 5.5 mm in width, and 1.7 in height. The body margins are parallel; the anterior tip is pointed and the posterior tip is rounded. The dorsum is slightly convex; the ventral surface is flat ( Fig. 24 ). The dorsal colour of the live specimen is black-brown (RAL 8022), passing into beige-brown (RAL 8024) in the anterior extremity. A thin inconspicuous light stripe runs medially ( Fig. 24C ). The colour of the body margins is cream (RAL 9001). The ventral surface is light-grey (RAL 7035), mottled with brownish dots in the extremities of the body ( Fig. 28B, C ).

The eyes are of a single-cup type measuring 40 µm in diameter. They are placed in haloes and are distributed in a row contouring the anterior 5 mm of the body. Backward they form one to two marginal rows until the posterior tip. The sensory pits are approximately 45 µm deep. They contour the anterior region of the body and extend backward ventromarginally along a portion the body equivalent to 28% of its length. The mouth is positioned at a distance from the anterior extremity equal to 75% of the body length; the gonopore, 87.5%.

Internal morphology: The creeping sole occupies the entire ventral surface. The entire epidermis is pierced by the necks of abundant rhabditogen cells and by three types of cells producing erythrophil amorphous secretion, xanthophil amorphous secretion and erythrophil granules, respectively. Ventrally, erythrophil granules are much more abundant, while the xanthophil secretion is less abundant than dorsally. The narrow glandular margin consists of two types of gland cells producing erythrophil and xanthophil granules, respectively. The main nervous system is organized in a 220 µm thick plate, representing approximately 13.5% of the body height ( Fig. 25A ).

The cutaneous musculature comprises three layers, namely, a subepidermal layer of circular fibres (5 µm thick), followed by a double layer (20 µm) with diagonal fibres and then a well-developed, innermost layer of longitudinal fibres (55–145 µm thick, dorsally and ventrally, respectively). The latter layer is divided into a subepithelial portion and a portion sunken into the parenchyma representing 78% of the total thickness of the ventral layer ( Fig. 25 ). The cutaneous musculature thickness relative to the body height in pre-pharyngeal region is 15%.

Four parenchymal muscle layers are present, namely, a dorsal layer of decussate fibres, a supraintestinal layer of transverse muscle, a subintestinal layer of transverse muscle and a transneural layer of diagonal fibres. The muscle fibres of the transneural layers are located among the components of the main nerve plate and extend until the inner cutaneous nerve plexus. Oblique muscle fibres run from the dorsal to the lateroventral epidermis.

The mouth is situated at a distance from the root of the pharynx, equivalent to one-third of pharyngeal pouch length ( Fig. 26A ). The pharyngeal pouch is close to the prostatic vesicle. An oesophagus is present. The oesophagus to pharynx length ratio is 42%. The pharynx is bell-shaped ( Fig. 26A ). Three types of gland cells discharge their xanthophil, erythrophil and cyanophil granules, respectively, through the covering epithelium of the distal portion of the pharynx. The outer pharyngeal musculature consists of a subepithelial layer of longitudinal muscle (20 µm thick), followed by a layer of circular muscle (67.5 µm thick) and a layer of longitudinal muscle (40 µm thick). The inner pharyngeal musculature consists of a subepithelial layer (10– 12 µm thick) of longitudinal fibres, followed by a layer (40 µm) of diagonal fibres, a circular muscle (200 µm) and an innermost longitudinal muscle (72 µm). Numerous radial muscle fibres run between the outer and inner pharyngeal epithelia.

The testes are approximately 330 µm in diameter and are distributed into two to three rows at each side of the body. They are dorsally located between the supra-intestinal parenchymal musculature and the intestine ( Fig. 25A ). The anteriormost testes are located at a distance from the anterior tip of the body equivalent to 15.5% of the body length; the posteriormost testes, the equivalent to 70%, i.e. they are lateral to the pharyngeal root.

The sperm ducts run posteriorly until a position lateral to the male atrium. Subsequently, they bend anteriorly before opening laterally into the proximal region of the prostatic vesicle ( Fig. 26C ). These ducts are lined with a squamous epithelium and are filled with sperm, except in their distal section. The prostatic vesicle is extrabulbar and is attached to the anterior side of the penis bulb. The pear-shaped, anterior-half of this vesicle runs dorsoposteriorly, subsequently penetrates the anterior region of the penis bulb and continues with the sinuous ductalhalf, which communicates with the ejaculatory duct. This vesicle is lined with an epithelium varying from squamous to columnar. Cilia covering the epithelium are only present in the ductal portion. The epithelium of the prostatic vesicle is pierced by the necks of three types of gland cells producing erythrophil, xanthophil and cyanophil granules, respectively. This epithelium of the extrabulbar portion is surrounded by a single layer (25 µm thick) of decussate fibres, while that of the intrabulbar portion is surrounded by a layer (7.5 µm) of circular fibres.

The ejaculatory duct opens at the tip of the penis papilla. This duct is lined with a cuboidal, ciliated epithelium, which is traversed by the necks of gland cells producing cyanophil granules. A circular muscle (2 µm thick) surrounds this duct. The small penis papilla is conical and lies horizontally. This papilla occupies approximately the anterior-tenth of the male atrium and is placed in the ventral region of the penis bulb ( Figs 26C , 27B ). The penis papilla is lined with a columnar epithelium, which is pierced the necks of gland cells producing fine erythrophil granules. This epithelium is underlain by a muscle of scattered circular fibres (4 µm thick).

Narrow anteriorly, the male atrium widens progressively to subsequently be narrowed by a distal, traverse fold, the dorsal section of which is continued with a lateral fold of the female atrium ( Figs 26C , 27D ). The male atrium is lined with a columnar epithelium, which is rugged in some sections. This epithelium is pierced by the necks of gland cells producing fine erythrophil granules; additionally, the necks of glands producing cyanophil granules pierce the dorsoanterior-half of the atrium. The atrial epithelium is underlain by a layer of circular muscle (5 µm thick), followed by a layer of longitudinal muscle (10 µm thick), which is only present in the anteriormost and posteriormost sections of the atrium.

The ovoid ovaries have a maximum diameter of 280 µm and are located at a distance from the anterior tip of the body, equivalent to 8.5% of the body length. The ovovitelline ducts emerge from the dorsal portion of the ovaries and run ventrally above the nerve plate. Anteriorly to the gonopore, these ducts run dorsoposteriorly to join the common glandular ovovitelline duct. This common duct is located dorsad to the female atrium and runs posteroventrally to communicate with the conspicuous female genital canal. This canal is C-shaped in lateral view and projects from the posterior region of the female atrium.

The female atrium is funnel-shaped and presents a lateral fold that continues from the male atrium ( Figs 26C , 27E ). The female genital canal and female atrium are lined with a columnar (60 µm high) epithelium, the cells of which are stained reddish apically. This epithelium is pierced by the necks of gland cells producing erythrophil granules and is underlain by a circular muscle (25 µm thick) with longitudinal fibres interspersed. Toward the gonopore canal, these two types of muscle fibres are separated into two layers, each 7 µm thick. Additionally, an ectal reinforcement of longitudinal fibres is located posterior to the female genital canal ( Fig. 27E ).

Figures

Figure 24. Myoplana joaopauloi sp. nov. Photographs of the live holotype. A, dorsal view. B, dorsal view, with the posterior region upside down. C, convolute live holotype, showing haloes in the anterior margin. Scale bars not available.The specimen is approximately 30 mm long.

Figure 25. Myoplana joaopauloi sp. nov. Photomicrographs. A, transverse section of the pre-pharyngeal region. B, horizontal section of the dorsal region of the body showing the muscle layers. C, horizontal section of the ventral region of the body showing the muscle layers. D, transverse section of the ventral region of the body. E, sagittal section behind the pharyngeal pouch.

Figure 26. Myoplana joaopauloi sp. nov. A, photomicrograph of a sagittal section of the pharynx. The region within the rectangle in (B). B, photomicrograph of a sagittal section of the ventroanterior region of the pharynx. C, diagrammatic reconstruction of the copulatory apparatus.

Figure 27. Myoplana joaopauloi sp. nov. Photomicrographs of sagittal sections. A, anterior region of the prostatic vesicle. B, prostatic vesicle and penis papilla. C, penis papilla tangentially sectioned. D, general view of the copulatory apparatus. E, female atrium.

Figure 28. Myoplana Ʋeraluciae sp. nov. Photographs. A, live holotype in dorsal view. B, ventral view of the posterior-half of the live holotype. C, preserved holotype. Scale bars not available.