Mapuplana guttulata, Grau & Almeida & Sluys & Carbayo, 2022

Grau, José Horacio, Almeida, Ana Laura, Sluys, Ronald & Carbayo, Fernando, 2022, A new genus and two new species of land planarians (Platyhelminthes: Tricladida: Geoplanidae) from Southern Chile, Journal of Natural History 56 (13 - 16), pp. 947-967 : 950-958

Mapuplana guttulata sp. nov.

Material examined

Holotype. MNHNCL PLAT-15045 (Field code, F4906). Monumento Natural Contulmo , Purén, Región de La Araucanía, Chile, (38.000°S, 73.183°W), coll. F. Carbayo, 12 December 2010. Transverse sections of the cephalic and ovarian region on 31 slides; horizontal sections of a portion behind the cephalic region on 25 slides; transverse sections of the pre-pharyngeal region on 17 slides; sagittal sections of the pharynx and copulatory apparatus on 62 slides.

Diagnosis

Species of Mapuplana measuring about 50 mm in length; yellowish dorsum with a dark, minutely reticulated pattern. Ventral cutaneous musculature is thickest in parasagittal planes. Male atrium twice as long as the female atrium. Entire length of the female genital duct receives openings of shell glands. Gonoduct vertical. Female atrium ovoid.

Type locality

Monumento Natural Contulmo, Southern Chile. This small natural reservation (82 ha) is one of the few protected fragments of native forest in the region. The area is dominated by the Nothofagus temperate rainforest, receiving up to 1500 mm of rain per year.

Etymology

The specific epithet is derived from the Latin guttula, meaning droplet, and alludes to the dots and marks adorning the dorsum.

Description

External appearance. The live specimen measured approximately 50 mm in length and 5 mm in width, while preserved it was 30.5 mm long, 6 mm wide, and 2.8 mm thick. The body is lanceolate, with the dorsum convex and the ventral side being only slightly convex. From about halfway along its length, the body tapers towards the front end, giving rise to a narrow head with a rounded anterior margin. Posteriorly, the body first widens and then tapers, thus acquiring the shape of a broad arrowhead ( Figure 2 (a)). In resting position, the dorsal surface is more or less corrugated, ie provided with wrinkles and folds. The ground colour of the dorsum is pastel yellow (RAL 1034), and it is adorned with scarce yellow-orange (RAL 2000) specks and numerous, small red-orange (RAL 2001) marks forming a minutely reticulated pattern ( Figure 2 (a,b)). A broad mid-dorsal stripe (11% of body width) grades from yellow-orange at mid-body to red-orange at the extremities of the body. This median stripe is composed of two thinner lines in some regions of the body. The ventral surface bears the same colour pattern as the dorsal surface, albeit the median band is lighter ( Figure 2 (c)).

The eyes are monolobated, ranging between 45 and 82 µm in diameter. The eyecups are distributed in a single-to-double marginal row, contouring the very anterior body margin and extending on either side of the body to the posterior margin. Sensory pits are absent. Instead, spots of cilia, housed in slight depressions, are located at the ventro-lateral portion of the cephalic region ( Figure 3 (a)). These sensory depressions are rare and inconspicuous, and were not observed in the anterior-most body region.

The width of the creeping sole was difficult to measure in the pre-pharyngeal region because of the abundant erythrophil secretion adhering to the ventral surface, but it occupies 57% of the body width in the cephalic region. Relative position of the mouth: body length is 61% in relation to the anterior tip of the body; that of the gonopore:body length is 78%.

Epidermis and its secretions. The epidermis is pierced by openings of three types of gland cells, producing erythrophil, cyanophil and xanthophil granules, respectively, with the erythrophil type being very abundant ventrally. In addition, rhabditogen cells pierce the dorsal and marginal portions of the epidermis. All types of glands are scarcer in the cephalic region. A glandular margin is absent ( Figure 3 (b)).

Cutaneous musculature. In the pre-pharyngeal region, the cutaneous musculature comprises three layers, namely a subepidermal circular layer (5–7.5 µm thick), followed by a double layer (12.5–20 µm) with decussate fibres, and a strong, innermost longitudinal muscle layer ( Figure 3 (c)). The longitudinal musculature is 80 µm thick dorsally and 400 µm ventrally; dorsally, the fibres are gathered in large bundles ( Figure 3 (c)). Ventrally the longitudinal musculature is divided into a subepidermal portion, which is about 65 µm thick and composed of small bundles, and a sunken dense portion, located beneath the cutaneous nerve plexus that measures 335 µm in thickness ( Figure 3 (d,f)). In the pre-pharyngeal region of the body the cutaneous musculature thickness relative to the body height (abbreviated CMI) corresponds to 12.5% in the mid-sagittal plane. This value increases to 20% in parasagittal planes, due to an increase in the thickness of this musculature ( Figure 3 (d,f)).

Parenchymal musculature. There are four parenchymal muscle layers, viz. a dorsal layer of decussate fibres (30 µm thick, 1.0% of the body height), a supraintestinal layer (70– 80 µm) of transverse fibres, a subintestinal transverse muscle layer (65–83 µm), and a fourth, subneural layer with diagonal decussate fibres (90–120 µm); the subneural layer is embedded in the insunk ventral cutaneous muscle layer ( Figure 3 (d)).

Musculature in cephalic region. In the cephalic region, the musculature is relatively stronger than in the pre-pharyngeal region and it is also organised differently ( Figure 4 ). At 1 mm from the anterior tip of the body, the ventral sunken longitudinal musculature is concentrated along the longitudinal body axis, so that it occupies about 67% of the body width, while the subepidermal portion represents 63% ( Figure 4 (a)); in this region CMI is 35%. At 460 µm from the anterior tip of the body, the width of the subepidermal and sunken longitudinal muscle layers relative to body width and CMI decreases to 58% and 34%, respectively ( Figure 4 (c,d)); in this region of the body the transverse muscle fibres are relatively more abundant than in the pre-pharyngeal region, while the subneural muscle fibres are restricted to mid-body. In this region, the sunken fibres are apparently oriented obliquely towards the dorsal body surface and to the body margins, but the precise path followed by these fibres was not discernible beyond the central nervous system ( Figure 4 (c)). At 100 µm from the anterior tip, the sunken portion of the ventral longitudinal cutaneous musculature is lacking, while the subepidermal portion is still present.

Pharynx. The cylindrical pharynx is located at a short distance behind the middle of the body and projects out of the mouth opening, the latter situated at the posterior end of the pharyngeal pouch ( Figure 5 (a)). The oesophagus is 0.5 mm long. The pharyngeal pouch musculature is composed of subepithelial longitudinal muscle fibres, followed by circular fibres. The outer pharyngeal musculature consists of a subepithelial longitudinal muscle layer (8 µm thick), followed by a layer of circular muscles (20–25 µm thick). Underneath this coat of muscles, there is a 200 µm thick layer of intermingled longitudinal and circular muscle fibres. The inner pharyngeal musculature consists of a single, subepithelial layer of intermingled circular and longitudinal fibres (120–225 µm thick) ( Figure 5 (b)). Radial muscle fibres are also present. Two types of glands, producing granular erythrophil and xanthophil secretions, respectively, run through the parenchyma of the pharynx and discharge their contents at the tip of the pharynx.

Male reproductive system. The globular testes, measuring 210–320 µm in diameter, are distributed in two rows on either side of the body between the supra-intestinal transversal parenchymatic muscle layer and the intestinal diverticula ( Figure 3 (b,c)). The anterior-most testes are located at a distance from the anterior tip of the body equivalent to 22% of the body length; the posterior-most testes are located at the equivalent of 50% of body length, as measured from the anterior margin, ie they are distributed anteriorly to the root of the pharynx.

The sperm ducts run immediately above the sub-intestinal parenchymal musculature and slightly laterally to the oviducts. Posterior to the pharynx, these ducts are sinuous and dilated, thus forming spermiducal vesicles, which are packed with spermatozoa.

The posterior portions of the spermiducal vesicles narrow considerably while curving postero-dorsad and, subsequently, communicate with a branch of one of the highly ramified glands of the tubular prostatic vesicle. This communication of the sperm ducts with the ducts of the prostatic glands takes place via a transitional canal lined with a low epithelium, which is surrounded by a 10 µm thick layer of circular muscle. These two glands consist of numerous ramified ducts, which measure 15–37 µm in diameter and are lined with a 37–40 µm high, ciliated epithelium. These ducts collect erythrophil and xanthophil granular secretions, produced by gland cells located all around the tubules ( Figures 5 (c) and 6(c,d)). The tubular glands join before opening into the very proximal, posterior portion of the prostatic vesicle ( Figure 5 (c)).

The unpaired tubular prostatic vesicle follows a spiralling trajectory ( Figures 5 (c) and 6 (b,c)) before it penetrates the ventral musculature of the common muscle coat and, subsequently, ascends to open into the ejaculatory duct. The proximal, anterior portion of the prostatic vesicle measures 35–50 µm in diameter, while its distal section measures 10–18 µm ( Figures 5 (c) and 6(b,c)). The prostatic vesicle is lined with a cuboidal, ciliated epithelium and is surrounded by a 50–75 µm thick layer of circular muscle.

On its way through the penis papilla, this duct doubles its diameter to 60 µm before narrowing again to open at the tip of the papilla through an opening with a diameter of about 5 µm. The ejaculatory duct is lined with a ciliated epithelium and is surrounded by a 30 µm thick layer of circular musculature.

The small penis papilla is conical, with its length corresponding to about 9% of the length of the male atrium ( Figures 5 (c) and 6(e)). This papilla projects from the anterodorsal portion of the male atrium and points postero-ventrally; it is covered with an infranucleated epithelium, which is pierced by two types of gland cells, producing xanthophil and cyanophil granules, respectively. The epithelium of the penis papilla is underlain by a 17–20 µm thick, subepithelial layer of circular muscle, followed by a 15– 33 µm thick layer of longitudinal fibres.

The male atrium is long, provided with distinct folds and lined with a low epithelium. ( Figures 5 (c) and 6(a,b)).Two large,transverse flap-shaped folds occupy the anterior half of the male atrium. One flap is ventral to the penis papilla, the other posterior to it. The posterior half of the male atrium is occupied by two oblique folds, the anterior one being narrower than the posterior one. The basement membrane underlying the epithelium that is located between the flaps, as well as that between the oblique folds, is 4–8 times thicker than in any other region of the atrium. The entire epithelium of the male atrium is pierced by openings of gland cells producing erythrophil granules, while it is underlain by a 18–35 µm thick layer of circular muscle fibres. Transverse and longitudinal muscle fibres are abundant in the flaps and oblique folds. Additionally, the posterior oblique and narrow fold is reinforced with a 75–85 µm thick coat of intermingled circular and longitudinal muscle fibres. A strongly xanthophil clump, 250 × 350 µm in size, is attached to the wall of the atrium between the two oblique folds; the atrial surface where the clump is attached lacks epithelium ( Figures 6 (b) and 7(a)).

Female reproductive system. A single pair of ovaries is located at a distance from the anterior tip of the body corresponding to 23% of the body length, with the gonads being situated on top of the ventral nerve plate and underneath the transverse sub-intestinal parenchymal muscle layer. The ovaries are approximately globular, measuring about 250 µm in diameter. The ovovitelline ducts emerge from the dorsal wall of the ovaries and, thereafter, run above the nerve plate. Posteriorly to the gonopore, the ducts ascend to open into the female genital duct, which is about 120 µm wide and curves antero-dorsally to communicate with the female atrium (ie proflex with anterior approach; Figure 5 (c)). Approximately two-thirds of the length of the female genital duct receives the openings of shell glands; at the point of communication with the female atrium, this duct diminishes somewhat in diameter ( Figures 5 (c) and 7(b,c)). The female genital duct is lined with a columnar epithelium, with the apical portion of its cells containing xanthophil granules.

The gonoduct originates from the mid-ventral wall of the female atrium, the latter being spacious and more or less ovoid in shape, with its length being about half of that of the male atrium ( Figures 5 (c) and 7(b,c)). The female atrium is lined with a 40–100 µm high, somewhat irregular, nucleated epithelium, which exhibits some recesses that are sunken into the underlying parenchyma ( Figure 7 (d)). The cytoplasmic membrane of the epithelial cells could not be recognised. Most of the cytoplasm of these cells has low affinity for stain, while the apical portion of the cells is provided with a bright, xanthophil secretion. The female atrium is surrounded by a 25 µm thick, subepithelial, layer of circular musculature, followed by a loose coat of longitudinal fibres.

A blind duct, measuring about 140 µm in width and 520 µm in length, opens into the antero-lateral region of the female atrium ( Figures 5 (c) and 7(e,f)). This duct is lined with a cuboidal epithelium, which is pierced by the openings of two types of gland cells, producing erythrophil and cyanophil granules, respectively. The blind duct is surrounded by a 20 µm thick layer of circular muscle.

The female atrium houses a spermatophore, with a shape between ovate and quadrate ( Figures 6 (a) and 7(c)), about 550 × 300 µm in size. It is composed of a strongly xanthophil substance – similar to that of the clump in the male atrium – and is amorphous in its central portion, whereas it is fibrous at its periphery. Small portions at the innermost region of the spermatophore contain sperm.

The common muscular coat consists of longitudinal and oblique muscle fibres, and surrounds the distal region of the prostatic vesicle, the male and female atria, and the female genital duct.

Figures

Figure 2. Mapuplana guttulata. Photographs of the live holotype in dorsal (a, b) and ventral (c) views. Scale bars not available.

Figure 3. Mapuplana guttulata. Photomicrographs of histological sections. (a) Transverse section of the cephalic region, showing the sensory depression (arrowhead); (b–d) transverse sections of the prepharyngeal region; (e, f) horizontal sections showing cutaneous and parenchymal muscles (anterior at the top).

Figure 4. Mapuplana guttulata. Photomicrographs of transverse sections of the anterior region of the body, located at (a) 1000 µm, (b)900 µm, (c, d) 500 µm, and (e, f) 400 µm from the anterior extremity of the body.

Figure 5. Mapuplana guttulata. (a) Photomicrograph of a sagittal section of the pharynx and male copulatory organ; (b) photomicrograph of outer and inner pharyngeal musculature of the paratype; (c) diagrammatic reconstruction of the copulatory apparatus.

Figure 6. Mapuplana guttulata. Photomicrographs, sagittal sections. (a) Copulatory apparatus; (b) male atrium; (c) prostatic vesicle; (d) tubulous gland of the prostatic vesicle; (e) penis papilla.

Figure 7. Mapuplana guttulata. Photomicrographs, sagittal sections. (a) Male atrium and the xanthophil clump; (b–c) female atrium; (d) epithelium of female atrium (arrowheads indicate epithelial recesses sunken into the underlying parenchyma); (e, f) blind duct opening into the female atrium.