Cratera nigrimarginata, Rossi, Ilana & Leal-Zanchet, Ana, 2017

Rossi, Ilana & Leal-Zanchet, Ana, 2017, Three new species of Cratera Carbayo et al., 2013 from Araucaria forests with a key to species of the genus (Platyhelminthes, Continenticola), ZooKeys 643, pp. 1-32 : 8-14

Cratera nigrimarginata sp. n.

Material examined.

Holotype: MZUSP PL.1691: leg. I. Rossi, 18 July 2015, General Carneiro ( Araucaria Natural Heritage Private Reserve), state of Paraná, Brazil - anterior region in three fragments on 114 slides; pre-pharyngeal region: transverse sections on 10 slides; pharynx: sagittal sections on 19 slides; copulatory apparatus: sagittal sections on 17 slides.

Other specimens: all specimens sampled in the same locality as the holotype. MZU PL.00220: leg. I. Rossi, 6 February 2015 - anterior tip: transverse sections on 24 slides; anterior region at the level of the ovaries: sagittal sections on 78 slides; pre-pharyngeal region: transverse sections on 16 slides; pharynx: sagittal sections on 40 slides; copulatory apparatus: sagittal sections on 33 slides. MZU PL.00221: leg. J. L. A. Braccini, 4 June 2015 - copulatory apparatus: horizontal sections on 20 slides.

Diagnosis.

Species of Cratera with light-brownish dorsal colour bordered by dark margins; eyes dorsal with clear halos and bilobed appearance; pharynx cylindrical; prostatic vesicle with unbranched and dilated proximal portion; tip of penis papilla with infolds projecting into ejaculatory duct; cyanophil glands pierce male atrium evenly distributed.

Description.

External features.Body elongate, flat and with parallel margins; anterior tip rounded and posterior tip pointed (Figs 20-22). When creeping, maximum length 57mm. After fixation, maximum length 47mm. Mouth and gonopore located at posterior fourth of body (Table 3).

Live animals with dorsal surface light-brownish, constituting broad band, bordered by greyish or black margins; cephalic region greyish (Figs 20-22). Ventral surface pale yellow (Fig. 21). Under stereomicroscope, dorsal band bordered by thin black paramarginal stripes. After fixation, besides dorsal band and paramarginal stripes, dorsal surface may contain inconspicuous median stripe (Fig. 23); ventral surface becomes whitish with greyish margins and anterior tip. In preserved specimens, dorsal band with maximum width of about two thirds of body width. Paramarginal stripes, with nearly 1/12th of body width, begin behind the cephalic region (approximately anterior 1/9th of body) and converge towards posterior tip (Figs 23, 25).

Eyes, initially uniserial and monolobate, surround anterior tip (Figs 24-25). After second millimetre of body, eyes become larger and with bilobated appearance (Fig. 27), spreading onto dorsal surface and occupying almost all body width in anterior third of body (Fig. 24). Some eyes surrounded by inconspicuous small clear halos over paramarginal stripes (Figs 25-26). Eyes less numerous towards posterior tip. Diameter of pigment cups 15-40 µm.

Sensory organs, epidermis and body musculature.Sensory pits (Fig. 28), as simple invaginations (30-40 µm deep), contour anterior tip and occur ventromarginally in irregular, single row in anterior 1/8th of body. Creeping sole occupies 90% of body width in pre-pharyngeal region.

Three types of glands discharge through whole epidermis of pre-pharyngeal region: rhabditogen cells with xanthophil secretion (ventrally with smaller rhabdites), cyanophil glands with amorphous secretion and xanthophil glands with fine granular secretion (Figs 31-32). Few erythrophil glands with fine granular secretion open through ventral epidermis. Glandular margin conspicuous (Figs 29-30), after first millimetre of body. At least five types of glands constitute glandular margin: xanthophil glands with coarse granules of two types (heavily and slightly stained), cyanophil glands of two types (coarse granular and amorphous secretion) and erythrophil glands with coarse granules. Glands discharging through anterior tip of body similar to those of pre-pharyngeal region (Fig. 28).

Cutaneous musculature with usual three layers (circular, oblique and longitudinal layers); longitudinal layer with thick bundles (Figs 29-32, Table 4). Thickness of cu taneous musculature between two and four times that of epidermis (Table 4). Ventral musculature with similar thickness or slightly thicker than dorsal musculature at sagittal plane in pre-pharyngeal region (Table 4). Musculature becoming progressively lower towards body margins. In relation to body height, cutaneous musculature thinner in pre-pharyngeal region than in cephalic region, especially ventral musculature (Table 4, Fig. 28); thickness gradually diminishes towards anterior tip.

Mesenchymal musculature (Figs 28-29, 31-32) well developed, mainly composed of three layers: (1) dorsal subcutaneous, located close to cutaneous musculature, with decussate fibres (6-10 fibres thick), (2) supra-intestinal transverse (8-14 fibres thick) and (3) sub-intestinal transverse (10-18 fibres thick). Mesenchymal musculature more developed in cephalic region (Fig. 28) than in pre-pharyngeal region, especially dorsal subcutaneous musculature (12-20 fibres thick).

Digestive system.Pharynx cylindrical, approximately 6% of body length, occupies 70% of pharyngeal pouch. Pharyngeal dorsal insertion slightly shifted posteriorly (Fig. 33); mouth in median third of pharyngeal pouch. Oesophagus short with folded wall. Oesophagus: pharynx ratio 4%-12%.

Pharynx and pharyngeal lumen lined by ciliated, cuboidal epithelium with insunk nuclei. Pharyngeal glands constituted by four secretory cell types: abundant erythrophil glands with fine granular secretion, xanthophil glands with coarse granular secretion, as well as two types of cyanophil glands (with amorphous and fine granular secretions). Outer pharyngeal musculature (10-30 µm thick) comprised of thin subepithelial layer of circular fibres, followed by thin layer of longitudinal fibres. Inner pharyngeal musculature (70-90 µm thick) comprises thick subepithelial layer of circular fibres, followed by thinner layer of longitudinal fibres. Outer and inner muscle layers gradually become thinner towards pharyngeal tip. Oesophagus lined by ciliated, cuboidal to columnar epithelium with insunk nuclei. Musculature of oesophagus (70-120 µm thick) composed of thick layer with circular fibres, followed by layer of longitudinal fibres.

Reproductive organs.Testes in one irregular row on either side of body, located beneath dorsal transverse mesenchymal muscles (Figs 29, 31), begin slightly posteriorly to ovaries, in anterior third of body, and extend to near root of pharynx (Table 3). Sperm ducts medial to ovovitelline ducts, among fibres of sub-intestinal transverse mesenchymal musculature, forming spermiducal vesicles laterally to pharynx. Distally, spermiducal vesicles penetrate into lateral wall of proximal portion of prostatic vesicle (Figs 35-36, 38). Prostatic vesicle extrabulbar, unpaired, consisting of two portions: proximal portion short and dilated and distal portion tubular and sinuous. Proximal portion displaced ventrally in relation to distal portion and located closer to ventral epidermis than to dorsal epidermis (Figs 35, 37). Prostatic vesicle of specimen MZU PL.00220 showing larger lumen, filled with secretions. Ejaculatory duct almost straight, expanding at tip of penis papilla. Male atrium without folds. Penis papilla conical and symmetrical (Figs 35-38, Table 3). Tip of penis papilla occupying distal part of female atrium; with infolds projecting into ejaculatory duct (Fig. 40).

Lining epithelium of sperm ducts cuboidal and ciliated; thin muscularis (about 5 µm thick) constituted of interwoven circular and longitudinal fibres. Prostatic vesicle lined with ciliated, columnar epithelium. Muscularis of prostatic vesicle (20-40 µm thick) comprises mainly circular fibres mixed with longitudinal and oblique fibres (Fig. 39). Ejaculatory duct lined with ciliated, tall columnar epithelium (Fig. 40). Muscle coat of ejaculatory duct (5-10 µm) constituted of interwoven circular and longitudinal fibres. Erythrophil glands with fine granular secretion as well as cyanophil glands with amorphous secretion open into both prostatic vesicle and ejaculatory duct (Fig. 39). Penis papilla and male atrium lined with non-ciliated, columnar epithelium. Numerous cyanophil glands with amorphous secretion and few erythrophil glands with fine granular secretion open evenly distributed through penis papilla and male atrium. Muscularis of penis papilla (10-20 µm thick) and male atrium (6-10 μm thick) comprised of subepithelial layer of circular fibres, followed by layer of longitudinal fibres.

Vitelline follicles (Figs 29, 31, 34) situated between intestinal branches. Ovaries ovoid (approximately 200 µm in diameter) located dorsal to ventral nerve plate, in anterior fourth of body (Fig. 34, Table 3). Ovovitelline ducts emerge laterally from posterior half of ovaries and run posteriorly immediately above nerve plate. Ascending portion of ovovitelline ducts located lateral to female atrium. Common glandular ovovitelline duct short, located dorsally to posterior third of female atrium. Female genital duct dorso-anteriorly curved (Figs 35-37, 41). Female atrium oval-elongate with folded walls (Figs 35, 37), longer than male atrium (Table 3).

Ovovitelline ducts and common ovovitelline duct lined with ciliated, cuboidal to columnar epithelium and covered with intermingled circular and longitudinal muscle fibres (3-10 μm). Abundant shell glands with erythrophil secretion, besides cyanophil glands, empty into common glandular ovovitelline duct as well as into distal third of ascending portion of ovovitelline ducts (Figs 35-38, 41). Epithelial lining of female genital duct and atrium tall columnar, showing irregular height and sometimes stratified appearance (50-300 µm thick), ciliated in female duct. Epithelial cells with some lacunae containing cyanophil secretion (Figs 37, 41). Abundant cyanophil glands with amorphous secretion and less numerous erythrophil glands with fine granules open into female duct and atrium. Muscularis (10-20 µm thick) of female genital duct and atrium composed of interwoven circular and longitudinal fibres. Specimen MZU PL.00220 shows poorly developed vitelline follicles, but copulatory organs, including shell glands, fully developed.

Male and female atria broadly communicated each other, without separating folds (Figs 35-38). Common muscle coat thin along both male and female atria, thicker dorsally than ventrally, composed of circular, longitudinal and oblique fibres. Gonoduct vertical, lined with ciliated columnar epithelium. Numerous cyanophil glands with amorphous secretion and rhabditogen glands open into gonoduct. Muscularis of gonoduct comprised of thin subepithelial layer of circular fibres, followed by thin layer of longitudinal fibres.

Etymology.

The specific name is a composite of the Latin adjective niger (black) and the Latin noun margo (margin), referring to the colour pattern with dark margins.

Distribution.

Known only from its type locality.