Choeradoplana onae Lago-Barcia & Carbayo, 2021

Lago-Barcia, Domingo, Silva, Marcos Santos & Carbayo, Fernando, 2021, Revision and description of six species of Choeradoplana (Platyhelminthes, Tricladida), with an emendation to the genus, ZooKeys 1016, pp. 1-48 : 1

Choeradoplana onae Lago-Barcia & Carbayo sp. nov. Figures 16 , 17 , 18

Choeradoplana sp. in Álvarez-Presas et al. 2014.

Material examined.

All specimens collected in the Reserva Biológica Augusto Ruschi, Santa Teresa, State of Espírito Santo, Brazil (-19.88, -40.54) by F. Carbayo and co-workers, 25-27 May 2008; Holotype MZUSP PL 2270 (field code, F2414), transverse sections of the cephalic region on 8 slides; horizontal sections of the portion behind the cephalic region on 5 slides; sagittal sections of the ovarian region on 12 slides; horizontal sections of the testes on 10 slides; transverse sections of the pre-pharyngeal region on 9 slides; sagittal sections of the pharynx and copulatory apparatus on 12 slides; Paratype MZUSP PL 2267 (field code, F2230), transverse sections of the cephalic region on 8 slides; sagittal sections of the pharynx and copulatory apparatus on 9 slides; Paratype MZUSP PL 2268 (field code, F2281), sagittal sections of the pharynx and copulatory apparatus on 12 slides. Paratype MZUSP PL 2269 (field code, F2310), transverse sections of the cephalic region on 12 slides; horizontal sections of the ovarian region on 8 slides.

Distribution.

Only known from the type locality, Reserva Biológica Augusto Ruschi, Santa Teresa, State of Espírito Santo, Brazil.

Etymology.

The name Choeradoplana onae is the affectionate nickname of the biologist Marta Álvarez-Presas (Bristol University). The specific epithet honors her for her contributions to understanding the systematics of free-living flatworms.

Diagnosis.

Choeradoplana species with a light ivory background color and a wide sepia brown median band. The extrabulbar region of the prostatic vesicle has a dish-shaped portion. The copulatory apparatus is 3.8 × longer than its height. The male atrium has 4-6 main folds.

Description.

External aspect. Preserved specimens range between 41-44.5 mm in length and 3-4 mm (n = 4) in width. The body is slender and subcylindrical. The cephalic region is differentiated from the remaining body by a ‘neck’ and laterally dilated. This region is rolled up so that the ventral surface provided with two prominent glandular cushions is facing out when alive (Fig. 16A-C ); the posterior extremity is pointed. The creeping sole is as wide as 85-87% of body width at the pre-pharyngeal region (n = 4). The mouth is positioned at a distance from the anterior extremity equal to 51% of body length, and the gonopore is 61% (paratype F2230).

The dorsal coloration of live specimens consists of a light ivory (RAL 1015) background color (Fig. 16A ), covered on a wide median band with sepia brown pigment (RAL 8014), except for irregular clear spots with the background color exposed. The bordering line of the band merging with the background color on the sides is irregular with large sepia brown spots. The curled anterior extremity is red orange (RAL 2001). The ventral surface is red orange in the cephalic region, and light grey (RAL 7035) in the rest of body (Fig. 16B ).

The eyes are devoid of halos, and formed by a one-pigmented cup of 60 μm in diameter. Eyes are absent in the very anterior extremity of the body equivalent to 1% of the body length (n = 1). Eyes behind the anterior tip are distributed marginally in a row of two or three eyes (Fig. 5C ) and extend along the entire body until the posterior end.

Sensory pits are 20-25 µm deep in a uniserial ventro-lateral row, starting from 0.4 mm behind the anterior extremity, the equivalent of 1% body length to at least 80 mm from the anterior tip (20% of body length, n = 1).

Rhabditogen gland cells pierce the marginal epidermis in the pre-pharyngeal region. Erythrophil granules and scarce cyanophil granules are discharged through the entire epidermis. There is no glandular margin (Fig. 16D ).

The cutaneous musculature consists of a subepithelial circular muscle, followed by a diagonal layer with decussate fibers, and a strong longitudinal muscle organized in bundles (Fig. 16D ). This longitudinal muscle is 90-100 μm thick dorsally, and organized in tight bundles with> 32-60 fibers each; it is ventrally divided into a 30-32.5 μm-thick muscle organized in bundles with 5-11 fibers each, and a 75 μm-thick muscle sunken into the parenchyma, and constituted of bundles with 8-27 fibers each (Fig. 16D ). The thickness of the cutaneous muscle coat is 18-20% (n = 4) of the body height.

In the pre-pharyngeal region, there are three parenchymal muscles, namely a dorsal decussate muscle (40-50 μm thick), a transverse supra-intestinal muscle (15 μm); and transverse subintestinal muscle (18-20 μm) (n = 4) (Fig. 16D ).

The cutaneous and parenchymal musculature is organized in the cephalic region as in Ch. iheringi . The muscle retractor of the head is delta-shaped in a cross-section along 2.5 mm (or 6% of body length) from behind, 0.9 mm (or 2%) anterior extremity of the body (Fig. 16E ), and its thickness equals 19% of the height of the cephalic region. The Muskelgeflecht is 160-180 μm thick (23% of body height). The subneural parenchymal muscle consists of a number of transverse fibers; this muscle is weak in the ovarian region. Glandular cushions are composed of numerous rhabditogen cells (Fig. 16E ).

The mouth is located in the middle of the pharyngeal pouch (n = 4) (Fig. 17A, B ). The pharynx is bell-shaped with its dorsal insertion at mouth level (n = 4). The esophagus is as long as 15% of the pharyngeal length. The pharyngeal pouch is lined with a non-ciliated, low epithelium underlain by a one-fiber thick longitudinal muscle followed by a 10 µm-thick circular muscle. The outer pharyngeal epithelium is flat, ciliated, and underlain by a 5 µm-thick longitudinal muscle followed by a 15 µm-thick circular muscle. The inner pharyngeal epithelium is flat and ciliated, and is underlain by a mixed circular muscle with longitudinal fibers (80 μm thick). The pharynx has numerous interspersed erythrophil and xanthophil gland cells.

The testes are mature, dorsally located under the supra-intestinal transverse parenchymal muscle, placed between the intestinal diverticula. They extend from 13.2 mm (32% of body length, holotype) from the anterior extremity to 0.2 mm of the root of the pharynx (63%, holotype). Sperm ducts bend dorsally and medially immediately above the subintestinal parechymatic muscle layer to open into the respective dilated branch of the prostatic vesicle. The prostatic vesicle is divided into two halves (Fig. 17C ). The anterior half is extrabulbar and proximally presents a dilated and paired tubular portion oriented vertically which opens into a broadened, dish-shaped section located above the paired portion. This proximal half is lined by a columnar-to-cuboidal epithelium that is pierced by gland cells producing xanthophil granules. These gland cells are much more abundant in the dish-shaped portion and present a strongly reddish appearance; the ventral face and the border of this dish-shaped section of the prostatic vesicle is also pierced by gland cells producing cyanophil granules. The distal half is an intrabulbar dilated canal oriented dorso-posteriorly. It is lined by a columnar epithelium with a sinuous surface that is pierced by gland cells producing cyanophil granules along its whole length and additionally gland cells producing xanthophil granules in its distal portion. The lining epithelium of the proximal half of prostatic vesicle is coated by an 18-20 µm-thick circular muscle layer, while it is coated by a 1 µm-thick circular muscle in the distal half, followed by a 15 µm-thick longitudinal muscle (n = 4). The extrabulbar portion of the prostatic vesicle is coated by additional muscle fibers attaching it to the common muscle coat (Fig. 17D ). The opening of the prostatic vesicle into the antero-dorsal region of the male atrium is wide, without an ejaculatory duct or penis papilla (Fig. 18A-C ).

The male atrium is long, 5 × as long as the female atrium, with the same height along its length and 4-6 large transverse folds narrowing its lumen. The male atrium is lined by a cuboidal, non-ciliated epithelium, and is underlain by a 40-70 µm-thick circular muscle with numerous interspersed longitudinal fibers (n = 4). The proximal two thirds of the atrium receive two types of abundant gland cells producing xanthophil and erythrophil granules, respectively, and a third type of scarce gland cells producing amorphous xanthophil secretion; the distal third of the male atrium receives abundant gland cells producing erythrophil granules. The sub-apical portion of the cells of the lining epithelium of this distal third contains xanthophil granules.

The ovaries are mature, ovoid, 250 μm in length, placed above the ventral nerve plate and at a distance from the anterior tip of the body equal to 28% of body length (11.8 mm from the anterior tip) (n = 1). Ovovitelline ducts emerge from the dorso-lateral aspect of the ovaries and run ventrally. Ovovitelline ducts run medially and dorsally lateral to the posterior section of the female atrium, then unite above the postero-dorsal section of the female atrium (Fig. 18A-C ). The common glandular ovovitelline duct length ranges between 25-150 µm in length (n = 4) and runs ventrally or ventro-posteriorly to communicate with the female genital canal. This canal runs downwards, and subsequently penetrates the common muscle coat to open into the posterior section of the female atrium. The genital canal is lined by a cuboidal, ciliated epithelium, and the sub-apical portion of its lining cells is stained reddish.

The female atrium is funnel-shaped, and is lined with a 50 µm high epithelium, which is pierced by gland cells producing fine erythrophil granules. The subapical portion of the lining cells contains xanthophil granules. The lining epithelium of the female atrium is underlain by a 1-fiber-thick longitudinal muscle, followed by a 10 µm-thick layer of decussate muscle fibers. Paratype F2281 presents a female atrium smaller than that of the remaining specimens and also bears a spermatophore at the entrance of the gonopore canal. This spermatophore is ovoid, and with approximately 100 µm in maximum diameter. It is constituted on an inner mass of sperm surrounded by a thin fibrous, erythrophil layer, external to which is a gross layer of xanthophil, granular secretion and a bluish fine granular secretion, each prevailing on one side of the spermatophore (Fig. 18D ).

The common muscle coat is a very dense layer composed by variously oriented muscle fibers. The length:height ratio of the copulatory apparatus enveloped by the common muscle coat ranges between 2.5-3.3:1 (n = 3).

Remarks.

The species described herein matches all diagnostic characteristics of Choeradoplana . As reported for Ch. claudioi Lago-Barcia & Carbayo, sp. nov., Ch. onae Lago-Barcia & Carbayo, sp. nov. only resembles Ch. abaiba , Ch. agua , Ch. banga , Ch. iheringi , Ch. claudioi Lago-Barcia & Carbayo, sp. nov., and Ch. pucupucu in the body color. The great similarity between them hinders confident identification. However, none of them present the prominent cushions found in this species with a red-orange color.

With respect to the internal morphology, Ch. onae Lago-Barcia & Carbayo, sp. nov. only compares with Ch. riutortae Lago-Barcia & Carbayo, sp. nov. and Ch. bocaina in that they also present a dish-shaped prostatic vesicle. However, the length:height ratio of the copulatory apparatus in these species is 2.6:1 (vs. 3.8:1 in Ch. onae Lago-Barcia & Carbayo, sp. nov.); the male atrium:female atrium ratio in Ch. bocaina and Ch. riutortae Lago-Barcia & Carbayo, sp. nov. ratio ranges between 1:1-3:1 (Carbayo & E. M. Froehlich, 2012), whereas it is ~5:1 in Ch. claudioi Lago-Barcia & Carbayo, sp. nov. and Ch. onae Lago-Barcia & Carbayo, sp. nov., and the male atrium presents 1-2 large folds (vs. 4-6 in Ch. onae Lago-Barcia & Carbayo, sp. nov.).

Figures

Figure 5. Choeradoplana tristriata (Schultze & Mueller, 1857), specimen F 3226. Photomicrographs of sagittal sections A prostatic vesicle and the male atrium B female atrium. Abbreviations: cm common muscle coat, co common glandular ovovitelline duct, dd decussate dorsal cutaneous muscles, dm diagonal decussate muscles, e eye, ej ejaculatory duct, ep esophagus, er erythrophil secretion, fa female atrium, fd female genital duct, g gonopore, i intestine, lc longitudinal cutaneous muscles, ma male genital atrium, mk Muskelgeflecht (Graff, 1899), mo mouth, o ovary, ov ovovitelline duct, ph pharyngeal pouch, pp penis papilla, pv prostatic vesicle, px pharynx, rg rhabditogen glands, r retractor muscle, sb subintestinal transverse muscles, sd sperm duct, sg shell glands, sk sunken longitudinal cutaneous muscles, sm spermatophore, sn subneural transverse muscles, sp supra-intestinal transverse muscles, t testis, vi vitellaria, vn ventral nerve plate.

Figure 16. Choeradoplana onae Lago-Barcia & Carbayo, sp. nov. A dorsal view of the creeping live paratype F 2230 B live paratype F 2310 rolled up showing the ventral surface C lateral view of the cephalic region of live paratype F 2230 D photomicrograph of a transverse section of the pre-pharyngeal region of holotype E photomicrograph of a transverse section of the cephalic region of holotype. Abbreviations: cm common muscle coat, co common glandular ovovitelline duct, dd decussate dorsal cutaneous muscles, dm diagonal decussate muscles, e eye, ej ejaculatory duct, ep esophagus, er erythrophil secretion, fa female atrium, fd female genital duct, g gonopore, i intestine, lc longitudinal cutaneous muscles, ma male genital atrium, mk Muskelgeflecht (Graff, 1899), mo mouth, o ovary, ov ovovitelline duct, ph pharyngeal pouch, pp penis papilla, pv prostatic vesicle, px pharynx, rg rhabditogen glands, r retractor muscle, sb subintestinal transverse muscles, sd sperm duct, sg shell glands, sk sunken longitudinal cutaneous muscles, sm spermatophore, sn subneural transverse muscles, sp supra-intestinal transverse muscles, t testis, vi vitellaria, vn ventral nerve plate.

Figure 17. Choeradoplana onae Lago-Barcia & Carbayo, sp. nov. Photomicrographs of sagittal sections A pharynx of paratype F 2230 B pharynx and copulatory apparatus of holotype C prostatic vesicle of paratype F 2230 D prostatic vesicle of holotype. Abbreviations: cm common muscle coat, co common glandular ovovitelline duct, dd decussate dorsal cutaneous muscles, dm diagonal decussate muscles, e eye, ej ejaculatory duct, ep esophagus, er erythrophil secretion, fa female atrium, fd female genital duct, g gonopore, i intestine, lc longitudinal cutaneous muscles, ma male genital atrium, mk Muskelgeflecht (Graff, 1899), mo mouth, o ovary, ov ovovitelline duct, ph pharyngeal pouch, pp penis papilla, pv prostatic vesicle, px pharynx, rg rhabditogen glands, r retractor muscle, sb subintestinal transverse muscles, sd sperm duct, sg shell glands, sk sunken longitudinal cutaneous muscles, sm spermatophore, sn subneural transverse muscles, sp supra-intestinal transverse muscles, t testis, vi vitellaria, vn ventral nerve plate.

Figure 18. Choeradoplana onae Lago-Barcia & Carbayo, sp. nov. A photomicrograph of a sagittal section of the copulatory apparatus of paratype F 2230 B photomicrograph of a sagittal section of the copulatory apparatus of holotype C diagrammatic representation of the copulatory apparatus of paratype F 2230 D photomicrograph of a sagittal section of the entrance of the gonopore of paratype F 2281 housing a spermatophore. Abbreviations: cm common muscle coat, co common glandular ovovitelline duct, dd decussate dorsal cutaneous muscles, dm diagonal decussate muscles, e eye, ej ejaculatory duct, ep esophagus, er erythrophil secretion, fa female atrium, fd female genital duct, g gonopore, i intestine, lc longitudinal cutaneous muscles, ma male genital atrium, mk Muskelgeflecht (Graff, 1899), mo mouth, o ovary, ov ovovitelline duct, ph pharyngeal pouch, pp penis papilla, pv prostatic vesicle, px pharynx, rg rhabditogen glands, r retractor muscle, sb subintestinal transverse muscles, sd sperm duct, sg shell glands, sk sunken longitudinal cutaneous muscles, sm spermatophore, sn subneural transverse muscles, sp supra-intestinal transverse muscles, t testis, vi vitellaria, vn ventral nerve plate.