Othelosoma laticlavium Sluys & Neumann

Sluys, Ronald, Neumann, Matthias, De Lima, Ricardo F. & Drewes, Robert C., 2017, Land flatworms (Platyhelminthes, Geoplanidae) of São Tomé: a first account on their diversity, with the description of five new species, Zootaxa 4221 (3), pp. 291-322 : 304-309

Othelosoma laticlavium Sluys & Neumann , sp. nov.

Material examined. Holotype: ZMA V.Pl. 7252.1, São Tomé Island, Caué district , Ribeira Peixe, Monte Carmo forest, 5 September 2014, coll. Francisco Azevedo, sagittal sections of the anterior part of the specimen on 12 slides; sagittal sections of the prepharyngeal part on 16 slides; sagittal sections of the pharynx region on 18 slides; sagittal sections of the copulatory apparatus on 21 slides.

Other material: ZMA V.Pl. 7253.1, São Tomé Island, Caué district , Ribeira Peixe, Monte Carmo forest, 28 October 2014, coll. Francisco Azevedo, sagittal sections of the anterior part on 21 slides; transverse sections of the prepharyngeal part on 18 slides; sagittal sections of the pharynx region on 13 slides; sagittal sections of the copulatory apparatus on 18 slides.

Etymology. The specific epithet is derived from the Latin laticlavius, having a broad stripe or band, and alludes to the median, orange band on the dorsal surface of this species.

Diagnosis. Othelosoma species with a black dorsal surface and a broad, median orange band. No retractor in the anterior portion of the body and neither a muscular sphincter in the copulatory apparatus. Penis papilla a slender cone. Elongated muscular seminal vesicle. Bursal canal communicates with vaginal duct shortly before the latter penetrates the mid-ventral wall of the copulatory bursa.

Description. Dorsal surface black with a mid-dorsal orange band ( Fig. 25 ). Margins of ventral surface pale yellow-orange, with a dirty-white creeping sole ( Fig. 26 ). The anterior tip has a pair of well developed eyes, each surrounded by an unpigmented halo. The preserved holotype measured 38mm in length and had a body width of 3mm. The other specimen, V.Pl. 7253.1, was approximately 50mm long. Narrow creeping sole, comprising between one-fourth and one-third of the total body width of sectioned specimens.

Subepidermal musculature consisting of a thin layer of circular muscle, followed by a thin layer of longitudinal muscle. Parenchymal longitudinal muscles well developed, particularly on the ventral side, where longitudinal muscles are present also dorsally to the ventral nerve cords. No retractor muscle in the anterior end of the animal.

The root of the cylindrical pharynx is placed halfway of the distance between the anterior tip and the posterior end of the preserved specimen. Pharynx length is approximately 1/18th of the total body length in the preserved specimen. Mouth located at about 56% of the distance between the anterior and the posterior tip. The position of the mouth in relation to the pharyngeal cavity is almost in the posterior fourth of the pharyngeal cavity. The mouth is located at about 3/4th of the distance between the root of the pharynx and the posterior wall of the pharyngeal cavity.

Pharyngeal pouch musculature composed of few layers of subepithelial circular muscles, followed by a single layer of longitudinal muscles ( Fig. 27 ).

Outer pharynx epithelium underlain by a strong layer of circular muscles, followed by layers of intermingled muscles with both circular and longitudinal fibres ( Fig. 27 ). The same configuration of muscle layers is present underneath the inner pharynx epithelium, lining the lumen, albeit that here the zone of muscles is thicker than the one underneath the outer epithelium ( Fig. 27 ).

In the holotype the first testes are located 5mm behind the ovaries and 7.5mm behind the centre of the brain. The testes extend posteriorly to the postpharyngeal region, approximately 2mm before the anterior end of the muscular seminal vesicle. The testes are located ventrally on either side of the body between the intestinal branches and the parenchymal muscle band that is located dorsally to the nerve cords. The shape of the testes follicles is oblong, the follicles occupying between 1/6th and 1/7th of the dorsoventral diameter in the postpharyngeal part of the body.

The sperm ducts run amongst the fibers of the layer of longitudinal parenchymal muscle located dorsally to the ventral nerve cords. The distribution of muscle fibers around the duct is irregular, being more abundant on the dorsal than on the ventral side. The sperm ducts run posteriorly to about 4/5th of the distance between the anterior and posterior end of the seminal vesicle and then rather abruptly turn antero-dorsally and run towards the seminal vesicle at an angle of approximately 45 degrees ( Fig. 28 ). Along this part of the sperm ducts, at several places masses of sperm have burst out of the ducts into the surrounding parenchyma. Having reached about the anterior third of the vesicle, the ducts start to run parallel to the seminal vesicle and the body surfaces and after a short while start approaching the most antero-ventral portion of the seminal vesicle, meanwhile decreasing in diameter. Hereafter each duct penetrates the strong coat of muscles surrounding the seminal vesicle, to open separately into the most proximal section of its lumen ( Fig. 28 ).

The elongated cylindrical seminal vesicle runs more or less paralell to the body surface, with only its anterior, proximal end being curved towards the vental body surface. It is surrounded by a very strong coat of circular muscles. Longitudinal muscles lie interspersed in the zone of circular muscles. The lumen of the seminal vesicle is rather broad and gradually narrows to become the ejaculatory duct. The latter stays rather broad and opens at the tip of the penis papilla ( Fig. 28 ). The lining epithelium of the ejaculatory duct is nucleated and stratified. A pseudostratified, nucleated epithelium lines the lumen of the seminal vesicle.

The penis papilla is a slender cone and is covered with a thin, nucleated epithelium. The penis papilla proper, i.e. from its point of insertion to the tip, measures in the holotype 650µm in length, while the seminal vesicle measures 2000µm in length.

Penis glands are mainly distributed dorsally of the root of the penis papilla as well as on the dorsal side of the seminal vesicle. Further, extra-penial glands are located ventrally of the root of the penis papilla. The glands of the seminal vesicle are distributed ventrally and dorsally to the whole seminal vesicle, albeit that they are ventrally more abundant on the anterior third of the seminal vesicle than on the posterior part ( Fig. 28 ). All these erythrophil glands discharge secretions more or less perpendicular to the anterio-posterior axis of the ejaculatory duct and the lumen of the seminal vesicle, or prostatic vesicle.

Male atrium lined with a nucleated epithelium, underlain with a subepithelial layer of decussate muscles. Female atrium is lined with circular muscles.

Gonopore located at about two-thirds of the distance between the anterior and posterior end of the specimen. Distance between mouth and gonopore approximately 8mm, i.e. 1/4th of the total body length in the preserved holotype specimen. The gonoduct is surrounded by a relatively strong, subepidermal layer of circular muscles.

The slightly dorso-ventrally elongated ovaries have a small diameter and are positioned above the ventral nerve cords, occupying between 1/5th and 1/6th of the dorso-ventral diameter of the anterior part of the body. They are positioned at approximately 1/8th of the distance between the brain and the root of the pharynx. The oviducts arise from the ventral sides of the ovaries. Oviducts run in posterior direction between the fibers of the parenchymal muscle band, dorsally to the nerve cords. Dispersion of the muscle fibers around the duct is irregular, more fibres to the dorsal than to the ventral side.

At a distance of about 150µm posterior to the gonopore of the holotype, the oviducts curve dorso-medially to open separately, albeit closely together, into the bursal canal ( Fig. 27 ). These oviducal openings are located at about 1/5th of the distance between the atrial opening of the bursal canal and its communication with the vaginal duct, close to the copulatory bursa. The oviducts receive the openings of shell glands before and after the communication with the bursal canal.

From the point where it receives the oviducal openings, in the holotype the bursal canal runs for about 200µm into antero-ventral direction to open into the atrium, about 420µm dorsally to the ventral surface (this section of the bursal canal corresponds to the so-called canalis anonymus). From the point of the opening of the oviducts, the bursal canal (this part corresponding to Beauchamp's canal) rises slightly into antero-dorsal direction for about 200µm, thereafter for a short distance curving into dorsal direction and then following its course more or less parallel to the ventral body surface for about 350µm. Hereafter it curves sharply into dorsal direction and after about 150µm opens into the vaginal duct. The latter opens, 120µm dorsally from the point of fusion with the bursal canal, through the ventral wall of the copulatory bursa; the lining epithelium of the vaginal duct extends for a short distance into the bursa ( Fig. 29 ).

In the holotype, from its opening into the bursa, the comparatively narrow vaginal duct runs into antero-ventral direction for about 600µm, at an angle of approximately 40 degrees. Hereafter it opens into the atrium at a position about 320µm dorsally to the ventral surface. No sphincter muscle is present around the vaginal duct ( Fig. 30 ).

Vaginal duct and bursal canal are lined with a nucleated, ciliated and pseudostratified epithelium. The musculature around the vaginal duct consists of a layer of circular muscles, followed by a layer of intermingled muscles. The musculature around Beauchamp's canal is similar to that of the vaginal duct, albeit that there are more decussate muscles present.

The canalis anonymus is surrounded by circular muscles.

In the holotype, the sac-shaped bursa measures about 800µm in anterior-posterior direction and about 800µm in dorso-ventral direction, thus occupying slightly less than 50% of the dorso-ventral diameter of the body in this part of the specimen ( Fig. 28 ). The bursa is lined with a well developed, pseudostratified, nucleated epithelium. The bursal musculature is composed of a weak layer of decussate fibres . A connection between the bursa and the intestine is present on the very lateral side of the bursa in the holotype specimen, whereas in V.Pl. 7253.1 such a connection could not be detected. At that location, the bursa of the holotype is filled with a densely blue and red staining mass that spills into the gut ( Figs 31, 32 ). Actually, an even larger mass of this substance is present in a large portion of the intestine immediately anterior to the bursa ( Fig. 31 ).

Distribution. The species is only known from the type locality ( Fig. 9 ).

Discussion. The following combination of anatomical characters present in O. laticlavium makes it hardly comparable with any other representative of the genus Othelosoma : (1) small penis papilla, (2) small bursa, (3) vaginal duct that communicates with the bursal canal shortly before the vaginal duct enters into the bursa, (4) no retractor in the anterior part of the body, (5) no muscular sphincter around the vaginal duct. Other species of the genus Othelosoma in which a retractor and a sphincter are absent, while a communication between vaginal duct and bursal canal is present, are: O. angolense , O. nigrescens , O. speciosum , O. lineaenigrum Sluys & Neumann , sp. nov., and O. duplamaculosum . However, O. speciosum differs from O. laticlavium in the presence of a unique feature among the currently known species of the genus, i.e. by having two ventral suckers at the anterior third of the body. In addition to the external differences discussed above, O. speciosum has an elongated, large bursa, contrasting with the small copulatory bursa of O. laticlavium .

Othelosoma nigrescens differs from O. laticlavium in the vertical orientation of its seminal vesicle, in the presence of a large penis papilla, and in the fact that its vaginal duct forms various diverticula before communicating with the atrium. None of these characters of O. nigrescens are present in O. laticlavium .

Othelosoma angolense shares with O. laticlavium the interesting feature of a connection between the bursa and the intestine. But in contrast to O. laticlavium , which has a black dorsal body surface with a mid-dorsal orange band and pale yellow margins on the ventral side, the dorsal side of O. angolense has two dark brown bands, while it has a grey-brown ventral surface. In addition to these external differences between O. laticlavium and O. angolense mentioned above, they also differ in anatomical features. The penis papilla of O. laticlavium is a slender cone, whereas the penis papilla of O. angolense is a broad cone. Further, the oviducts of O. angolense enter into the bursal canal shortly before this canal opens into the vaginal duct, shortly before the latter opens into the bursa. In contrast to this, in O. laticlavium the bursal canal receives the oviducal openings at between one-fourth and onefifth of its way between the atrium and its point of communication with the vaginal duct.

Other morphological differences in the reproductive system are that the proportion between the small bursa and the long seminal vesicle of O. laticlavium stands in contrast to the bursa and the seminal vesicle of O. angolense , in which these two parts have a similar size.

Othelosoma lineaenigrum (see below) differs from O. laticlavium in the presence of a long penis papilla, a Cshaped seminal vesicle, and a large bursa with a relatively low epithelium. Also the course of the vaginal duct and the bursal canal are different. In O. lineaenigrum the female ducts are running more or less parallel to the ventral body surface. In contrast to these features in O. lineaenigrum , the female ducts of O. laticlavium follow a vertical or sinuous course, while the thick-walled bursa is small, the seminal vesicle is horizontally orientated, and the penis papilla is small.

Othelosoma duplamaculosum is characterised by having the point of communication between the bursal canal and the vaginal duct halfway between the atrial and the bursal openings of the latter, whereas the bursal canal of O. laticlavium communicates with the vaginal duct shortly before the latter enters into the bursa. Further, O. duplamaculosum has two dorsal rows of irregular yellow-ochre spots, whereas O. laticlavium has a single middorsal orange band.

Figures

FIGURE 28. Othelosoma laticlavium. Holotype, sagittal reconstruction of the copulatory apparatus; anterior to the left.

FIGURES 25 – 27. Othelosoma laticlavium. Fig. 25. ZMA V. Pl. 7253.1, dorsal side of living specimen. Scale bar not available. Fig. 26. ZMA V. Pl. 7253.1, ventral side of living specimen. Scale bar not available. Fig. 27. ZMA V. Pl. 7253.1, sagittal section of the pharynx; anterior to the right.

FIGURES 29 – 32. Othelosoma laticlavium. Fig. 29. ZMA V. Pl. 7253.1, sagittal section of the penis papilla. Fig. 30. Holotype, sagittal section through the point of communication between copulatory bursa, vaginal duct and bursal canal. Fig. 31. Holotype, sagittal section of female copulatory apparatus and gut showing the densely staining mass; anterior to the left. Fig. 32. Holotype, sagittal section of the genito-intestinal connection; anterior to the left.

FIGURES 9 – 12. Fig. 9. Distributional records of terrestrial planarians used in this study. Red filled circle: Othelosoma lineaenigrum; blue filled triangle: Othelosoma duplamaculosum; purple filled square: Othelosoma impensum; brown filled hexagon: Othelosoma laticlavium; green filled asterisk: Othelosoma simile; black cross: Bipalium kewense. Fig. 10. Othelosoma impensum, holotype, drawing of anterior end of specimen in ethanol. Fig. 11. Othelosoma impensum, holotype, dorsal side of living specimen; scale bar not available. Fig. 12. Othelosoma impensum, holotype, ventral side of living specimen. Scale bar not available.