Umbotectum, Sola & Sluys, 2023

Solà, Eduard, Sluys, Ronald, Riutort, Marta & Kawakatsu, Masaharu, 2023, Molecular phylogenetics facilitates the first historical biogeographic analysis of the hammerhead worms (Platyhelminthes: Tricladida: Bipaliinae), with the description of twelve new species and two new genera, Zootaxa 5335 (1), pp. 1-77 : 52-55

Umbotectum flagellum Solà & Sluys, sp. nov.

Synonym: Bipalium wiesneri: de Beauchamp, 1940: 115

Diagnosis

A small Umbotectum species characterized by a sickle-shaped head and an almost black ground colour, with a pale thin line encircling the head and at least one pair of pale transverse patches at the level of the pharynx. Penis papilla short and conical and provided with an invaginated flagellum. Wall of penial lumen with many, deep, rectangular folds. Penis bulb highly muscular and provided with three muscular zones: an inner zone of circular fibres, a thick middle zone of decussate fibres, and an outer zone of longitudinal muscle fibres. Dorsal part of female genital duct, with the shape of a mushroom cap, receives the separate openings of the oviducts at its most dorsal section. Lower portion of the female genital duct tubular, its middle section surrounded by an elongated sphincter made up of circular muscle. Male atrium and female genital duct openings into the common atrium at the centre of the moderately bulged roof of the atrium. Large spherical glands, or glandular crypts, located in the parenchyma of the bulged roof of the common atrium, irregularly arranged around the openings of the male atrium and the female genital duct; the glandular crypts or secretory reservoirs discharge into the common atrium.

Distribution

Umbotectum flagellum Solà & Sluys, sp. nov. is known only from the type locality, Mount Pulai, Johor, Malaysia.

Etymology

The specific epithet is derived from the Latin flagellum, whip, lash, and refers to the invaginated flagellum in the penial papilla.

Description

The single specimen available measured about 25 mm in length and 5 mm in width. Its auricles were rather long and highly recurved, suggesting that in the live animal the head is sickle-shaped ( Figure 26 ); in the preserved specimen the diameter of the rounded, disc-shaped head was 7 mm ( de Beauchamp 1940, Fig. 1 ). The dorsal side is almost black, with only a thin pale line following the outline of the head at a short distance from its margin, and a pair of pale transverse patches at the level of the pharynx ( de Beauchamp 1940, Fig. 1 ). Possibly, there are also two other pairs of transverse pale patches, but these were highly faded in the single specimen available. The ventral side was somewhat paler than the dorsal surface, while the creeping sole measured about 1/6 th of the width and is bordered by a somewhat denser pigmentation.

The penis bulb is long and elongated and consists of four zones: (a) the lining epithelium of the penial lumen is underlain by a thin parenchymatic zone, followed by (b) a zone of densely packed circular muscles, followed by (c) the major mass of the penis bulb, consisting of intermingled, decussate muscle fibres, which on its outer surface is bounded by (d) a zone of longitudinal muscles that is confluent with the thin layer of longitudinal muscle surrounding the male atrium ( de Beauchamp 1940, Pl. 27; Fig. 26 ).

The wall of the penial lumen, lined with a thin epithelium, is thrown into numerous large folds, forming more or less rectangular crypts.

The intromittent part of the penis, the penis papilla, has the shape of a small and slender cone. It is provided with a long invaginated, tubular flagellum resembling the flagellum in some species of Dendrocoelum Ørsted, 1844 , e.g. D. tubuliferum de Beauchamp, 1919 (see de Beauchamp 1919). The external epithelium of the penis papilla is underlain by a thin layer of circular muscles, followed by an equally thin layer of longitudinal muscles, which are continuous with those of the male atrium.

The major part of the male atrium is of a tubular shape; it communicates with the common atrium by means of an opening located in the mid-dorsal section of the bulged roof of the latter.

The female genital duct can be divided into three parts. The lower portion, which opens through the bulged roof of the common atrium, consists of a tall and rather narrow duct. The middle portion of this section is surrounded by a strong, elongated sphincter consisting of circular muscle fibres. The dorsal end of this tubular portion of the female duct pierces the ventro-left wall of the mushroom-shaped dorsal portion of the female genital duct. This mushroom-shaped cap of the female genital duct receives the separate openings of the oviducts at its most dorsal part, with the oviducal openings being located at the right-hand side of the apex of the cap.

The common atrium is narrow, with its roof being bulged in the shape of a dome turned upside-down. Large, rounded glands or glandular crypts are present in the parenchyma of the bulged roof of the common atrium. These glands are more or less circularly arranged around the separate but contiguous openings of the female genital duct and the male atrium in the centre of the bulged roof of the common atrium, with at least five of such crypts being present on either side of the median plane. The reservoir or lumen of the glandular crypts opens via a very narrow canal into the common atrium. The entire spherical gland is surrounded by a thin layer of muscles.

Discussion

De Beauchamp (1940) assigned his specimen to the species Bipalium wiesneri von Graff, 1899 on the basis of some characteristics of the morphology of the copulatory apparatus. However, in its external features, as well as its anatomy, this animal presents such considerable differences from the species described by von Graff (1899) that we consider de Beauchamp’s animal to represent a new species, which is here described under the name Umbotectum flagellum. The description presented above is based on the account provided by de Beauchamp (1940). Unfortunately, this worker did not provide information on the testes, the ovaries, and the course and openings of the sperm ducts into the penial lumen.

In contrast to the almost completely black dorsal surface of U. flagellum, von Graff (1899) described Bipalium wiesneri with a light greyish brown ground colour, with a tinge of red on the head, and a dorsal median band of a light yellow or sulphurous colouration, flanked by two diffuse black-brown stripes running from the “neck” to the tip of the tail ( von Graff 1899, Pl. X, Figs. 16–17 ). Clearly, this differs very much from the colouration of U. flagellum.

According to de Beauchamp, his specimen had the same elongated male organ, with a small conical penis papilla, and a penial lumen provided with many large folds, as documented for B. wiesneri . However, de Beauchamp already noted that in B. wiesneri the anterior portion of the bulbar lumen was different from his specimen, in that in B. wiesneri this part consists of a very tall, non-plicated epithelium that is densely packed with strands of secretion (M̧ller 1907, Pl. XIX, Figs. 5–6 ), whereas in U. flagellum, this part of the bulbar cavity or seminal vesicle is formed by a series of regular and parallel papillae loaded with small vesicular cells.

In addition, the specimen described by de Beauchamp, thus U. flagellum, has an inverted flagellum in its penis papilla, a structure that is absent in B. wiesneri . Further, the arrangement of the muscle layers around the penis bulb differs in these two species. In B. wiesneri the lining epithelium of the penial lumen is underlain by a parenchymatic zone, followed by longitudinal muscles, then circular muscles, and finally the major part consisting of a very thick layer of longitudinal muscles. In contrast, in U. flagellum the most prominent, major muscular zone is a thick zone composed of decussate fibres, which is thus fully absent in B. wiesneri .

M̧ller (1907) did not describe the globular glands located in the roof of the male atrium and de Beauchamp (1940) argued that this presumed omission was probably due to an oversight or to the small size of the bulged roof, or to a situation that these organs are inconstantly present or absent in the species. Although none of these hypotheses can be rejected with absolute confidence, the specimen described by M̧ller appears to be fully mature and, therefore, we believe that it really lacked the globular glands.

Although both B. wiesneri and U. flagellum have a sphincter around the “stalk” or tubular part of the female genital duct, other aspects of this duct differ between these two species. For example, in B. wiesneri it opens directly into a wide, egg-shaped dorsal part, whereas in U. flagellum there is first a short duct, which is not surrounded by the sphincter, that connects the ventral part of the female genital duct with a mushroom-shaped dorsal part.

Although geographical distribution may be a poor indicator of separate specific status, it is noteworthy that the two species show disjunct overseas geographical distributions, as B. wiesneri occurs in the environs of Bogor (Buitenzorg), West Java, Indonesia, while U. flagellum was found on Mount Pulai, Johor, Malaysia.

The external appearance of U. flagellum (almost black ground colour, with a thin whitish stripe on the head and at least one pair of transverse whitish patches) shows a great deal of resemblance with D. shipleyi ( von Graff, 1899) from central Sulawesi. Diversibipalium shipleyi was described as being pitch black, with on the anterior third of the dorsal body a median zone of irregular, frequently interconnected whitish specks; further, there is a thin whitish line encircling the margin of the head ( von Graff 1899, Pl. XIX, Fig. 17 ). Diversibipalium shipleyi also has large auricles, spanning a width of 7.5 mm. However, the length of its body is 69 mm and thus it is a larger species than the small species U. flagellum.

De Beauchamp (1940) described U. flagellum with one pair, and possibly two other pairs of transverse whitish, albeit faded, patches. It may be that this situation merely resulted from a greatly faded median zone of whitish patches, as described by von Graff (1899) for D. shipleyi , and that thus U. flagellum is a synonym of the former. However, certainty on this possibility can be achieved only once the copulatory apparatus has been examined of D. shipleyi -like animals from the type locality of this species, viz., Central Sulawesi.

The copulatory apparatus of U. flagellum shows some similarities with that of Bipalium virile M̧ller, 1902 in that the latter also has a very elongated, muscular penis bulb and a short, conical penis papilla. Further, the female organ is also broad on its dorsal part and narrows to form a duct before communicating with the tubular portion of the male atrium, while this part of the female genital duct is surrounded by a sphincter (M̧ller 1902; Pl. V, Fig. 1 ). However, in its external appearance and also in many details of its copulatory apparatus (e.g., the diameter and shape of the bulbar lumen) B. virile differs considerably from U. flagellum.

Figures

FIGURE 1. Approximate native distribution (in yellow) of the subfamily Bipaliinae, modified from von Graff (1899) and Ogren et al. (1992). Localities of new species described in the present paper are indicated with numbers: 1) Bipalium rhytidoantrum; 2) B. rugiantrum; 3) Humbertium ithorense; 4) Novibipalium rhynchophorum; 5) Umbotectum capitofalcatum; 6) U. t-maculatum; 7) U. flagellum; 8) Diversibipalium marginatanigrum; 9) D. castaneum; 10) D. cephalolacteum; 11) D. contortolineatum; 12) D. duplalaticlavium. Introduced species (present worldwide, excepting Antarctica) have been excluded from the map.

FIGURE 5. Bipalium rhytidoantrum. RMNH.VER.20257.1 (field number KSL2401). A and B. Photomicrographs of sagittal sections of the anterior part, showing various anatomical features; anterior to the right.

FIGURE 6. Bipalium rhytidoantrum. RMNH.VER.20257.1 (field number KSL2401). Sagittal reconstruction (A) and photomicrograph of sagittal section (B) of the copulatory apparatus; anterior to the right.

FIGURE 16. Novibipalium rhynchophorum. Photomicrographs of horizontal section of the right half of the head of specimens ZMA.V.Pl.3053.a (field number KSL2381.1) (A) and ZMA.V.Pl.3053.b (field number KSL2381.2) (B).

FIGURE 17. Novibipalium rhynchophorum. Dorsal (A) and ventral (B) views of live specimen.

FIGURE 26. Umbotectum flagellum. A. Drawing of the anterior part of the preserved specimen; modified after de Beauchamp (1940). B. Reconstruction of the copulatory apparatus; modified after de Beauchamp (1940). Asterisk (*) indicates the characteristic flagellum present in this species.