Bhambathorhynchus abursalis Willems & Artois

Willems, Wim R., Reygel, Patrick, Steenkiste, Niels Van, Tessens, Bart & Artois, Tom J., 2017, Kalyptorhynchia (Platyhelminthes: Rhabdocoela) from KwaZulu-Natal (South Africa), with the description of six new species, Zootaxa 4242 (3), pp. 441-466 : 446-449

Bhambathorhynchus abursalis Willems & Artois n. gen. n. sp.

( Fig. 3 )

Locality. iSimangaliso Wetland Park , Lake St. Lucia estuary, detritus-rich, fine-grained sand taken from the land side of a sandbank that cuts off the estuary from the Indian Ocean, December 16, 2009 (type locality).

Material. Several animals studied alive. One whole mount, designated holotype ( SMNH, Type-8854) and two serially-sectioned individuals, designated paratypes (HU, nos 575–576).

Etymology. The genus name is dedicated to Bhambatha kaMancinza (ca. 1860–1906?), a Zulu chief of the amaZondi clan in present-day KwaZulu-Natal, famous for his role in an armed rebellion against the British. The species name refers to the absence of a (primary) bursa, which is present in most other koinocystidids.

Diagnosis. Bhambathorhynchus n. gen. Genus of Koinocystididae with proboscis of the typical koinocystidid construction with a proboscis juncture sphincter; pharynx without a mouth sphincter; prepharyngeal cavity with rostrodorsal bulge. Two seminal vesicles. Ovoid copulatory organ with filiform prostatic gland ducts; wall of male atrium with two large, bent hooks, each one connected to a muscular bulb. Female duct consisting of a proximal seminal receptacle and a distal ‘receptacle bursa’, the latter divided into two sections; female system without sphincters. Copulatory bursa absent.

Type species (by original monotypy): Bhambathorhynchus abursalis n. sp., provisionally with the same diagnosis as the genus. Hooks of male system 29–35 µm long.

Description. Unpigmented animals, ± 1.9 mm long (measured on the whole mount) with two eyes. The epidermis is cellular, 2–3 µm thick with 2–3-µm-long cilia. Rhabdites are very small and hard to discern on sectioned material.

The proboscis is approximately 1/6 of the body length long and of a typical koinocystidid construction (see Brunet 1972; Karling 1980), with a very strong Itaipusa - type proboscis juncture sphincter ( Fig. 3 A–B: sph). This sphincter is part of a layer of strong circular muscles, which are present over most of the organ’s length. The proboscis sheath ( Fig. 3 B: ps) is surrounded by an inner circular and an outer longitudinal muscle layer. Nuclei are present in the sheath epithelium in its distal part and in the contact zone with the cone epithelium. The retractor system consists of three pairs of integument ( Fig. 3 B: iret) and four pairs of proboscis retractors ( Fig. 3 B: pret). The exact number of dilatator ( Fig. 3 B: dil) and protractor ( Fig. 3 B: prot) muscles could not be determined.

The pharynx appears globular on live animals, but is pear-shaped in sections. It is inclined forwards, has a diameter of ± 1/7 of the body length and is situated in the first third of the body, closely behind the proboscis. The narrow prepharyngeal cavity is lined with a low, nucleated epithelium and surrounded by an inner circular and an outer longitudinal muscle layer. On the dorsal side, the cavity shows a small bulge ( Fig. 3 C: y) in which the epithelium is more densely stained (glandular?) and nuclei are concentrated. The pharynx lumen and the distal rim of the pharynx bulb are lined with a membranous, anucleated epithelium. Internal and external circular muscles are very strong. Radial muscles are distributed evenly (on sagittal sections) and number 48 (on horizontal sections). The same number of internal longitudinal muscles is present. A pharynx mouth sphincter is absent. Three types of pharynx glands are present. Coarse-grained, eosinophilic glands ( Fig. 3 C: phg1) open into the pharynx lumen proximally from the distal rim. Fine-grained, eosinophilic ( Fig. 3 C: phg2) and coarse-grained, basophilic glands ( Fig. 3 C: phg3) open into the prepharyngeal cavity near the distal pharynx opening. The latter type of glands (phg3) also has very few, slender gland necks opening into the pharynx lumen (not shown in Fig. 3 C) together with the coarse-grained, eosinophilic glands ( Fig. 3 C: phg1). A large bundle of eosinophilic glands surrounds the proximal pharynx opening (Minot glands, Fig. 3 C: gm).

Male and female gonads are paired. The elongated testes lie ventro-laterally, and extend from the level of the pharynx to the ovaries. The elongated, ovoid ovaries are situated at approximately 60% and are directed ventrocaudally. The short and narrow vitellaria are situated medio-dorsally from the testes, with a large distal bulge running ventrally towards the ovaries. The vitelloducts proper bend towards the dorsal side, but the exact location of their opening into the female system could not be observed.

The common genital pore is situated subterminally at approximately 95% and can be closed by a strong sphincter. It opens into the common genital atrium, which is lined with a high, nucleated epithelium and surrounded by an inner circular and outer longitudinal muscle layer. The tubular atrium receives the ventrallysituated uterus anteriorly. The male and female genital systems open into the atrium from the dorsal side, the former ventrally from the latter. The proximal part of the female system lies ventrally from the male system, whereas the most distal part lies dorsally from it. For reasons of clarity, the position of the proximal part of the female system is altered to a slightly more dorsal position in Fig. 3 E.

The paired seminal vesicles are lined with a high, nucleated epithelium and are surrounded by a circular muscle layer. They fuse just before entering the ovoid copulatory organ, forming the ejaculatory duct, which is lined with a nucleated epithelium. Its exact course through the copulatory organ is hard to discern, but more-or-less marked by the filiform gland necks of the coarse-grained, basophilic prostate glands, of which the glandular bodies with nuclei are situated extracapsularly. The copulatory organ proper is surrounded by a strong, inner circular and a weak, outer longitudinal muscle layer. Ventro-distally to the opening of the ejaculatory duct, two prominent muscle bulbs ( Fig. 3 E: mb) are present, each of them attached to a slightly-bent hook ( Fig. 3 D, 3E: mh). These hooks are probably outgrowths of the basement membrane of the male atrium, as indicated by the presence of a pseudocuticularised network connecting their bases (see Fig. 3 D). The hooks are 29 and 35 µm long, with their distal tips pointing away from each other. The tubular male atrium is lined with a membranous, anucleated epithelium and surrounded by an inner circular and an outer longitudinal muscle layer.

The oviducts are very long and thin, and not surrounded by any muscles. They are lined with a rather high, nucleated epithelium, making the lumen invisible on sectioned material. Slightly distally from the junction of the oviducts, the female duct ( Fig. 3 E: fd = sr + rbu1 + rbu2) widens and is surrounded by a prominent, inner circular and an outer longitudinal muscle layer. Its most proximal part is lined with a high, nucleated epithelium and shows a narrow, sperm-filled lumen ( Fig. 3 E: sr; seminal receptacle of Karling 1980). The remainder of the muscular female duct (i.e. the ‘receptacle bursa’ of Karling 1980) consists of two parts: a sperm-filled proximal globular part ( Fig. 3 E: rbu1) and a distal tubular part ( Fig. 3 E: rbu2). Both parts are lined with a low, anucleated epithelium and surrounded by the above-mentioned muscle layers, although the inner circular one appears to be considerably weaker around the globular part. Only the distal tubular part is surrounded by a syncytial tissue. Typical koinocystidid sphincters are lacking over the entire course of the female duct, as is a typical bursa with distinct resorptive vesicle and bursal stalk (see Reygel et al. 2011; primary bursa of Karling 1980).

The uterus is rather atypical, lacking the large mass of glands present in other koinocystidids. It is lined with a high, frayed and nucleated epithelium, and distally surrounded by inner circular and outer longitudinal muscles. About halfway along its length, the uterus receives some small, diffuse glands, producing a fine-grained, basophilic secretion.

Discussion. The new species shows all features of the taxon Koinocystididae , as given by Karling (1980), except for the presence of a strong sphincter around the female duct, distally from the seminal receptacle. However, the female duct does show a clear constriction at this location. Furthermore, a (copulatory) bursa consisting of a muscular bursal stalk with or without a resorptive vesicle (terminology of Reygel et al. 2011; primary or copulatory bursa with or without resorptive vesicle of Karling 1980) is missing in this species. This condition is already mentioned by Karling (1980) as rather exceptional for koinocystidids, and it appears that the only other species in which this structure is missing, is Tenerrhynchus magnus Brunet, 1972 ( Brunet 1972; Karling 1980).

Furthermore, the presence of large hooks in the absence of an armed cirrus is also uncommon within Koinocystididae and only occurs in Brunetia camarguensis ( Brunet, 1965) Karling, 1980 and Getula uncinata ( Karling, 1978) Karling, 1980 . Both taxa clearly differ from B. abursalis n. gen. n. sp. in the shape of the hooks, the detailed organisation of the copulatory bulb and the overall structure of the female system. Indeed, apart from the fact that B. abursalis n. gen. n. sp. is the only one of these three taxa that lacks a true copulatory bursa (see above), it is also the only one of the three that lacks a sphincter between the seminal receptacle and the rest of the female duct (see Brunet 1965; Karling 1978, 1980 for the details on the other two taxa). B. abursalis n. gen. n. sp. also differs in the fact that the ejaculatory duct distally ends dorsally from the two hooks, whereas in G. uncinata and B. camarguensis it ends in between both hooks. In addition, G. uncinata also lacks a proboscis juncture sphincter, which is present in both B. abursalis n. gen. n. sp. and B. camarguensis .

The above-mentioned, specific combination of features is clearly unique within the taxon Koinocystididae , and does not allow a placement of our specimens in any existing genus.

Figures

FIGURE 3. Bhambathorhynchus abursalis n. gen. n. sp. A. General organisation (from a live specimen completed with observations on sectioned material). B. Reconstruction of the proboscis from the left-hand side. C. Reconstruction of the pharynx from the left-hand side (B – C from a paratype). D. Hooks in male genital system (from the holotype). E. Reconstruction of the atrial organs from the left-hand side (from a paratype; proximal part of female system is moved dorsally for reasons of clarity).