Itaipusa sbui 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 : 449-452

Itaipusa sbui Willems & Artois n. sp.

( Fig. 4 )

Locality. iSimangaliso Wetland Park, Sodwana Bay, Jesser Point (lighthouse) (27°32'28.4"S, 32°40'47.9"E), green algae from swirl holes on a rocky plateau in the mid-eulittoral of a highly-exposed, steep beach, December 10, 2009 (type locality).

Material. Several animals studied alive. One whole mount, designated holotype ( SMNH, type-8855) and two serially-sectioned individuals, designated paratypes (HU, nos 577–578).

Etymology. Species named after Sibusiso “Sbu” Mfeka (Ezemvelo KZN Wildlife), whose help was indispensable during collection of most of the material in this study.

Diagnosis. Species of Itaipusa with an ovoid copulatory bulb connected to an armed cirrus with two transversal bands of lamellar spines, the distal one U-shaped and the proximal one figure-eight-shaped. Female system with seminal receptacle, muscular 'receptacle bursa' consisting of two compartments and globular bursa with muscular bursal stalk. Large sphincter and bundle of glands present at the transition between female duct and common genital atrium.

Description. The animals are colourless, ± 1 mm long (measured on the whole mount) and have two eyes. The epidermis is syncytial, 3–5 µm thick, carrying 2–5 -µm-long cilia. A few sensory bristles surround the opening of the proboscis sheath. Rhabdites are elongated, rod-shaped and are absent from the region around the opening of the proboscis sheath, where the epidermis is more densely stained.

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. 4 B: sph). Proximally from the sphincter, a strong internal circular muscular layer is present. The proboscis sheath ( Fig. 4 B: ps) is surrounded by an inner circular and an outer longitudinal muscle layer. The epithelium of the sheath lacks nuclei in its narrow, distal part, whereas they are present in its proximal part, with the largest nuclei in the contact zone between sheath and cone epithelium. There are three pairs of integument ( Fig. 4 B: iret) and at least three, but most probably four, pairs of proboscis retractors ( Fig. 4 B: pret), as in most koinocystidids ( Brunet 1972). The exact number of dilatator and protractor muscles could not be determined ( Fig. 4 B: dil and prot).

The globular pharynx 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, with only the brain and eyes in between them. The narrow prepharyngeal cavity is lined with a low, anucleated epithelium and is surrounded by an inner circular and an outer longitudinal muscle layer, the former lacking proximally and becoming stronger towards the mouth. The pharynx lumen and the distal rim of the pharynx bulb are lined with a membranous, anucleated epithelium. The internal circular muscle layer is weak, whereas the external one is very strong. Radial muscles are weak and sparsely distributed. The exact number of internal, longitudinal and radial muscles could not be determined. A pharynx mouth sphincter is absent. At least three types of glands are present. Fine-grained, basophilic ( Fig. 4 B: phg1) and coarse-grained eosinophilic glands ( Fig. 4 B: phg2) are most probably opening into the pharynx lumen at some distance from the distal rim. Coarse-grained, basophilic glands ( Fig. 4 B: phg3) open very close to this rim.

Male and female gonads are paired. The elongated testes lie ventro-laterally, just behind the pharynx, and extend to the most proximal part of the copulatory organ. The elongated, kidney-shaped to ovoid ovaries are situated in the caudal third of the body with their proximal part directed caudally. The vitellaria flank the testes, but are situated medio-dorsally.

The common genital pore, situated subterminally at approximately 95%, can be closed by a strong sphincter and opens into the common genital atrium, which is distally lined with a high nucleated epithelium, proximally transitioning to a frayed epithelium without nuclei. The atrium is surrounded by an inner weak circular and outer longitudinal muscle layer. Close to the genital pore a rosette-shaped bundle of small, fine-grained, eosinophilic glands ( Fig. 4 C: gl) opens into the atrium. It receives the uterus and the male genital system anteriorly, the former more ventrally than the latter. The female genital system opens into the atrium from the dorsal side, together with a bundle of large, coarse-grained, basophilic glands ( Fig. 4 C: fg).

The paired seminal vesicles are lined with a high, nucleated epithelium and are surrounded by a circular muscle layer. They fuse upon entering the duplex-type copulatory organ (terminology of Karling 1956), forming the ejaculatory duct. This ovoid duct is 108 µm long and 72 µm wide at its broadest point (measured on the whole mount), which is situated at approximately half of its length. The surrounding septum consists of an inner circular and an outer longitudinal muscle layer. Three types of glands accompany the ejaculatory duct: the first type of glands ( Fig. 4 C: pg1) is extracapsular with filiform gland necks entering the copulatory organ proximally and producing coarse-grained, basophilic secretion; a second type of glands ( Fig. 4 C: pg2) is intracapsular and produces coarse-grained, eosinophilic secretion that is released into the ejaculatory duct together with the first type; a third type of glands ( Fig. 4 C: pg3) is indistinguishable from the first type, but is situated entirely intracapsularly. The ejaculatory duct is surrounded by circular muscles and lined with a pseudocuticular epithelium. More distally the epithelium is replaced by pseudocuticular lamellar spines, which are organised in two separate bands ( Fig. 4 D). These bands are clearly visible on live and whole-mounted material, but hard to distinguish on sectioned specimens. The more proximal band of this armed cirrus is 116 µm long, has the appearance of a twisted figure eight and consists of ± 5-µm-long lamellae. The more distal band is clearly U-shaped, 58 µm long and consists of ± 3-µm-long lamellae. The ejaculatory duct is connected to the male atrium, which is lined with a rather high, anucleated epithelium and surrounded by inner circular and outer longitudinal muscles. The latter are a continuation of the muscle layers forming the septum of the duplex-type copulatory organ.

The oviducts are rather short and swollen, filled with sperm and lined with a high, anucleated epithelium. Distally, they are surrounded by circular muscles and open into the proximal part of the female duct ( Fig. 4 C: sr; seminal receptacle of Karling, 1980), most probably together with the common vitelloduct. This part of the female duct is filled with sperm and probably functions as a resorptive vesicle. It is surrounded by a circular muscle layer and can be closed distally by a very strong, symmetrical sphincter ( Fig. 4 C: sph2), which is situated at the transition with the so-called ‘receptacle bursa’ ( Fig. 4 C: rbu1 and rbu2; distal part of the female duct; terminology of Karling 1980, but also see Reygel et al. 2011). The latter is entirely surrounded by a syncytial tissue ( Fig. 4 C: syn) and consists of two parts: a globular, sperm-filled part proximally ( Fig. 4 C: rbu1) and a tubular part distally ( Fig. 4 C: rbu2). Both parts are lined with a low, anucleated epithelium and surrounded by a strong circular muscle layer, which becomes a very large sphincter ( Fig. 4 C: sph1) consisting of broad lamellar circular muscle fibres. Proximally to this sphincter, the female duct (i.e. ‘receptacle bursa’ and seminal receptacle) receives a muscular bursal stalk ( Fig. 4 C: bs; primary bursa of Karling 1980), which is connected to a globular bursa ( Fig. 4 C: bu), filled with sperm (resorptive vesicle of Karling 1980). The stalk is surrounded by circular muscles and lined with a low, anucleated epithelium.

The uterus ( Fig 4 C: ut) is surrounded by an inner, weak, circular to spirally-running muscle layer and an outer longitudinal layer and lined with a high, nucleated epithelium. Distally, just before opening into the genital atrium, it receives a single type of coarse-grained, basophilic secretion.

Discussion. This new species of Itaipusa Marcus, 1949 possesses all diagnostic characters of the taxon, as given by Karling (1980) and, slightly amended, by Reygel et al. (2011).

The taxon Itaipusa consists of 15 known species. Whereas I. biglandula Reygel et al., 2011 has an unarmed penis papilla and I. scotica ( Karling, 1954) Karling, 1978 and I. sophiae ( Graff, 1905) Karling, 1978 have an armed penis papilla, all other 12 species possess a long and armed cirrus. Only five of these 12 species, i.e. I. acerosa ( Brunet, 1972) Karling, 1978 , I. divae Marcus, 1949 , I. karlingi Mack-Fira, 1968 , I. similis ( Brunet, 1972) Karling, 1978 and I. spinibursa Karling, 1978 , have a spiny cirrus that is not accompanied by any large hooks (see Karling 1980). The cirrus spines can be arranged in longitudinal bands, as in I. acerosa , I. similis and I. spinibursa ( Brunet 1972; Karling 1978, 1980), or in transversal bands, as in I. divae , I. karlingi ( Marcus 1949; Mack-Fira 1968; Karling 1980) and I. sbui n. sp. The number of transversal bands and their shape clearly differ among the three latter species. Whereas at least three parallel bands are present in I. divae (see Reygel et al. 2011: fig. 3B), I. karlingi possesses two U-shaped bands ( Mack-Fira 1968) and I. sbui n. sp. has one U-shaped and one figure-eightshaped band.

A striking feature in the female system is the presence of a 'receptacle bursa' (terminology of Karling 1980), which is defined as the most distal part of the female duct. It is swollen, highly muscular and separated from the proximal part of the female duct, which functions as a seminal receptacle, by a strong sphincter ( Reygel et al. 2011). A 'receptacle bursa' occurs in Brunetia camarguensis ( Brunet, 1965) Karling, 1980 , and in five species of Itaipusa : I. evelinae ( Marcus, 1954) Karling, 1980 , I. karlingi , I. ruffinjonesi Karling, 1978 , I. sbui n. sp. and I. spinibursa . In the latter species, its wall is provided with some spines, whereas the new species is the only one in which it is clearly divided into two different parts.

Furthermore, the female duct of I. sbui n. sp. is characterised by the presence of a giant sphincter, distally from the opening of the bursal stalk and at the transition to the common genital atrium. Such a sphincter, at exactly the same location, is only found in I. karlingi ( Mack-Fira 1968; Karling 1980). In I. acerosa and I. similis a sphincter is present, but its exact location is unclear. It is probably located on the most distal part of the bursal stalk, very close to or at the transition with the female duct ( Brunet 1972; Karling 1978, 1980). A similar-sized sphincter is located on the bursal stalk proper in I. renei Reygel et al., 2011 and I. biglandula (see Reygel et al. 2011). For three species of Itaipusa , I. bispina Karling, 1980 , I. curvicirra Karling, 1980 and I. sophiae , literature is unclear whether or not a sphincter is present.

All species with a sphincter on the female duct or the most distal part of the bursal stalk (i.e. I. sbui n. sp., I. karlingi , I. acerosa and I. similis ), also show a bundle of glands opening into the female duct, very close to the transition with the common genital atrium ( Mack-Fira 1968; Brunet 1972; Karling 1978, 1980).

Figures

FIGURE 4. Itaipusa sbui n. sp. A. General organisation (from a live specimen, completed with observations on sectioned material). B. Reconstruction of the proboscis and pharynx from the right-hand side. C. Reconstruction of the atrial organs from the right-hand side (B – C from a paratype). D. Copulatory organ (from the holotype).