Lenopharynx bathos, Willems, Wim R., Sandberg, Maria I. & Jondelius, Ulf, 2007

Willems, Wim R., Sandberg, Maria I. & Jondelius, Ulf, 2007, First report on Rhabdocoela (Rhabditophora) from deep parts of Skagerrak, with the description of four new species, Zootaxa 1616, pp. 1-21 : 6-8

publication ID	https://doi.org/ 10.5281/zenodo.179102
DOI	https://doi.org/10.5281/zenodo.6252783
persistent identifier	https://treatment.plazi.org/id/039A0C4E-FFE7-FFA9-ECB2-CB29FDBDABAF
treatment provided by	Plazi
scientific name	Lenopharynx bathos
status	sp. nov.

Treatment

Lenopharynx bathos View in CoL sp. nov.

( Fig. 2 View FIGURE 2 A–D)

Locality. Loc. 4 (type locality).

Material. One animal studied alive and serially-sectioned (designated holotype; SMNH no. 7177).

Etymology. Species name refers to the depth of which the animal was collected. Bathos (Greek) : the depth of the sea, the deep.

Description. The almost globular animal ( Fig. 2 View FIGURE 2 C) is very small but could not be measured exactly. It is colourless and lacks eyes. The epidermis is 0,4 µm thick and carries 0,3 µm long cilia.

The pharynx ( Fig. 2 View FIGURE 2 D) is extremely long and slender and therefore has a snake-like appearance in live individuals. It is found in the rostral half of the body, with the mouth at approximately 70 %. No details regarding the mouth opening or the connection with the prepharyngeal cavity could be observed, because of damage to the ventral side of the body in the single serially-sectioned individual. The prepharyngeal cavity ( Fig. 2 View FIGURE 2 D: pc) is very deep (± 30 % of the pharynx length), lined with a very high, nucleated epithelium and surrounded by strong longitudinal muscles that act as pharynx protractors ( Fig. 2 View FIGURE 2 D: ppt). A circular muscle layer could not be discerned. The distal pharyngeal rim bears no cilia. The pharynx proper is surrounded by inner circular ( Fig. 2 View FIGURE 2 D: ecm) and outer longitudinal muscles ( Fig. 2 View FIGURE 2 D: elm). Internal musculature of the pharynx consists of radial muscles ( Fig. 2 View FIGURE 2 D: rm), a very weak longitudinal muscle layer ( Fig. 2 View FIGURE 2 D: ilm) and circular muscles ( Fig. 2 View FIGURE 2 D: icm). The exact numbers of these muscles could not be determined. At the distal end of the pharynx the internal circular muscles are stronger, forming a sphincter. The pharynx lumen ( Fig. 2 View FIGURE 2 D: pl) is lined with a high, frayed and anucleated epithelium. The pharynx contains two types of glands: one finegrained, eosinophilic and one fine-grained basophilic type both of which have an extra-pharyngeal part and enter the pharynx proximally. Both gland-types open near the distal end. About midbody, ventrally from the pharynx but not associated with it, a large bundle of both eosinophilic and basophilic glands is present.

The common genital pore ( Fig. 2 View FIGURE 2 B: gp) is situated at approximately 80%, just behind the mouth. It opens into a wide genital atrium ( Fig. 2 View FIGURE 2 B: cga) that receives the male system rostrally and the female system dorsally. The common genital atrium is surrounded by inner circular and outer longitudinal muscles and lined with a very low, anucleated epithelium. The circular muscle layer is very weak proximally. A vaguely delineated bursa ( Fig. 2 View FIGURE 2 B: bu) is situated caudodorsally of the genital atrium and opens into it through a short, muscular stalk ( Fig. 2 View FIGURE 2 B: bst). The male atrium ( Fig. 2 View FIGURE 2 B: ma) is surrounded by inner circular and outer longitudinal muscles and lined with a high, nucleated epithelium. The copulatory bulb proper is almost globular in shape and surrounded by inner circular and outer longitudinal muscles. The circular muscle layer is very thin and inconspicuous proximally and becomes gradually thicker distally. Before entering the copulatory bulb, both swollen and winding vasa deferentia ( Fig. 2 View FIGURE 2 B: vd) fuse, forming a short seminal duct. This duct, which can be closed by a strong sphincter, enters the copulatory bulb together with a bundle of course-grained basophilic glands and forms an internal seminal vesicle ( Fig. 4 View FIGURE 4 B: ivs). This vesicle opens into a separate compartment of the copulatory organ, together with fine-grained eosinophilic and course- and fine-grained basophilic prostate glands ( Fig. 4 View FIGURE 4 B: igg). This compartment is surrounded by weak circular muscles proximally and opens into the stylet that is associated with the copulatory bulb. The simple, straight stylet ( Fig. 2 View FIGURE 2 A, 2B: st) is slightly wider proximally and has a rounded distal tip. It is approximately 75 µm long (measured on a live individual).

A vit

t The paired, caudally situated ovaries ( Fig. 2 View FIGURE 2 B: ov) are oval in shape and each of them is connected to a swollen, sperm-filled seminal receptacle ( Fig. 2 View FIGURE 2 B: rs). The almost globular vitellaria ( Fig. 2 View FIGURE 2 B: vit) are connected to the seminal receptacles through separate wide vitelloducts that enter the receptacles dorsally. The narrow oviducts ( Fig. 2 View FIGURE 2 B: od) are surrounded by weak longitudinal muscles and leave the seminal receptacles ventrally. A sphincter is present near the middle of the oviducts, which fuse into a very short female duct. This duct enters the common genital atrium dorsally, where it can be closed by a very strong sphincter. A uterus ( Fig. 2 View FIGURE 2 B: ut) is present but its connection to the genital atrium could not be discerned.

Diagnosis. Lenopharynx bathos sp. nov.: colourless species of Lenopharynx without eyes and with a straight, tubular stylet, which is ca. 75 µm long, widened proximally and has a rounded distal tip.

Discussion. This species clearly is a member of Solenopharyngidae Graff, 1882 , as it shows the following diagnostic features: ventrocaudally-oriented, elongated pharynx, strongly-developed extrapharyngeal glands, a caudally-situated mouth, presence of a common genital pore, paired testes, intracapsular prostate glands and paired vitellaria (see Ehlers 1972).

This species closely resembles species of the taxon Lenopharynx Beklemischev, 1929 in the overall organisation of the genital system. This taxon includes three species: L. languidus Beklemischev, 1929 , L. triops Marcus, 1951 and L. tubatus Schockaert & Martens, 1985 , which are all characterized by the presence of a long snake-like pharynx, a bursa with a highly muscular bursal stalk, paired ovaries, two seminal receptacles and a male copulatory organ with an internal seminal vesicle.

Unlike L. languidus View in CoL and L. triops View in CoL , both species with an armed cirrus (see Marcus 1951; Beklemischev 1929; Ehlers 1972), L. tubatus View in CoL and L. bathos View in CoL are characterised by the presence of a simple, tubular stylet. However, the stylet differs in shape between the latter two species. In L. tubatus View in CoL it is not widened proximally and it has a straight distal edge, whereas the stylet of L. bathos View in CoL is wider proximally (almost cup-shaped) and has a rounded distal tip. Unfortunately, their lengths cannot be compared, as the stylet is not preserved in the holotype of L. tubatus View in CoL (see Schockaert & Martens 1985). Other differences between the two species are the presence of eyes and blackish-brown colouration found in L. tubatus View in CoL but missing in L. bathos View in CoL , which is colourless, transparent and lacks eyes.