Proceropharynx profundum, 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 : 8-10

Proceropharynx profundum sp. nov.

( Fig. 3 A–D)

Localities. Loc. 2 and Loc. 5 (type locality).

Material. Three animals studied alive. One whole-mounted specimen and two serially-sectioned individuals, one of them designated holotype ( SMNH no. 7178), the other one paratype ( SMNH no. 7179).

Etymology. Species name refers to the depth at which the animal was found and the fact that, until now, very few rhabdocoels were collected from such deep localities. Profundum (Latin) : the depth, the abyss.

Description. The relatively small animal is yellow and lacks eyes. The cellular epidermis is 0,6–0,8 µm thick with ± 0,4 µm long cilia.

The pharynx ( Fig. 3 A) is elongated and situated midbody with the mouth at ± 80 % (measured on sections). The prepharyngeal cavity ( Fig. 3 A: pc) is very narrow and lined with a nucleated epithelium. The distal part of the prepharyngeal cavity is tubular and can be closed by a weak sphincter, which is situated close to the mouth. Longitudinal muscles surround both the prepharyngeal cavity and the duct connecting it with the mouth. The external pharyngeal muscles consist of a weak, outer longitudinal ( Fig. 3 A: elm) and an inner circular muscle layer ( Fig. 3 A: ecm). Internal radial, circular and very weak longitudinal muscles ( Fig. 3 A: rm; icm; ilm) are present but their exact numbers could not be determined. Three types of pharyngeal glands, one of fine-grained, eosinophilic type and two of fine-grained (slightly different in grain-size), basophilic type enter the distal part of the pharynx. They all have a large extra-capsular part and enter the pharynx at its proximal end. Fine-grained eosinophilic glands (not indicated on Fig. 3 A for reasons of clarity) surrounded by strong longitudinal muscles are situated around the distal part of the pharynx bulb. It is unclear whether or not they enter the pharynx.

A

ivs vg ma vg ivs The gonopore ( Fig. 3 A: gp) is situated just behind the mouth in the most caudal part of the animal. Both the mouth and the gonopore lie very close together, but are not associated with each other. The gonopore leads to the common genital atrium ( Fig. 3 C: cga) which is lined with a high anucleated epithelium and surrounded by circular muscles. At the dorsal side of the genital atrium a more or less separate compartment ( Fig. 3 C: bc) is present. This so-called copulatory bursa (terminology of Ehlers 1972) is surrounded by a very strong circular muscle layer and lined with a high anucleated epithelium. Dorsocaudally an empty vesicle that could be the uterus ( Fig. 3 C: ut?), lined with a low anucleated epithelium and a resorptive bursa (cf. seminal bursa of Ehlers, 1972; Fig. 3 C: bu) enter the genital atrium very close to one another. The bursa is filled with sperm in different stages of resorption and both the bursa and the empty vesicle are distally surrounded by circular muscles. The genital atrium receives the male atrium ventrocaudally (through y on Fig. 3 C). A single oviduct enters the atrium from the caudal side.

The two testes are situated ventrocaudally and are not interconnected. The short vasa deferentia ( Fig. 3 D: vd) enter the male copulatory organ separately and lead into an internal seminal vesicle ( Fig. 3 B & D: ivs). This vesicle is surrounded by weak circular muscles. The globular copulatory organ and the small male atrium ( Fig. 3 B & C: ma) are surrounded by strong circular and weaker longitudinal muscles. The internal seminal vesicle opens into a compartment filled with course-grained, basophilic and fine-grained, eosinophilic secretion. The basophilic secretion is produced by glands in the upper part of the male organ. Fine-grained basophilic glands fill the rest of the male bulb. The distal part of the male organ consists of a long cirrus ( Fig. 3 B & D: ci) with small spines distally and hard ridges proximally (clearly seen on the live individual). In the sectioned material the cirrus is partially retracted, resulting in the spiny section being inverted into the section with ridges (see Fig. 3 D: ci)

The single, large ovary ( Fig. 3 C: ov) is situated caudally and connected with the common genital atrium through a short and narrow oviduct ( Fig. 3 C: od). The proximal part of the ovary and the resorptive bursa lie close together and are associated with each other through a broad and indistinct connection.

A large bundle of fine-grained, eosinophilic and fine-grained, basophilic glands ( Fig. 3 C: fg) open into the genital atrium, together with the oviduct. Vitellaria and vitelloducts could not be discovered.

Diagnosis. Proceropharynx profundum sp. nov.: species of Proceropharynx with a cirrus with small spines distally and ridges proximally; copulatory bursa small without hard structures.

Discussion. Proceropharynx profundum sp. nov. clearly is a member of the taxon Solenopharyngidae Graff, 1882 , and shows all diagnostic features of the taxon (see diagnosis in discussion of Lenopharynx bathos sp. nov.). Within the Solenopharyngidae the combination of a long ejaculatory duct with ridges and a very muscular copulatory bursa is only found within the taxon Proceropharynx Ehlers, 1972 . This taxon contains P. litoralis Ehlers, 1972 and P. anophthalmus Ehlers, 1972 , which have the same general organisation as P. profundum sp. nov. These two species are however colourless, have inter-connected rostrally-situated testes and ridges or lamellae on the cirrus. The presence of both hard ridges (on the proximal part of the cirrus) and small spines (on the distal part of the cirrus) is unique within the Solenopharyngidae .

Figures

FIGURE 3. Proceropharynx profundum nov. sp. A, reconstruction of the pharynx from the right side (from the holotype; radial muscles and gland necks in proximal part not shown for reasons of clarity). B, copulatory organ (from a live individual). C, reconstruction of the atrial organs from the right side (from the holotype). D, reconstruction of the male genital system (from the holotype).