Vauclusia multistriata, Steenkiste, Niels Van, Volonterio, Odile, Schockaert, Ernest & Artois, Tom, 2008

Steenkiste, Niels Van, Volonterio, Odile, Schockaert, Ernest & Artois, Tom, 2008, Marine Rhabdocoela (Platyhelminthes, Rhabditophora) from Uruguay, with the description of eight new species and two new genera, Zootaxa 1914, pp. 1-33 : 24-26

Vauclusia multistriata n.sp.

( Figs. 9 C, 10)

Locality. La Coronilla, Departamento de Rocha, Uruguay (33°54’18.50”S, 53°30’39.30”W). Beach and mouth of the canal near hotel Parque Océanico: sand covered by a thin green layer of organic material and sand with organic material near a small pool in open contact with the ocean (01/08/2004): type locality.

Material. Observations on one live animal. One whole mount, designated holotype ( SMNH 7501). Two serially-sectioned specimens, of which one designated paratype (HU no. 363).

Etymology. The species name refers to the many internal ridges of the stylet. Multus (Lat.): many. Striatus (Lat.): striated.

Description. Slender, 0.5 mm long animal. Eyes absent. The habitus is characterized by division of the body into three zones: a slender, rostral part where rhabdite glands occur (± 1/5 of the body length), a middle part where all organs are situated (± 3/5 of the body length), and a caudal part, which consists of a clearlydelimited, small tail with an epidermis containing many more rhabdites than the rest of the body (± 1/5 of the body length).

The ciliated epidermis is cellular and has a height of about 3 μm. The basal membrane is very thin. The cilia measure about 3 μm. In the rostral part of the body, two different kinds of rhabdite glands occur. The first type produces long, lancet-shaped, basophilic rhabdites with a length of 8–10 μm, the other type produces smaller, oval, eosinophilic rhabdites with a length of about 2–3 μm. Both kinds of glands extend from above the brain to the rostral body end, where they empty. Caudally from the pharynx, dispersed eosinophilic rhabdite glands occur, which empty in the epidermis. The largest concentration of these rhabdite glands is situated behind the genital system in the caudal body part. The length of the oval, eosinophilic rhabdites that are secreted by these glands varies between 2–4 μm. The epidermis of the caudal region is completely filled with these rhabdites.

The mouth is situated at about 40%. The organisation and structure of the pharynx is identical with that of Vauclusia conica Willems et al., 2004 (see Willems et al. 2004).

The gonads are paired. The two round testes are situated ventrally, just in front of the pharynx and at both sides of the body. The seminal vesicles are rather small and have an anucleated, membranous epithelium. They are not surrounded by muscle layers. When entering the prostate vesicle, both vasa deferentia join to form a ductus ejaculatorius, which runs centrally through the prostate vesicle. Centrally, this prostate vesicle contains coarse-grained, eosinophilic glands, which are surrounded by fine-grained eosinophilic glands. All glands together take up about half of the total volume of the prostate vesicle. Both the fine-grained and coarse-grained eosinophilic glands have extracapsular nuclei-containing parts, and penetrate the prostate vesicle together with the ejaculatory duct. The prostate vesicle is surrounded by thick, inner circular muscles and outer longitudinal muscles. Distally, the prostate vesicle is connected with a conical and thin-walled stylet. This stylet has a length of 45 μm. Proximally, it is 21 μm broad at its broadest, distally up to 4 μm. The inner side of this stylet is ornamented with a large number of ridges that are oriented in three different directions. For the first 17 μm, the ridges run lengthways, the next 7 μm they run transversely and the last 21 μm again lengthways. The male genital atrium is surrounded by circular muscles and is lined with an anucleated, membranous epithelium, as is the common genital atrium. The common gonopore is situated at about 70%.

The ovaries lie caudally from the gonopore and together with the more rostrally-situated vitellaria, they form long ovovitellaria, which stretch dorsolaterally at both sides beyond the testes. The oviducts are very short, and open in the long, very muscular female duct, which caudally enters the common genital atrium. It is lined with a high, anucleated epithelium and surrounded by a circular muscle layer, which is very well developed in the proximal half. Distally, it is slightly swollen and some nuclei are seen in the somewhat higher epithelium of the transition zone between the female duct and the common genital atrium. Moreover, the distal half of the female duct is surrounded by a peripheral, longitudinal muscle layer. The female bursa is spherical and lined with a nucleated, membranous epithelium. It contains a great deal of sperm in the lumen. A broad bursal stalk connects the bursa with the proximal end of the female duct. Its epithelium is very high and shows many glands. Where it enters the bursa, a sphincter is present. In the proximal part of the female duct, sperm and a glandular secretion were observed. Eosinophilic and basophilic female glands enter this part of the female duct. A uterus is lacking.

Discussion. The species described here can easily be placed in the taxon Vau c lu s ia Willems et al., 2004 because of the combined presence of the following characters (see Willems et al. 2004): pharynx in the middle of the body, paired testes and seminal vesicles, spherical prostate vesicle and two types of glandular secretions, conical stylet with different internal ridges, a long male atrium, paired ovovitellaria, a long muscular female duct with a swollen distal part, and the presence of a female bursa and female glands. The construction of the pharynx and the position of the testes are comparable with those of V. conica Willems et al., 2004 , the only other representative of the taxon, although in V. multistriata n.sp. the pharynx is situated somewhat more anteriorly.

A first important difference between the two species occurs in the size of the stylet and the pattern of its ridges. Although Vauclusia conica is almost three times as long as V. multistriata n.sp., its stylet is smaller than the stylet of V. multistriata n.sp. The exact structure of the stylet in V. conica could not be ascertained, but it apparently has about eight spirally-running and striated ridges ( Willems et al. 2004). In contrast, the stylet of V. multistriata n.sp. has many ridges, transverse as well as longitudinal. Secondly, the prostate glands of V. c o n i c a take up the full volume of the prostate vesicle, which is not the case in V. multistriata n.sp. Another difference is the presence of a bursal stalk with a glandular epithelium between the bursa and the female duct in V. multistriata n.sp. In V. conica , the bursa links up directly with the proximal part of the female duct through a sphincter. Finally, V. conica has an inversion of the muscle layer in the transition zone between the common genital atrium and the male atrium.

Some of the features that are unique to Vauclusia conica were mentioned in the original diagnosis of this genus by Willems et al. (2004), but now these features should be removed from this diagnosis.

Amended diagnosis (after Willems et al. 2004). Va u cl u si a: Promesostomidae with the pharynx in the middle of the body. Paired testes and seminal vesicles. Spherical prostate vesicle with two types of secretions. Conical stylet with several internal ridges. Paired ovovitellaria. Very long, muscular female duct. Distal part of the female duct swollen. Female bursa and female glands present. Male atrium long.

Diagnosis. Vauclusia multistriata n.sp.: species of Va uc lu s ia with a 45 μ m-long stylet with many internal ridges that run lengthways proximally and distally, and transversely in between. Prostate glands only fill a portion of the prostate vesicle. Duct with glandular epithelium between the bursa and the female duct.

Figures

FIGURE 9. Lurus evelinae Marcus, 1950 (A) Habitus of a live animal. (B) Stylet. Vauclusia multistriata n. sp. (C) Habitus of a live animal.