Polliculus cochlearis

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 : 20-22

Polliculus cochlearis n.g. n.sp.

( Figs. 8 B–8D)

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.

Playa Cerro Chato, Parque Nacional de Santa Teresa, Departamento de Rocha, Uruguay (33°59’6.34”S, 53°31’48.81”W). Sand a couple of meters from the waterline (± 30 cm deep) (31/07/2004).

Material. Two whole mounts, one of which designated paratype (HU no. 418). Two serially-sectioned specimens, of which one designated holotype ( SMNH 7500).

Etymology. The genus name refers to the French fairy tale Hop o' My Thumb (French: Le Petit Poucet) written by Charles Perrault. Polliculus (Lat.) : little thumb. The species name refers to the screw-shaped accessory stylet. Cochlea (Lat.): snail shell.

Description. This species is remarkably small, the entire body length being no more than 0.4 mm. The syncytial epidermis is ± 2 μm high, strongly ciliated and contains vacuoles. The cilia are about 1–3 μm high. The diameter of the vacuoles varies from 1–2 μm. The basal membrane is about 1/6 of the epidermis height thick. Round to oval nuclei, with a diameter of ± 2 μm, are scattered throughout the epithelium. Small basophilic rhabdites, with a diameter of less than 1 μm, are situated apically in the epidermal epithelium of the ventral side and the rostral part.

The mouth lies in the anterior part of the body. It is surrounded by a weak sphincter. The frontal pharynx doliiformis is exceptionally large and elongated, and measures about 1/3 of the total body length. The distal half of the pharynx is narrower than the proximal half. The prepharyngeal cavity is lined with an anucleated, membranous epithelium and surrounded by a longitudinal muscle layer. The oesophagus is surrounded by the glands of Minot. The brain lies dorsally from the pharynx, with two eyes situated in front of it.

The gonads are unpaired. The testis lies just behind the pharynx and is situated at the right-hand side of the animal. A broad vas deferens leaves the testis and widens distally to form a seminal vesicle. Both the vas deferens and the seminal vesicle are lined with a membranous epithelium. There are no muscles surrounding these structures. The seminal vesicle proximally penetrates the prostate vesicle, which is surrounded by strongly-developed circular muscles (conjuncta-type copulatory organ; terminology of Karling 1956a). Proximally in the prostate vesicle, the vas deferens remains very broad to form an intracapsular seminal vesicle (arrow in fig. 8D). Basophilic and eosinophilic prostate glands are present. The nuclei-containing parts of these glands are situated extracapsularly.

The stylet is a long, hollow tube with a length of 25–27 μm. It bends distally and ends in an asymmetrical, distally-widening apex. The proximal part is funnel-shaped. It receives the ejaculatory duct and the prostate secretion. Around the tubular stylet, an accessory stylet with an axial length of 41–52 μm is present. This accessory stylet is spirally-wound around the stylet proper. In the holotype and live animals, these proximal windings are close to each other, while the distance between these two stylets increases distally. The last distal winding ends in a sharp point at about the same level as the distal end of the stylet proper. In the paratype, the distal part of the accessory stylet is partly unwound and runs next to the stylet. Proximally, this accessory stylet receives the secretion of about four accessory glands that lie around the narrowed, distal part of the copulatory bulb. Dorsally from the stylets, a membranous epithelium connects to the prostate vesicle; it is lacking ventrally. This is probably the epithelium of the male genital atrium. This male genital atrium and the prostate vesicle are in their turn surrounded by another membranous epithelium that is proximally and distally encompassed by a well-developed, circular muscle layer (conjuncta-duplex type copulatory organ; terminology of Karling 1956a). The male genital atrium is at the left-hand side of the animal. Rostrally, it opens into the small common genital atrium, which is lined with an anucleated, membranous epithelium.

The female duct enters the caudal wall of the common atrium. It is relatively short, lined with a membranous epithelium and surrounded by a circular muscle layer. Small clumps of sperm are observed in the distal part of the female duct, which proximally receives the oviduct and the vitelloduct. The oviduct is also lined with an anucleated, membranous epithelium and surrounded by circular muscles. The single ovary is at 60% of the body length and lies roughly in the middle. Laterally, two vitellaria are present. These run rostrally at both sides of the pharynx and have a widened distal part. Distally, they join and open into the female duct through a common vitelloduct. An oviform seminal receptacle enters the common atrium caudally. This organ contains many sperm and is surrounded by a strongly-developed circular muscle layer. Its distal part is narrower, lined with a membranous epithelium and surrounded by a weak circular muscle layer.

Between the male atrium and the gonopore a uterus also enters the common atrium. The gonopore is situated at about 75% on the ventral side.

Discussion. The combined presence of the following features: one ovary, paired vitellaria, a frontal pharynx and a gonopore in the posterior part of the body, suggests the placement of Polliculus cochlearis n.sp. in the Dalyelliidae .

Polliculus cochlearis n.sp. clearly differs from every other species of dalyelliids in having only one testis and one vas deferens. In all other dalyelliids there are two. Moreover, the vas deferens of P. c o c h l e a r i s n.sp. forms a relatively large extracapsular vas deferens. Apart from this species, extracapsular seminal vesicles, one on each vas deferens, only occur in very few species: Gieysztoria dodgei ( Graff, 1911) Ruebush & Hayes, 1939 , Microdalyellia armigera ( Schmidt, 1861) Gieysztor, 1938 , Microdalyellia fusca ( Fuhrmann, 1894) Gieysztor, 1938 and Jensenia angulata ( Jensen 1878) Graff, 1882 (see Luther 1955). In Halammovortex Karling, 1943 , the vasa deferentia join in an unpaired, extracapsular seminal vesicle. None of these genera, however, has a muscular septum around the conjuncta-duplex type as does P. c o c h l e a r i s n.sp.

Within the Dalyelliidae, Luther (1955) distinguishes four types of stylet: the Microdalyellia (= armigera )- type, the Gieysztoria (= rubra)- type, the Castrella - type and the Axiola - type ( Axia - type in Luther 1955). The Microdalyellia -, Gieysztoria - and Castrella - types all consist of a common base on which a group of spines is implanted. The Axiola - type, in contrast, is a tubular stylet. It is found uniquely within the marine genus Axiola Luther, 1957 . The stylet of Polliculus cochlearis n.sp. thus could be considered as of the Axiola - type. The presence of an accessory stylet, however, is unique within the Dalyelliidae .

Polliculus cochlearis n.sp. also differs from all other species of Dalyelliidae by the lack of a so-called bursa copulatrix. This structure is a well-developed protrusion of the common genital atrium where sperm is also stored ( Luther 1955). Only in Vaillantiella algerica Luther, 1955 , is it rather indistinct. Another unique characteristic of P. c o c h l e a r i s n.sp. is the presence of a distinct uterus, opening in the rostral wall of the common genital atrium and with clear uterine glands. Such a uterus occurs in several rhabdocoels, but is lacking in all other species of Dalyelliidae , where the uterus is formed by a distal widening of the female duct ( Luther 1955). These considerable differences clearly warrant the erection of a new genus for the species from Uruguay.

Five genera of dalyelliids are known that are exclusively marine: Alexlutheria Karling, 1956 , Axiola Luther, 1957 , Beauchampiola Luther, 1957 , Halammovortex Karling, 1943 and Jensenia Graff, 1882 . Two other taxa, Gieysztoria Ruebush & Hayes, 1939 and Microdalyellia Gieysztor, 1938 , mainly include fresh water species, but also contain a number of species that occur in brackish habitats. The other known genera, Austrodalyellia Hochberg & Cannon, 2002 , Castrella Fuhrmann, 1900 , Dalyellia Gieysztor, 1938 , Fulinskiella Gieysztor & Szynal, 1939 , Sergia Nasonov, 1923 , Vaillantiella Luther, 1955 and Varsoviella Gieysztor & Wiszniewski, 1947 , only occur in fresh water.

Diagnosis. Polliculus n.g.: Dalyelliidae with pharynx in the first body half. Unpaired testis and ovary. Paired vitellaria. Vas deferens widened to an extracapsular seminal vesicle. Eosinophilic and basophilic prostate glands with extracapsular, nuclei-containing parts. Copulatory bulb with intracapsular seminal vesicle, prostate vesicle and male genital atrium with stylet. Screw-shaped accessory stylet wound around a long tubular stylet. Accessory stylet receives the secretion of four extracapsular accessory glands. Short female duct surrounded by circular muscles. Oviform seminal receptacle. Copulatory bursa absent. With distinct uterus. Type species: Polliculus cochlearis n.sp.

Diagnosis. Polliculus cochlearis n.sp.: provisionally, the same diagnosis as the genus. Stylet with a length of ± 26 μ m. Accessory stylet ± 47 μ m long.

Figures

FIGURE 8. Baicalellia forcipifera n. sp. (A) Habitus of a live animal. Polliculus cochlearis n. g. n. sp. (B) General organisation of an animal based on serial sections. (C) Stylet and accessory stylet (from the paratype). (D) Reconstruction of the atrial organs from the right side (arrow indicates intracapsular seminal vesicle).