(Schmidt, 1861)
Overview
Diagnosis: Procerodes lobatus (Schmidt, 1861) is characterized by the lack of pigmentation and by its prominent auricles. The species is anatomically characterized by fusion of the vasa deferentia in the dorsal portion of the penis bulb and by the separate openings of the oviducts in the diverticulum of the bursal canal.
Habitus: Live, mature specimens are 5-7 mm long and 0.50-1 mm wide. Body slender and elongated. Body margins nearly parallel, gradually tapering towards the front end; largest diameter at the hind region of the body. Well developed auricles. The front end of the body is slightly convex, and the hind end is rounded or obtusely pointed.
The body is devoid of pigment and, as a consequence, the intestine may be clearly visible, whereas the brain, part of the ventral nerve cords, testes and copulatory apparatus may show through the body wall. The eyes are situated posterior to the narrow neck region and are set wide apart.
Alimentary System
The pharynx is one-fourth to one-third of the body length and has an elongated and slender appearance. The root of the pharynx lies at about the middle of the body so that, consequently, the pharynx and the pharyngeal pocket comprise a large part of the posterior half of the body. The mouth opening is situated at the hind end of the pharyngeal pocket.
The anterior ramus of the intestine extends anterior to the eyes and gives off a pair of pre-ocellar diverticula. The intestinal rami may show in total 24-27 pairs of lateral diverticula on either side of the body, of which 9-11 pairs are given off by the anterior ramus (Lang 1881c, Böhmig 1906, Wilhelmi 1909). The lateral diverticula are not, or only infrequently, furcated. Occasionally, the posterior rami may show one or two commissures behind the copulatory apparatus.
Male Reproductive System
The testes are large rounded or oval-shaped follicles, situated dorsally, but usually extending considerably towards the ventral body surface. The follicles extend from the level of the ovaries into the hind end of the body. There are about 30 testes on either side of the body. The testes may show a rather regular, pairwise and pseudo-segmental arrangement, i.e. one follicle in each intestinal septum; in the hind end of the body the arrangement is usually more irregular.
The vasa deferentia form very large false seminal vesicles from about the posterior portion of the pharyngeal pocket up to the penis bulb. Behind the pharyngeal pouch the vasa deferentia turn dorso-medially and narrow before entering the penis bulb; shortly after having entered the bulb, the vasa deferentia fuse. The resulting common duct may narrow gradually towards the tip of the penis papilla or may first form a dilatation, i.e. a seminal vesicle, which subsequently narrows gradually to the ejaculatory duct. Penis glands discharge their secretion into the distal portion of the ejaculatory duct.
The penis usually is short and conical and has a vertical orientation.
The male atrium may be either narrow or more spacious; before opening in the common atrium the male atrium shows a prominent constriction.
The musculature of the penis bulb is weakly developed. The penis papilla is provided with a thin, subepithelial circular muscle layer and a thin layer of longitudinal muscle fibres. The ejaculatory duct is surrounded by a thin layer of circular muscles.
Female Reproductive System
The small ovaries are situated just above the ventral nerve cords, at a short distance behind the brain. The way in which the oviducts arise from the ovaries may differ between specimens. The duct may leave the ovary from its ventral surface or it may arise from the ventro-caudal or antero-ventral surface of the ovaries. In some specimens the oviducts may even extend anteriorly and communicate with a small secondary ovary (see also Wilhelmi 1909: 250). In running backwards, the oviducts follow closely the course of the ventral nerve cords; in the hind end of the body the ducts open separately into the diverticulum of the bursal canal.
The vitellaria are extensive, filling most of the space between the intestinal diverticula; the follicles occupy the entire space between dorsal and ventral body surface and extend from the level of the ovaries into the hind end of the body.
The copulatory bursa is rounded or has an irregular shape; it is lined with tall, vacuolated cells which rest on a well developed basement membrane. The bursa is surrounded by a well developed layer of intermingled muscle fibres. The bursal canal is surrounded by a subepithelial layer of circular muscles and a layer of longitudinal muscle fibres. The diverticulum, which receives the openings of shell glands, is only surrounded by a thin layer of circular muscle fibres.
Eyes
The eyes contain three retinal cells, whereas a lens is absent.
Reproduction
Karyology: A diploid complement of 14 metacentric chromosomes, gradually decreasing in size, has been assessed for specimens from the type locality, i.e. Corfu (Ball 1979). According to Galleni and Puccinelli (1979) the British population of Procerodes lobata is different from the Corfu population in that the first pair of chromosomes is submetacentric.
Life Cycle: The brown and rounded cocoons lack a pedicel. Their diameter varies from about 0.4 to 1 mm but averages about 0.7 mm. Under laboratory conditions cocoons may be laid the whole year through, but nothing is known about this behaviour under more natural conditions.
Procerodes lobatus may encapsulate in a thin, transparant and elastic capsule. These elongated capsules are about 1 mm long. The animals lie curled up in these capsules, their heads resting on the hind end of the body. The planarians are rather active and turn around in their capsules. Animals may show this behaviour of encapsulation under otherwise favourable laboratory conditions. Specimens leaving their capsules do not appear to be different from other, previously not encapsulated, animals. This behaviour was described already by Wilhelmi (1909), with the difference that he found the capsules to be rounded instead of elongate. Lus (1926) also observed this peculiar behaviour of P. lobatus. Since animals may encapsulate under favourable conditions and capsules evidently do not prevent desiccation, Wilhelmi (1909) was in doubt about the meaning of these capsules, and neither am I able to provide a functional explanation for this phenomenon.
Ecology
Procerodes lobatus lives near the water level in coarse sand and gravel, as well as under stones, up to a depth of about 50 cm. For the British population Den Hartog (1968) mentioned that the planarians feed on dead animals among the flotsam.
Distribution
Type locality: Corfu, near El Canon. The older distributional records are summarized by Wilhelmi (1908, 1909): Mediterranean and Adriatic: from Ganzirri (?) up to Faro (Portugal), Nice, Genova, Corfu, Naples, Amalfi (southeast of Naples), Messina (Sicily), Taranto, Trieste, Patras (Greece, Peloponnisos); Black Sea: Sevastopol, Yalta, Sukhumi. Wilhelmi (1918) reported the species from the Sea of Marmora but the animals collected (ZMB 6024) appeared to be P. dohrni (Sluys 1987). Chandebois (1954) recorded the species from Marseille, and Mack-Fira (1974) found P. lobata on the Romanian coast of the Black Sea, and Lus (1926) again near Sevastopol. Recently, the species has been reported again from Corfu (Ball 1979), whereas it was found also on Mallorca (Material Examined). The range of the species was extended by records from Plymouth (Den Hartog 1968, Galleni and Puccinelli 1979, Material Examined) and from the Gulf of Tunis (Zghal and Tekaya 1980).
Material Examined
Private collection Ian R. Ball: N59.1, Corfu, Benitsen, May 1978, sagittal sections on 1 slide; horizontal sections on 1 slide; N59.4, transverse sections on 2 slides; N60.1, Corfu, Mesonghi Beach, 8.05.1978, sagittal sections on 1 slide; N60.3, horizontal sections on 1 slide; laboratory population of specimens from Corfu (Benitsen).
Z.M.A.: V.Pl.614.1, Mallorca, mouth Torrente de Pareis, La Calobra, 2.01.1978, sagittal sections on 1 slide; V.Pl.649.2, Mallorca, Port de Vallemossa, 3.05.1983, sagittal sections on 1 slide; V.Pl.649.3, sagittal sections on 1 slide; V.Pl.649.4, sagittal sections on 2 slides; V.Pl.649.5, sagittal sections on 2 slides, V.Pl.649.6, sagittal sections on 1 slide; V.Pl.649.7, sagittal sections on 1 slide; V.Pl.719.1, Plymouth, Wembury, England, 17.09.1984, sagittal sections on 2 slides; V.Pl.719.2, horizontal sections on 1 slide.
Z.M.B: 8365, Sevastopol, 1906, one out of three whole mounts on 1 slide.
Type Material
No type specimen available.