Diagnosis: Procerodes dohrni Wilhelmi, 1909 can be distinguished from its congeners by (1) absence of a copulatory bursa, (2) obliquely oriented, highly muscular penial papilla, and (3) vasa deferentia which unite in the penial papilla to form the ejaculatory duct.
Habitus: Preserved specimens up to about 3.5 mm long and 1.75 mm wide. The front end shows a pair of small auricles and the anterior body margin is convex. Behind the auricles the body shows a slight constriction, after which the body margins run parallel to the broadly rounded hind end. In living animals the auricles appear to be very distinct and are then better referred to as tentacles (cf. Chandebois 1954: Fig.1B). In preserved specimens these tentacles may still be present as small outbulgings of the body margin. The eyes are placed at some distance behind the tentacles and are set wide apart. The body lacks pigment.
The pharynx is about one-third of the body length. The outer circular muscle layer of the pharynx is well developed, and the inner circular muscle layer is about twice as thick. The mouth opening is situated at the hind end of the pharyngeal cavity.
The anterior ramus of the intestine extends anterior to the eyes and gives off a pair of preocellar lateral diverticula. The posterior rami of the intestine are not connected, neither by commissures (although medially directed diverticula may be present behind the copulatory apparatus), nor by being confluent in the hind end of the body.
Male Reproductive System
The testes are rather irregularly shaped follicles of varying size. They are situated between the intestinal diverticula and may occur at the proximal or distal portion of these branches. The testicular follicles are situated dorsally, but their ventral portion may extend to or even beyond the mid-line of the body. There are about 15 follicles on either side of the body, extending from the level of the ovaries into the hind end.
At the hind end of the pharyngeal pocket the vasa deferentia enlarge to form well developed false seminal vesicles, which narrow again while ascending towards the penis bulb. The ducts penetrate separately the antero-lateral surface of the bulb, but in the penis they run side by side. At about half-way the penis papilla the vasa deferentia unite to form the ejaculatory duct, which is lined with nucleate, ciliated cells. The distal section of the ejaculatory duct shows a somewhat taller lining epithelium, which is penetrated by the openings of penis glands. The glandular elements lie outside the penis bulb. The sections of the vasa deferentia inside the penis are surrounded by a relatively thick layer of circular muscles.
The penis consists of a well developed bulb and a strong, conical papilla. In general, the penis papilla has a ventro-caudal, oblique orientation and is lined with a flat, nucleate epithelium. The papilla is provided with a thick, subepithelial layer of circular muscles which entally is bounded by a much thinner layer of longitudinal muscles.
Female Reproductive System
The vitellaria are well-developed and extend from anterior to the ovaries into the hind end of the body. The follicles are situated between the intestinal diverticula and occupy the entire space between dorsal and ventral body surface.
The relatively small ovaries are situated directly behind the brain, just above the ventral nerve cords. The oviducts arise from the postero-lateral surface of the ovaries and follow their course backwards dorsally to the nerve cords. Posterior to the gonopore the oviducts curve medially and open separately into the distal end of the diverticulum of the bursal canal. This diverticulum receives the openings of shell glands.
The bursal canal arises obliquely from the atrium but does not communicate with a copulatory bursa, which is absent in P. dohrni. The canal is rather wide and lined with an infranucleate, ciliated epithelium; it is surrounded by a relatively thick, subepithelial layer of circular muscles and a somewhat thinner zone of longitudinal muscles. The shape of the bursal canal may differ somewhat between individuals: it may be either a straight tube with the same diameter over its entire length, or a tube of which the dorsal portion shows an expansion.
The eyes are devoid of a lens; the number of retinal cells in each eye cup could not be established.
Karyology: The chromosome complement described by Galleni et al. (1984) does not concern P. dohrni and specimens of P. lobata (Sluys 1987).
According to Wilhelmi (1909) P. dohrni occurs in the same habitat as P. lobata. But since Wilhelmi's observations on P.dohrni concerned a mixture of specimens of P. lobata and P. dohrni his statements on the ecology are not entirely reliable. Chandebois (1954) found that in the "calanques" near Marseille P. dohrni and P. lobata were separated ecologically and never found together. She found P. dohrni in small pockets of water under completely submerged stones. However, in the samples of P. dohrni from the "calanques" that I examined, I found occasional specimens of P. lobata. Further, immature specimens of P. dohrni were encountered also in samples of P. lobata from Corfu and Messina (Sluys 1987). Thus, ecological separation between the two species is not complete. The animals from sample ZMA V.Pl.767 were collected from a brackish spring almost at sea level.
Type locality: Naples, Italy. Procerodes dohrni is known from Naples (Wilhelmi 1909), near Marseille (Chandebois 1954, Material Examined), Tunis (Zghal and Tekaya 1980), Corfu and Messina (cf. Sluys 1987), and the Sea of Marmora. Wilhelmi (1918) reported P. lobata from the latter area but the specimens, ZMB 6024, appeared to be P. dohrni (Sluys 1987).
Material Examined and Type Material
Z.M.B.: Lectotype: 8279a+b, Naples, 1906, sagittal sections on 2 slides. Paralectotypes: 8280a+b+c, Naples, 1906, transverse sections on 3 slides; 8282, horizontal sections on 1 slide; 8281, sagittal sections on 1 slide; 8380, Naples, 1905, sagittal sections of 2 copulating animals on 1 slide; 8278, sagittal sections of 2 copulating animals on 1 slide; 8515, whole mount of 2 copulating animals; 8276, whole mount of 2 copulating animals.
Further material examined from Z.M.B.: 5372-1, Naples, 1905, sagittal sections on 1 slide; 5372-2, sagittal sections on 1 slide; 5372-3, horizontal sections on 1 slide; 6024-1, Sea of Marmora, Prinkipo, 19.05.1918, sagittal sections on 2 slides.
Z.M.A.: V.Pl.766, France, Cassis, 21.02.1979, sagittal sections on 1 slide; V.Pl.767.1, sagittal sections on 1 slide; V.Pl.767.2, transverse sections on 2 slides; V.Pl.767.3, horizontal sections on 1 slide; V.Pl.767.4, sagittal sections on 1 slide; V.Pl.767.5, sagittal sections on 1 slide; V.Pl.767.6, sagittal sections on 1 slide; V.Pl.767.7, horizontal sections on 1 slide; V.Pl.767.8, horizontal sections on 1 slide; V.Pl.767.9, sagittal sections on 2 slides; V.Pl.767.10, sagittal sections on 1 slide; V.Pl.767.11, sagittal sections on 2 slides; V.Pl.767.12, transverse sections on 1 slide; V.Pl.767.13, transverse sections on 2 slides; V.Pl.767.14, horizontal sections on 1 slide.