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Schmidt, 1861

Overview
Diagnosis: Cercyra hastata Schmidt, 1861 can be recognized by the following combination of features. The vasa deferentia unite to form a single duct which penetrates the penis bulb, the latter being provided with three types of muscular zones. Penis with well-developed stylet. Oviducts opening separately into bursal canal. Copulatory bursa small or absent.
Habitus: Live specimens up to about 7 mm and 1.75 mm wide (Wilhelmi 1909), whereas preserved animals may be up to 4.5 x 1.5 mm. The largest living specimen captured by Murina (1981) measured 5 x 1 mm.
The lanceolate body has its largest diameter at the hind end of the pharynx; the hind end of the body is broadly rounded, whereas the rounded front end is much narrower.
Characteristic is the broad band of pigment in front of the eyes. The coloration of the rest of the dorsal surface is rather variable. Pigment may be absent, or the dorsal surface may show a brownish to yellowish colour, the pigment being arranged in an irregular reticulate pattern. Two unpigmented spots near the pharynx indicate the position of the ovaries. The ventral body surface is unpigmented.

Alimentary System
The pharynx is situated in the posterior half of the body and measures between one-fifth and one-fourth of the body length. The inner circular muscle layer of the pharynx is much thicker than the outer circular muscle layer. The mouth opening is at the hind end of the pharyngeal cavity.
The anterior ramus of the intestine extends anterior to the eyes, without giving rise to preocellar diverticula. Behind the eyes the anterior gut trunk gives rise to 7-8 pairs of extensively branched lateral diverticula with broadly rounded tips. Each of the two posterior gut trunks gives off about 11 lateral diverticula. Behind the pharynx these gut trunks may also show median diverticula, some of which may be connected, thus forming commissures.

Male Reproductive System
The testes are situated dorsally, although in some specimens the follicles may extend for a considerable distance towards the ventral body surface. In other specimens some follicles may lie very close to the ventral surface because of space limitations. The total number of follicles varies between 100 to 130-140. The testes extend from just behind the brain into the hind end of the body, and are rather irregularly distributed.
The vasa deferentia unite immediately behind the pharynx to a long and winding common duct, which is expanded to form a false seminal vesicle. This common duct narrows considerably where it enters the penis bulb; once within the bulb the duct expands again to form a large, rounded or oval-shaped seminal vesicle, from the posterior surface of which arises the ejaculatory duct. The latter opens at the tip of the penis papilla.
The penis consists of a well developed, bean-shaped bulb and a cone-shaped papilla, both oriented parallel to the body surface. The penis papilla is covered with a flat, nucleate epithelium. The penis bulb and the proximal part of the papilla show a complex musculature, in which three layers may be distinguished. The major portion of the musculature consists of a zone of more or less circularly running and somewhat interwoven fibres, defining the shape of the penis bulb (cm1). At the periphery of the penis bulb the muscle fibres have a more or less longitudinal orientation and they are confluent with the longitudinal muscles of the atrium. A second well-defined layer of circular muscles surrounds the seminal vesicle and the narrow section of the common vas deferens in the penis bulb (cm2); this layer is continuous with the much thinner layer of circular muscles around the proximal section of the ejaculatory duct. The third zone of muscles is situated in the proximal part of the penis papilla and concerns radially running fibres (rm). Bundles of these fibres run from the seminal vesicle outward and their course is such that in the end they make up the major portion of the longitudinal muscle layer of the penis papilla. Further, the papilla is provided with a layer of circular muscles directly underneath the lining epithelium and a thin layer of longitudinal fibres, continuous with a similar layer around the atrium, which joins the longitudinal muscles originating from the radial muscle layer.
The particular arrangement of the radial muscles delimits a parenchymatic area for the major portion of the penis papilla. In this area the granular secretion of penis glands accumulates before being discharged into the ejaculatory duct. The penial glands lie outside the penis bulb. Böhmig (1906: 482) already noticed that the secretion in the dorsal part of the penis papilla shows an eosiniphilous staining property, but that the secretion in the ventral section of the papilla stains much weaker or hardly stains at all, whereas the ventral secretion also has a much more fine-grained composition. It is evident that two types of penis gland are involved.
The penis papilla is provided with a well-developed sclerotized stylet which frequently points into the bursal canal. The male atrium is just large enough to house the penis papilla and communicates with the genital canal, from which it is separated by a ring-shaped constriction.

Female Reproductive System :

The relatively large, rounded or oval-shaped ovaries are situated close to the pharynx. They lie at about two-thirds of the distance between the brain and the root of the pharynx; quite frequently the ovaries are close to the point of insertion of the pharynx. The germ centre is situated in a characteristic, more or less tube-shaped sac arising from the postero-medial wall of the gonads. The ovaries are situated dorso-medially to the ventral nerve cords.
The oviducts arise from the ventro-lateral wall of the ovaries and immediately thereafter the ducts bifurcate to an anterior branch and a posteriorly directed section, both of which run laterally to the ventral nerve cords. The anterior branch extends forwards to closely behind the brain, and communicates with the vitellaria. The posterior branches of the oviducts open, separately, into the bursal.
The vitellaria are well developed, extending from anterior to the testes into the hind end of the body, and occupying the entire space between the dorsal and ventral body surfaces.
The bursal canal opens into the posterior portion of the atrium; the posterior part of the duct is curved towards the dorsal body surface and communicates with the small copulatory bursa. The bursal canal is lined with a nucleate, ciliated epithelium and receives the secretion of shell glands ectally to the openings of the oviducts. The bursa is lined with vacuolated cells. It is not exceptional for the bursa to be completely absent.

Eyes
The pigment cups are devoid of a lens and contain three retinal cells.

Reproduction
Karyology: The chromosome portret of C. hastata from the Adriatic Sea (Porto Recanati) has been studied by Galleni and Puccinelli (1982). The diploid complement consists of 2n=14 (n=7) chromosomes. Three pairs of chromosomes are submetacentric, three other pairs are subtelocentric, whereas in one pair the chromosomes show an acrocentric centromere. Two pairs of chromosomes are easily distinguishable because of their great length, but it is more difficult to tell apart the other chromosomes because these decrease gradually in size.
Life Cycle: The brownish, oval-shaped or rounded cocoons are unstalked, and reach a length of about 0.75 mm (Wilhelmi 1909).
In the Gulf of Naples Wilhelmi (1909) observed cocoon laying in February, March, April, and May with peak production in March. According to Murina (1981) the Sevastopol population of C. hastata breeds throughout the year. The last-mentioned worker found that incubation time is affected by temperature, thus varying from 13 days in summer to 35 days in winter.

Ecology
C. hastata lives in the littoral zone throughout the year (Murina 1981) and occurs under stones and in coarse sand (Wilhelmi 1909, E. J. de Vries pers. comm.).

Distribution
Type locality: Corfu, Greece. The species has been collected from the following localities: Mediterranean Sea: Corfu, Napels, Nice, Banyuls, Port Vendres, Marseille, Villefranche, Toulon, Menton (Du Plessis 1907, Wilhelmi 1909), Rhodos (Material Examined); Adriatic Sea: Porto Recanati (Material Examined, Galleni and Puccinelli 1982, Gremigni and Nigro 1983); Black Sea: Sevastopol, Sukhumi, Istanbul (Wilhelmi 1909, Lus 1926, Murina 1981, Material Examined).

Material Examined
Z.M.A.: V.Pl.725.1, Porto Recanati, Adriatic Sea, sagittal sections on 1 slide; V.Pl.726.1, Lindos, Rhodos, Greece, 23.05.1982, sagittal sections on 1 slide; V.Pl.726.3, sagittal sections on 1 slide; V.Pl.726.4, horizontal sections on 1 slide; V.Pl.726.5, sagittal sections on 1 slide; V.Pl.726.6, sagittal sections on 2 slides; V.Pl.726.7, sagittal sections on 1 slide; V.Pl.726.8, horizontal sections on 1 slide.
Z.M.B.: 5373b, Naples, 1906, sagittal sections on 1 slide; 5373c+d, transverse sections on 2 slides; 8363a+b, transverse sections on 2 slides; 8354, sagittal sections on 1 slide; 8516, sagittal sections on 1 slide; 8358, horizontal sections on 1 slide; 8357, transverse sections on 1 slide; 8355, 8349, Naples, 1906, 3 whole mounts, each on 1 slide; 8517, 5373a, 8518, Naples, 1907, 3 whole mounts, each on 1 slide; 5371, 8474, 8475, Naples, 1908, 3 whole mounts, each on 1 slide; 8362, 8359, Corfu, 08.1906, 2 whole mounts, each on 1 slide; 8392, Corfu ?, Argostoli ?, whole mount on 1 slide; 8485a-d, Sevastopol, 1906, horizontal sections on 4 slides; 5374c, sagittal sections on 1 slide; 8484, transverse sections on 1 slide; 8483, sagittal sections on 1 slide; 5374b, transverse sections on 1 slide; 8470, 5374a, 8480, 8481, 8482, Sevastopol, 1906, 5 whole mounts, each on 1 slide; 5373-1, Naples, 1907, transverse sections on 2 slides; 5373-2, sagittal sections on 1 slide; 6025-1, Konstantinopel, 26.05.1918, transverse sections on 4 slides; 6025-3, sagittal sections on 1 slide; 6025-4, sagittal sections on 3 slides; 6025-2, Konstantinopel, 16.05.1918, sagittal sections on 2 slides; 4342-1, Sevastopol, sagittal sections on 1 slide; 5374-1, Sevastopol, 1906, sagittal sections on 1 slide; 5374-2, sagittal sections on 1 slide; 5374-3, horizontal sections on 1 slide.

Cercyra hastata