THE GENUS Plesiophysa , WITH A REDESCRIPTION OF P . ornata

A redescription of conchological and anatomical characters of the planorbid mollusc Plesiophysa ornata (Haas, 1938) is presented, based on topotypic material and specimens from 14 additional localities in the Brazilian states of Rio Grande do Norte, Paraíba, Sergipe, Bahia, Espírito Santo and Minas Gerais. Due to the close similarity of their shells, a sure discrimination of the five species of Pl i physa described so far ( P. pilsbryi, P. granulata, P. guadeloupensis , P. ornata and P. hubendicki ) is only possible through their anatomical features. The present study points to the high probability of synonymy of P. hubendicki with P. ornata. Investigations on the anatomy of P. pilsbryi and P. guadeloupensis are needed to define their taxonomic relation with the other nominal species.

Cette charmante espèce se distinguerait nettement de toutes les autres par ses stries transverses, si elle n'en différait pas encore par la convexité de ses tours et sa spire des plus obtuse.
Nous en devons la connaissance à M. Ferdinand de Candé; seulement nous ne savons pas positivement si elle est de la Martinique ou de Cuba."Aguayo (1935) proposed the substitute name Plesiophysa pilsbryi for Orbigny's species, after verifying that its denomination was preoccupied by Physa striata Menke, 1830.
So far only a species of Plesiophysa was recorded in continental South America.It was named Physa (?Plesiophysa) ornata by Haas (1938), who described its shell characters, emphasizing that its general shape is that of Bulinus rather than of Physa, and that its placing under the latter genus was due to the absence of Bulinus in South and Central Americas.However, he acknowledged the impossibility of ranging his species together with the other American physae in the absence of anatomical data, and ascribed it provisionally to the subgenus Plesiophysa owing to the spiral striation of the shell.Bequaert & Clench (1939), on the basis of radular characteristics, and "until more of the soft anatomy is known", placed Plesiophysa in the Planorbidae as a distinct subfamily Plesiophysinae.In their paper the radula of P. ornata is described and figured.
The snails dissected for anatomic study were collected in 1960-1961.Since at that time we used no relaxing agents, the following protocol was adopted.A specimen freely moving about, with its head and foot well exposed, is carefully picked up with a forceps, so as to prevent it from retracting back to the shell.The shell aperture is kept upward, and the snail is gradually plunged into hot water at about 70°C for a time proportional to the animal's size (approximately 30 seconds for snails about 10 mm in shell length or diameter).If the shell is plunged to the level of the aperture for the first 15 seconds, the animal usually will not retract and then, after being completely submerged, will die.Care must be taken not to exceed the suitable temperature and time of immersion, since blood and tissue cooking would hinder dissection.The dead animal is plunged into cold water and gently pulled by the head-foot with a small forceps, so as to disconnect the insertion of the columellar muscle.The whole animal is then drawn out of the shell, which remains unbroken and filled with water, which dilutes the blood residuum avoiding its putrefaction within the shell.The animal is fixed in slightly modified Railliet-Henry's fluid (distilled water 930 ml, sodium chloride 6 g, formalin 50 ml, glacial acetic acid 20 ml), where it must remain for at least 24 hours before dissection.One change of the fixative after the first 24 hours is advisable.The amount of fluid should be not less than 10 times the volume of material to be fixed.The radulae are separated from the buccal mass by digestion in a vial with 10% NaOH (left overnight in the incubator at 56°C).They are then rinsed in tap water and mounted in a drop of glycerin on a microscopic slide, with the dorsal (toothed) surface upwards as in the living animal.
Voucher specimens are deposited in the Malacological Collection of the Oswaldo Cruz Institute.

DESCRIPTION
The egg capsule (Fig. 1) is shaped like a flattened subovate disc, resembling that of other planorbids.The shell of hatchlings (Fig. 2) has spiral rows of hairy projections, which tend to disappear as the animal grows.
The adult shell (Figs. 3, 4) is sinistral, elongato-ovate, from pale amber to deep brown, with 3 to 3.5 rapidly expanding whorls separated by a deep suture.It varies in color and translucency according to the degree of saturation or incrustation with environmental material.The outer whorl is exceedingly swollen, as compared with the inner ones.The spire is most often flattened, sometimes sub-acute, and shows various degrees of elevation beyond the general curve of the surface.The aperture is very wide, elongato-ovate, and corresponds to 60%-75% of the whole shell length.The lip is very thin and the columellar fold reflects over the umbilicus.In some specimens the newly formed and still uncalcified border has a membranous consistency and shrinks after desiccation.The outer surface is sculptured with fine spiral striae, which intercross with the growth lines.In many specimens residual rows of hairy projections may be seen, usually confined to the proximity of the suture.Our largest shell is 9 mm long and 5 mm wide.
The exposed soft parts are light gray, excepting the head and the axis of the tentacles, which are deeply pigmented.The tentacles are slender and very extensible.The foot is oblanceolate.
The roof of the pulmonary cavity is irregularly pigmented black, leaving many irregular spots unpigmented.Internally it is widely occupied by the renal organ (Fig. 5), which extends from the left of the heart to the region of the pneumostome; from there it bends on itself to reach the heart auricle, turns again in a sharp curve to descend along the right margin of the previous loop, and finally bends leftward to open inside the mantle aperture.A small vesicle, lying on the right side of the heart, exactly corresponds to that described as "pericardial organ" by Harry & Hubendick (1964) in Plesiophysa granulata.A dorsolateral ridge runs on the left of the renal organ, reflecting ventrally at the back of the pulmonary cavity to proceed cephalad as the rectal ridge.
As in most planorbid genera, the mouth is provided with a large superior jaw, striated vertically, and two smaller lateral jaws (Fig. 6).The radular formula of eight specimens varied from 16-1-16 to 22-1-22, there being 107 to 120 transverse rows of teeth in the radular ribbon.Fig. 7 shows a series of radular teeth.The central tooth has a sharp triangular cusp and two or three small cusps high on either side of the main one.There are 6 to 8 laterals, 3 to 5 intermediates and 6 to 12 marginals.The laterals are squarish, tricuspid, with a small accessory cusp between the endocone and the mesocone, and another one lateral to the ectocone, sometimes also between the mesocone and the ectocone.The intermediates show interstitial cusps between the endocone and the mesocone and small cusps above the ectocone.The mesocone persists in the earlier marginals, flanked on both sides with smaller cusps.The extreme marginals are claw-like with about five small cusps.
The remaining digestive system is shown in Fig. 8.The salivary glands pass through the nerve ring and are joined to each other behind.The disposition of the digestive organs does not substantially differ from that in other planorbid genera, except for the position of the anterior intestinal loop between the stomach and the albumen gland.The anal opening is situated at the dorso-caudal base of a lappet (Figs. 8,9,10,al) under the pseudobranch, corresponding to the "anal lobe" shown by Hubendick (1949, Fig. 15, an.l.).
The pseudobranch (Figs. 8,9,10,pb) is represented by two much folded lanceolate leaves which in the live animal are usually held as shown in Fig. 4.
The oviduct is short and crooked, continuing into a voluminous nidamental gland that suddenly narrows into a convoluted uterus followed by a short vagina.The spermatheca varies in shape with the amount of its contents, showing a usually rounded or ovoid body partly embedded in the wall of the nidamental gland, and a duct about as long as the body emptying near the vaginal opening.The spermiduct extends alongside of the nidamental gland down to the level of the spermatheca.The prostate consists of 2 to 7 club-shaped, unbranched to trifurcate diverticula emptying into a separate duct, which joins the spermiduct to form the vas deferens.The penial complex is topped by a retractor muscle and two short flagella, equal or unequal in length, sometimes split, which are glandular organs emptying their secretion into the penis sheath.The penis sheath, about a third as long as the prepuce, is encircled by eight glands at its distal end, and contains a verge somewhat longer than it, with a subterminal opening and a cuticularized tip.The prepuce, much wider than the penis sheath, is provided with retractor and protractor muscles.Hubendick's (1949Hubendick's ( , 1955) ) investigation on the anatomy of P. ornata was impaired by unsatisfactory preservation of the material available to him.He studied the proximal portions of the alimentary canal (jaw, teeth and salivary glands), the pseudobranch, the kidney, and the distal parts of the reproductive system: uterus, vagina and spermatheca, and penial complex.In two points his observation differs from the present one: he describes the prostate as "constituted by a large number of fold formations directed outwards from the vas deferens", and the outlet of the penial canal as "terminal".In our specimens the prostate diverticula empty into a separate duct that joins the spermiduct at the level of the spermatheca; and the penial canal opens subterminally.In other respects the present description confirms his findings.

DISCUSSION
There is a high degree of similarity between the present species and Plesiophysa hubendicki, as described by Richards & Ferguson (1962).The only appreciable unlikeness is in the ovotestis, not described and represented in a different position from Fig. 11 of the present paper.If a closer observation of that organ reveals its similarity with P. ornata's, there will remain no anatomical support for considering them different species.