Phagocata undulata (Stankovic 1960)

Phagocata undulata (Stankovi)

Fonticola undulata Stankovi, 1960:178.

Phagocata (? = Fonticola) undulata.—Dahm, 1964:487.

Phagocata (Fonticola) undulata.—Gourbault, 1972:33.

Phagocata undulata.—Kenk, 1974:43.

MATERIAL DEPOSITED.—Sagittal serial sections of 3 specimens on 9 slides, USNM 55309-55311.

Phagocata undulata has been known only from a figure by Stankovi (1960:177, fig. 68b2).

EXTERNAL FEATURES (Figure 23).—Mature animals attain a length of 8 mm and a width of 2 mm. The species is characterized by a strikingly beautiful shape that is unique not only among the representatives of the genus Phagocata, but among the freshwater triclads in general. The lateral margins of the body are thrown into almost regular, wave-like curves and folds that give them a peculiar scalloped appearance. The number of folds on either side is from six to eight, in nearly symmetrical arrangement. The inner margins of the folds extend over the dorsal surface of the body. Except on the frontal outline of the head and the tip of the posterior end, the margin has a row of short conical papillae. The curves and folds are constant features and are distinct in resting as well as gliding animals. They should not be confused with the transitory wavy ruffles that appear in many planarians, particularly in dendrocoelids, when the body is contracted during “crawling” movement or at rest. The frontal margin of the head is more or less rounded or forms a blunt angle at the anterior tip. The body is widest at about the region of the pharynx. The posterior end is usually pointed during locomotion. The animal is unpigmented, white, and rather transparent. The two eyes are situated very close together at a distance of about one-sixth the width of the head, and removed from the frontal margin. The pharynx lies approximately at the middle of the body or somewhat behind it. The intestine is clearly visible in the living animal because of the transparency of the body. The anterior intestinal ramus ends at the level of the eyes and bears on each side four to five lateral branches, which themselves are ramified. Each posterior ramus has many small lateral branches and several short medial branches. The animal moves exclusively by “gliding,” never by “crawling.”

ANATOMY.—The usual smooth, ciliated epithelium is found only on the ventral surface of the body, covering the area that is in contact with the substrate (Figure 28B). The entire dorsal surface and the folds and papillae of the marginal region are covered with a modified epithelium consisting of conical or hemispherical cells lacking cilia (Figure 28A). Each cell contains a large number of small rhabdites surrounding the nucleus. Another type of epithelium occurs along the frontal margin of the head, forming a narrow strip to either side of the midline, immediately above the submarginal zone of adhesive cells. This epithelium is ciliated, infranucleate, and contains very few small rhabdites. Apparently the two strips represent the auricular sense organs.

In the reproductive system, the numerous testes lie predominantly close to the ventral side of the body. Only few are situated more dorsally, particularly in sections where the testes are very crowded. The testicular zone begins immediately behind the ovaries and extends posteriorly almost to the tail end.

The copulatory organs (Figure 34) correspond closely to the scheme characteristic of the Balkanic representatives of the genus Phagocata. The genital pore (gp) leads into a relatively small common atrium (ac) that connects anteriorly with the male atrium (am), the two chambers not being marked off distinctly. The penis consists of a rather small bulb and a conical papilla. The musculature of the bulb is weak, developed mainly near its periphery. The papilla, on the other hand, possesses powerful muscles arranged in a thick layer of circular fibers and a thinner one of longitudinal muscles beneath the outer epithelium. The two vasa deferentia (vd) approach the ventral part of the penis bulb, penetrate it in a medial direction, then turn dorsally and open into the moderately wide lumen of the penis. This lumen is divided histologically into three sections, as is the case also in P. ochridana and P. maculata. At the openings of the vasa deferentia, the epithelium of the lumen consists of very tall cells that are directed toward the papilla and form a plug filling the lumen. Posterior to the plug, the ejaculatory duct (de) is lined with a flatter epithelium that is pierced by numerous eosinophilic gland ducts. Great masses of their secretion are found in the tissues surrounding this region, in the parenchyma of the penis bulb, and adjoining parts of the papilla, particularly in the ventral half of the organ. This secretion is apparently used in the formation of the spermatopositor of the spermatophore. The third section of the penial lumen is usually somewhat widened, lined with a taller epithelium, and opens into the atrium at the tip of the penis papilla.

The two oviducts unite dorsally to the male atrium forming the common oviduct (odc) that opens into the atrium. The end parts of the paired oviducts and the upper three-fourths of the common oviduct are equipped with shell glands. The copulatory bursa (b) sometimes contains remnants of spermatophores. The stalk of the bursa (bd) runs somewhat left of the penis, starting from the bursa as a narrow canal, then curving ventrally while gradually becoming wider, and opening into the common genital atrium from the left side. A large number of eosinophilic gland ducts (gl) open in the area surrounding the genital pore.

ECOLOGY AND DISTRIBUTION.—A total of 32 specimens of Phagocata undulata were collected in August 1937 in Ohrid Bay by dredging at depths between 16 and 26 m in the shell zone of the sublittoral. All animals were small, generally about 3 mm long, and immature. They were placed in a culture maintained at a temperature of 10° C and fed beef liver. They grew and developed sexual structures after several months. Several cocoons were laid and many young hatched between January and May 1938, after which the culture was discontinued. No reproduction by fission occurred in the culture. The fact that only immature animals were collected in August may indicate that reproduction in the lake takes place at some other season, possibly in winter or spring.

Two specimens were observed in copula. They rested at the bottom of the culture dish, parallel to each other, both heads pointing in the same direction The anterior parts of their bodies were attached to the substrate, while the posterior parts were twisted in such a way that the ventral surfaces of the two animals were pressed against each other. When the animals were pulled apart, the two penes could be seen protruding from the genital pores.

TAXONOMIC POSITION.—The peculiar differentiation of permanent folds and papillae along the margin of the body is not duplicated in any other species of freshwater planarians so far known. Phagocata papillifera (Ijima and Kaburaki) of Japan has a linear series of 20 to 25 small papillae along the middorsal line. Numerous papillae spread over the dorsal surfaces are known to occur in two species of Lake Baikal in Siberia, Sorocelis leucocephala Zabusov and Planaria papillosa Korotnev, both now placed in the genus Papilloplana (= Thysanoplana Graff, not Plehn). In an earlier paper (Kenk, 1930:148), I expressed my doubts as to the taxonomic value of projections on the body surface (papillae, etc.). Phagocata undulata fully confirms this opinion. The anatomical structure of the species entirely conforms with the scheme observed in the genus Phagocata and, moreover, the species is more closely related to the Balkanic representatives of the genus than to the remaining Phagocata species of the Eastern and Western Hemispheres. In particular, it is the detailed structure of the male copulatory organ that resembles closely that of P. ochridana and related forms. Phagocata undulata is, therefore, despite its striking external habit, a typical member of the genus Phagocata.

Crenobia Kenk