Sphalloplana (Sphalloplana) consimilis Kenk 1977

Sphalloplana (Sphalloplana) consimilis

TYPE MATERIALS.—Holotype, set of sagittal sections on 7 slides, USNM 53407. Paratypes, eight sets of sagittal sections on 46 slides, USNM 53408–53415.

EXTERNAL FEATURES (Figures 5, 22).—Fully grown specimens are up to 14 mm long and 2 mm wide. The head has a bulging frontal margin and rather well-developed rounded auricles projecting anteriorly and laterally. In the center of the frontal margin, a moderately developed adhesive organ is discernible, which may be protruded as a conical, pointed projection. Behind the auricles, the body narrows somewhat, forming a necklike constriction, then widens again. In the greater part of the body, the lateral margins run parallel, tapering again in the postpharyngeal region to meet at the more or less pointed posterior end. The rather long pharynx, measuring about one-sixth of the body length, is inserted behind the middle of the body. The copulatory complex occupies the anterior half of the postpharyngeal region. The color of the worm is purely white in most specimens. Animals from Buis Saltpeter Cave, however, showed a light pinkish hue in the neck region and in the area of the copulatory organs. The anterior margin of the intestinal area does not form the V-shaped lateral extensions seen in some species that have a more pronounced adhesive organ.

ANATOMY.—The thickened marginal epithelium is typically developed. The adhesive organ (Figure 34) appears in the slides as a shallow subterminal pit, part of which is invaginated, but not as deeply as in representatives of the subgenus Speophila. Both the pit and the invagination receive numerous eosinophilic gland ducts and are connected with muscle fibers that presumably act as retractors.

In the reproductive system, the ovaries are located behind or below the second to fourth lateral branches of the anterior intestinal trunk. The rather numerous testes (Figure 41), of moderate size, are in a strictly dorsal position. They occupy, on either side of the midline, a longitudinal zone beginning at a considerable distance posterior to the ovaries (behind the sixth to eighth lateral intestinal branches) and extending to the level of the pharynx root. The thin anterior vasa deferentia run parallel to the ventral nerve cords, somewhat removed from them, medially to the oviducts.

The copulatory apparatus (Figure 51) was analyzed in sagittal sections of 10 specimens. The genital atrium is divided into an anterior male atrium (am) containing the penis and a posterior common atrium that receives the outlet of the copulatory bursa. Below the infranucleate atrial epithelium are the usual two muscle layers, a circular one and a longitudinal one. The penis has a weakly developed, not very muscular bulb and a short, rounded or plug-shaped papilla, which is covered by a flattened to cuboidal, infranucleate epithelium with an underlying very feeble muscle layer. Faintly eosinophilic gland ducts (gl) enter the penis bulb from the surrounding mesenchyme and penetrate the penial tissues to open on the surface of the penis papilla. The two vasa deferentia (vd), after widening in the pharyngeal region to form the usual spermiductal vesicles, approach the ventral side of the penis bulb, proceed medially, and open into the anterior end of the tubular penis lumen. There is no seminal vesicle developed. The lumen consists of a short canal (de), surrounded by a muscle coat, which begins in the anteroventral portion of the penis bulb, proceeds first posterodorsally, then arches posteroventrally and opens on the ventral side of the penis papilla very near its base. It apparently acts as an ejaculatory duct.

The common oviduct (odc), provided with numerous eosinophilic shell glands, opens into the atrium from the dorsal side near the transition between the two atria, rather far removed from the gonopore (gp). The copulatory bursa (b) is round or ovoid. Its outlet, the bursal duct (bd), first runs posteriorly, above the penis, as a rather narrow canal, then bends ventrally and sometimes expands into a very wide compartment, the vagina (v). The musculature surrounding the duct consists of intermingled circular and longitudinal fibers.

Remarkable is the wide occurrence of infranucleate epithelia in the copulatory complex of the species at full sexual maturity. The covering of the penis papilla and the linings of the atria, the bursal canal (including the vagina), and the common oviduct are all infranucleate.

DISTRIBUTION AND ECOLOGY.—Sphalloplana consimilis has been collected in several caves in western Virginia and northeastern Tennessee.

TENNESSEE. CLAIBORNE COUNTY: (1) Buis Saltpeter Cave, northeast of Tazewell, 3 specimens collected 19 August 1972 by J. R. Holsinger and D. C. Culver and sent to me alive.

VIRGINIA. LEE COUNTY: (1) Bowling Cave, east of Ben Hur, 1 specimen collected 28 July 1967 by J. R. Holsinger. (2) Cope Cave, south-southeast of Jonesville, 6 specimens collected 23 August 1969 by J. R. Holsinger. (3) Gallohan Cave No. 1, type-locality, 8 specimens collected 26 August 1971 by J. R. Holsinger, D. C. Culver, and J. M. Beck and sent to me alive; they were associated with the isopods, Asellus recurvatus and Lirceus usdagalun, the amphipod, Crangonyx antennatus, and the snail, Fontigens sp. (see Holsinger and Bowman, 1973:267). (4) Gregory's Cave, east-southeast of Rose Hill, several specimens collected 27 October 1967 by J. R. Holsinger. (5) McClure's Cave, west of Jonesville, 9 August 1973, 5 specimens; 31 July 1974, about 50 specimens collected by J. R. Holsinger and D. C. Culver from a huge population of perhaps 300 worms, sent to me alive.

TAXONOMIC POSITION.—By the anatomy of the moderately developed adhesive organ, S. consimilis forms a transition between the subgenera Sphalloplana and Speophila. The most outstanding characteristic of the species is the configuration of the penis, specifically the lack of a seminal vesicle and the opening of the ejaculatory duct on the ventral side near the base of the short, pluglike papilla. A similar feature is seen in S. virginiana, which species, however, has the testes positioned ventrally, while in S. consimilis they are located on the dorsal side. The species name, consimilis (Latin, similar), refers to the great similarity of the copulatory complex with that of S. virginiana.