Sphalloplana (Sphalloplana) mohri Hyman 1938

Sphalloplana (Speophila) mohri Hyman, 1938

Sphalloplana mohri Hyman, 1938:137.

Sphalloplana kutscheri Mitchell, 1968:598.

Sphalloplana sloani Mitchell, 1968:600.

Sphalloplana zeschi Mitchell, 1968:604.

Sphalloplana reddelli Mitchell, 1968:607.

Sphalloplana (Polypharyngea) mohri.—Carpenter, 1971:1284.

TYPE MATERIAL.—Sphalloplana mohri, holotype, whole mount, AMNH 650; paratypes, two specimens (one whole mount and one set of serial sections on 24 slides), AMNH 651. S. kutscheri, holotype, set of serial sections on 35 slides, USNM 38982; two paratypes. S. sloani, holotype, set of serial sections on 36 slides, USNM 38980; three paratypes. S. zeschi, holotype, set of serial sections on 10 slides, USNM 38981; eight paratypes. S. reddelli, holotype, set of serial sections on 7 slides, USNM 38979; four paratypes. The paratypes of Mitchell's species are in the collection of Dr. R. W. Mitchell.

Sphalloplana mohri was first briefly mentioned by Hyman (1938:137) and later (1939:276–280) more fully described. Mitchell (1968) established four additional species on the basis of minor differences in the structure of the reproductive system, which in my opinion do not justify their specific differentiation from S. mohri. The published descriptions offer a sufficiently clear account of the external aspects and the anatomy of the species. The essential characters of the species are the following.

EXTERNAL FEATURES (Figure 16).—Sphalloplana mohri is the largest species of the genus, mature animals attaining a length of 20–30 mm and even 35 mm. Photographs of the species have been published by Mitchell (1974:413, a well-extended specimen, and pp. 415, 420, and 422, all “S. zeschi”) and earlier by Mohr (1948:17, “planarian”), and outline drawings by Mitchell (1968:608). The anterior end is truncate, with a straight or slightly bulging frontal margin, the lateral edges bearing short auricular projections extending laterally and anteriorly. The adhesive organ in the center of the frontal margin may appear retracted or protruded as a pointed conical structure. Behind the auricles, the head narrows to some extent, then widens again gradually to reach its maximum width. The anterior border of the intestinal area appears to have a V-shaped outline as seen in Carpenter's (1970) Figure 13. An important character of the species is its polypharyngy. Hyman (1939:276) gives the number of pharynges as being about 50, Mitchell (1968) as 40 for all his species. The elongated pharyngeal pouch, measuring about one-fourth to one-third the body length, begins at a level anterior to the middle of the body.

ANATOMY.—The adhesive organ, when retracted, forms a rather deep invagination with irregular, folded walls, as indicated by Mitchell (1968:612); when protruded, it appears as a broad, pointed, conical projection. Hyman (1939:276) states that the epidermis along the lateral margins of the body does not show the large rhabdites usually seen in the species of Sphalloplana. The marginal epithelium is thicker than elsewhere, however, and tapers gradually toward the dorsal and ventral surfaces.

The testes, in moderate number, are arranged in a pair of longitudinal rows beginning some distance behind the head and ending at the level of the more anterior pharynges. In Mitchell's type slides they are seen in a predominantly dorsal position. The copulatory apparatus (Figure 62) in the various specimens studied by Mitchell appears to be subject to small variations, probably due to various states of muscular contraction. The penis has a small, not very muscular bulb and a larger, cylindrical or conical papilla with rounded or more or less pointed tip. The vasa deferentia (vd) enter the anterior side of the bulb, traverse it, and unite within the papilla to a straight canal, the ejaculatory duct (de), which opens at the tip of the papilla. There is no distinct seminal vesicle developed, although the ejaculatory duct may show some local widening such as that seen in Hyman's Figure 4, which she interprets as a seminal vesicle. The common oviduct (odc) opens into the posterior part of the male atrium from the dorsal side. The bursal duct (bd) proceeds from the copulatory bursa (b) posteriorly above the penis as a straight, narrow canal, then bends ventrally at the level of the gonopore (gp), widens somewhat, and acquires a thick muscular coat. This terminal section of the duct (v) may be considered to be a vagina.

DISTRIBUTION AND ECOLOGY.—Sphalloplana mohri has been reported from several caves in Texas. Ezell's Cave (type-locality) in Hays County, collected by Charles E. Mohr and Kenneth Dearolf, 19 June 1938 (Hyman, 1939:280), also recorded by Mitchell (1968:609). Mitchell's species are from four other caves of the Edwards Plateau of Texas (Mitchell, 1968: S. kutscheri, Spanish Wells Cave, Travis County, collected by Mitchell, 9 June 1967; S. sloani, Harrell's Cave, San Saba County, collected by Mitchell, 14 October 1967; S. zeschi, Zesch Ranch Cave, Mason County, collected by Mitchell, 10 June 1968 and other dates; and S. reddelli, Cascade Caverns, Kendall County, collected by James Reddell, 8 April 1966). Eigenmann (1900:229 and 1902:84–85) reported the finding of an unidentified flatworm in the outflow of an artesian well in San Marcos, Hays County. Dr. Glenn Longley brought me a preserved, slightly damaged specimen of a polypharyngeal Sphalloplana from this well, collected 28 October 1974 by Joe Kolb. The specimen was not fully mature sexually, but agreed in all recognizable characters with S. mohri.

A few data on the habitat of S. mohri have been presented by Hyman (1939:280), whose material was from a shallow pool in Ezell's Cave with a water temperature of 71°F–72°F [about 22°C]. Mitchell (1974) gives more data on the ecology of his S. zeschi in Zesch Ranch Cave. The worms occur there in an intermittent pool with a temperature of 21°C–21.5°C, together with the amphipod, Stygonectes russelli Holsinger, and an ostracod, Candona sp. Their natural food appears to consist of injured or moribund amphipods and of any other arthropods (cave crickets, flies, etc.) that may have fallen into the water.

LABORATORY STUDIES.—Mitchell (1974) performed some very interesting experiments on S. zeschi. He analyzed the types and speed of movement, the righting time from an inverted position, attraction to food and mode of feeding, negative rheotaxis, responses to light, and temperature tolerance and preference.

TAXONOMIC POSITION.—The well-developed adhesive organ places S. mohri in the subgenus Speophila. It shows, however, certain characters that differ from the general features of this subgenus. The absence of distinct zone of tall epithelial cells on the lateral margins of the body appears to be unique within the genus Sphalloplana. The polypharyngy, also a unique character, should not be given great systematic value, as it occurs in other genera (Phagocata, Crenobia) as a specific or even subspecific feature. It is, however, a good distinguishing character of the species. The small differences in the anatomy of the forms described by Mitchell (1968) are, in the writer's judgment, well within the framework of the expected variations caused by contractions and distortions of muscular organs in the process of fixation, particularly when different methods of killing (nitric acid, formalin) are employed.