Comprehensive Description

provided by Smithsonian Contributions to Zoology
Polycelis (Seidlia) sierrensis

HOLOTYPE.–Deep Creek, Placer County, California; series of sagittal sections, USNM 46053.

EXTERNAL FEATURES.–Mature animals are up to 22 mm long and about 2 mm wide. Head truncate, with slightly bulging frontal margin and a pair of bluntly pointed auricles extending from the lateral edges anterolaterally (Figure 7). After a slight narrowing or neck behind the auricles, the body margins first diverge, then run parallel throughout the greater part of the body length. Behind the copulatory apparatus the body narrows again and forms a pointed to rounded posterior end.

The dorsal side is dark brown; the areas above the pharynx and the copulatory complex are somewhat lighter. Ventral side grayish brown, with white spots indicating the sites of the mouth and the gonopore. The numerous eyes (Figure 6C) form a band along the margin of the head and the anterior part of the prepharyngeal region. This band may be interrupted at the base of the auricles. On the head it is more than one row wide, but it narrows posteriorly to a single row. The number of the eyes varies within wide limits. There are fewer eyes in smaller (younger?) individuals than in larger ones. In adult specimens 36 to 108 eyes were counted on either side of the head, not necessarily symmetrically arranged.

The pharynx is rather long, about one-fourth the length of the body. Its insertion or root is at, or somewhat anterior to, the middle of the body. The copulatory complex occupies two-thirds of the postpharyngeal region.

As seen from this description, P. sierrensis cannot be distinguished from P. coronata in life with certainty. In P. sierrensis, the band of eyes may be narrower and slightly more marginal than in P. coronata, but this is not the case in all individuals.

REPRODUCTIVE SYSTEM.–The testes are ventral and are arranged in a pair of rather short bands in the posterior half of the prepharyngeal region, situated on either side of the anterior intestinal ramus and extending laterally as far as the ventral nerve cords. The ovaries are located at the level of the first or second lateral intestinal branches, somewhat anterior to the testicular bands.

The copulatory complex (Figure 8) shows the genital atrium divided into a small posterior common atrium (ac) and a larger anterior male atrium (am), the two subdivisions communicating by means of a narrow canal which, in fully mature animals, runs in the axis of a conical papilla (pa) projecting into the male atrium; this atrial papilla or diaphragm is developed only at full maturity. The common atrium connects with the genital aperture (gp), the outlet (bd) of the copulatory bursa (b), and the common oviduct (odc). The male atrium, which is lined with a cuboidal epithelium, is surrounded by a very thick, massive muscular layer (ma) consisting chiefly of circular fibers interspersed with less numerous longitudinal fibers. The penis has a rounded bulb and a conical papilla (pp). The bulb contains a large cavity (pl) with villus-like processes projecting from the wall. Posteriorly, toward the penis papilla, the cavity narrows and its wall becomes smooth, forming what may be compared to an ejaculatory duct. The cavity opens at the tip of the penis papilla.

The two vasa deferentia, which at the sides of the pharynx have enlarged to spermiductal vesicles, turn upward and medially at the level of the penis bulb, approach the bulb, enter it from the sides, and open separately into the bulbar lumen. The lumen also receives many ducts originating from unicellular glands located in the parenchyma surrounding the penis. The two oviducts unite in the space above the common genital atrium, forming a short common oviduct (odc) which empties into the common atrium from the dorsal side. The end parts of the paired oviducts and the common oviduct receive many outlets of eosinophilic glands.

The copulatory bursa (b) is a large, lobate sac without prominent lateral extensions. Its duct (bd) runs posteriorly, normally on the right side of the midline (only exceptionally above the penis). The secretory epithelium lining the bursa extends some distance into the anterior part of the bursal duct.

ECOLOGY AND DISTRIBUTION.–Polycelis sierrensis was collected in cold springs and streams in the region of the Sierra Nevada of California and Nevada. The few observations on the physicochemical conditions of its habitats do not permit definitive conclusions concerning the ecological requirements of the species. The temperature range of the water was between 6.2° and 16.5°C, with an average of 9.2°C (12 measurements); the pH between 6.1 and 7.7, average 7.0 (11 measurements); and the oxygen content between 7 and 10 parts per million, average 9 ppm (4 measurements). It must be pointed out, however, that these observations were made in the warmer seasons of the year, from late May to September, and that no data are available on the seasonal fluctuations of these parameters. Other factors which may influence the occurrence of the species, such as the chemical composition of the water, the available food supply, etc., have not been studied. Sexually mature individuals were taken in the following localities:

CALIFORNIA. MARIPOSA COUNTY: Fern Spring, in Yosemite National Park, on road connecting State Roads 140 and 41. Limnocrene with considerable water flow and several seepage springs above it; 3 July 1967, water temperature 6.4° and 6.8°C, pH 6.1 and 6.2; several specimens under stones, one of them mature, one with regenerating head. 5 July 1968, temperature 7.3°C, 17 specimens of various sizes, 2 mature. NEVADA COUNTY: Spring near Sagehen Creek Biological Station, tributary of Sagehen Creek, furnishing water to the station. Situated about 2 miles west of State Road 89, north of Truckee; 23 September 1967, water clear, fast, temperature 6.3°C, pH 7.5, under stones 3 specimens; 10 July 1968, 6.5°C, pH 7.5, oxygen 10 ppm, many specimens under stones, some mature; 28 and 29 May 1970, temperature 6.3°C, pH 7.5, oxygen 9 ppm, about 50 Polycelis under stones and on bait (beef liver) exposed over night, some mature. Besides this species, less numerous Phagocata crenophila Carpenter. PLACER COUNTY: (1) McKinney Creek near its mouth on the west shore of Lake Tahoe, close to the El Dorado County line; 21 June 1967, clear, fast water, 9.0°C, pH 7.1, about 10 specimens under stones, 2 mature. (2) Tahoe City, overflow of spring furnishing water to the local California Fish and Game facility, on State Road 28, 1.7 road miles northeast of junction with State Road 89; 23 September 1967, water clear, fast, temperature 6.7°C, pH 6.8, 6 immature Polycelis under stones; 10 July 1968, 6.2°C, pH 6.6, oxygen 10 ppm, several Polycelis under stones, 2 of them mature; 28 and 29 May 1970, 10.0°C, pH 7.0, oxygen 7 ppm, many mature and immature specimens under stones and on liver bait. Besides Polycelis, Phagocata crenophila occurs here. (3) Deep Creek, at crossing of State Road 89 south of Truckee (type-locality of Polycelis sierrensis); 23 September 1967, water clear, fast current, temperature 10.6°C, pH 7.7, 4 immature post-fission specimens under stones; 10 July 1968, 3 specimens, 2 of them mature.

NEVADA. WASHOE COUNTY: Marlette Creek, along State Road 28, about ½ mile north of Ormsby County line; 11 July 1968, water clear, fast, 16.5°C, pH 7.4, 2 specimens under stones, 1 mature.

LIFE CYCLE.–The few sexually mature specimens collected from May to September allow no conclusions regarding the breeding season of the species. Generally they were taken together with more numerous asexual specimens some of which in individual cases showed signs of active fission. No egg capsules were seen in the field. No attempt was made to culture the species in the laboratory. Presumably it could be maintained in cold-water cultures, with liver as food, since it has been successfully attracted by beef liver used as bait.

TAXONOMIC POSITION.–P. sierrensis is rather closely related to a Japanese species, P. auriculata Ijima and Kaburaki (1916). Through the courtesy of Dr. Masaharu Kawakatsu of Fuji Women’s College in Sapporo, Japan, who kindly sent me several living specimens of P. auriculata from Hidaka, Hokkaido, I was able to compare the two species in greater detail. Externally P. auriculata is similar to P. sierrensis by its general shape, size, and pigmentation. There is a difference in the arrangement of the eyes which in P. auriculata form a wider, horseshoe-shaped band which does not reach as far backward as in P. sierrensis (Figure 6C,D). In the copulatory apparatus the differences mainly concern the atrial papilla or diaphragm and the shape of the copulatory bursa (Figures 8 and 9). In P. auriculata the atrial papilla (pa) is much larger and more pointed than in P. sierrensis. The copulatory bursa (b) is smaller and forms a pair of anterolateral extension or horns (see Ijima and Kaburaki, 1916:168; Kaburaki, 1922:40), while in P. sierrensis it is a large, lobate sac. Another peculiarity which I noticed in the three specimens of P. auriculata studied was the formation of an intestinal anastomosis (i) below the copulatory complex, observed also by Okugawa (1938:177), which was absent in P. sierrensis. This anastomosis or transversal commissure is lined with the normal intestinal epithelium and lacks a special muscular coat such as is seen in a related species from Japan and Kamchatka, P. schmidti [=Rjabuschinskya schmidti Zabusov (1916:276); Polycelis ijimai Kaburaki (1922:45)]. This commissure may not be a specific characteristic of P. auriculata, since anastomoses between the two posterior intestinal rami are frequently observed in other species as well and are subject to great individual variation. Kaburaki (1922:40, fig. 12), in his figure of the digestive system of P. auriculata indicates such an anastomosis behind the copulatory apparatus. Another species related to P. sierrensis is P. sabussowi (Seidl) from Turkestan which has an almost identical structure of the copulatory organs but lacks the atrial papilla (see Kenk, 1936).

Polycelis species

Because of the scarcity of sexually mature specimens in the collections of Polycelis and the lack of external characters which might distinguish the individual taxa, many of the lots taken in the field could not be identified to species. Unfortunately this is true for the great majority of the locality records of the genus in North America. In some cases the presence of identifiable specimens in the vicinity of a given locality may give a hint as to the taxonomic identity of the immature forms but would not preclude the risk of misidentification. I am, therefore, listing here all distributional records known to me which need further study.

ALASKA. (1) to (7) Six streams and one lake on road from Palmer to Willow (Kenk, 1953:173). (8) to (13) Six streams on Glen Highway, between Anchorage and Glenallen (Kenk, 1953:173). (14) and (15) Two streams on road from Anchorage to Potter (Kenk, 1953:173). (16) to (25) Nine Streams and one lake on Richardson Highway, between Glenallen and Valdez (Kenk, 1953:173). (26) Stream 9 miles north of Seward (Holmquist, 1967:463). (27) Near Johnson Pass, 66 miles from Anchorage (Holmquist, 1967:463).

CALIFORNIA. EL DORADO COUNTY: Tributary of South Fork of American River, crossing U. S. Highway 50, 5.9 road miles east of Pacific House; 23 June 1967, water clear, fast, 10.1 °C, pH 7.3, many specimens under stones. MARIPOSA COUNTY: (1) Tributary of Yosemite Creek, on Yosemite Falls Trail, Yosemite National Park; 3 July 1967, 5 specimens. (2) Wildcat Creek, Yosemite National Park, crossing Big Oak Flat Road, 2.3 miles west of junction with State Road 140; 3 July 1967, water clear, fast, 14.6°C, pH 7.2, 3 specimens under stones. MONO COUNTY: (1) Convict Creek in Long Valley, at an altitude of 7200 feet (Kennedy, 1967:8). (2) Stream on Tioga Road (State Road 120) at timberline near Tioga Pass; 18 October 1970, 7 specimens collected by Dr. Vida C. Kenk. NEVADA COUNTY: Sagehen Creek at Sagehen Creek Biological Station, 1.7 road miles west of State Road 89, north of Truckee; 9 July 1968, water clear, fast, temperature 18.1 °C, pH over 7.6, oxygen 7 ppm, many specimens, some with signs of fission; 29 May 1970, 13.0°C, pH 7.6, many small specimens. SANTA CLARA COUNTY: Springs of Black Creek, on east slope of Black Mountain, southwest of Los Gatos; bottom silt with stones; 3 June 1967, water temperature 11.0° and 11.5°C, pH 6.7, 12 immature specimens under stones; 25 June 1967, 6 specimens. SANTA CRUZ COUNTY: (1) Tributary of San Lorenzo River, crossing State Road 9 at Brookdale; 4 June 1967, water clear, fast, 11.2°C, pH 8.0, one specimen under a stone. (2) Fall Creek, about ½ mile west of Felton, San Lorenzo River Valley; 4 June 1967, water clear, fast, 11.6°C, pH 8.3, one specimen under a stone. (3) Fall Creek, above fork leading to old mine; 4 July 1968, water clear, fast current, temperature 13.4°C, pH 7.9, 3 worms under stones. (4) Small spring on right bank of tributary of Fall Creek which leads to old mine; 4 July 1968, water clear, moderate current, temperature 12.3°C, pH 7.4, 2 immature Polycelis under stone and fallen leaf. (5) Tributary of Fall Creek, at site of old mine; 4 July 1968, water clear, fast, 12.3°C, 3 specimens under stones. TULARE COUNTY: (1) East Fork of Redwood Creek, in Sequoia National Forest, crossing State Road 198, 2.2 road miles east of Bearskin Meadow Road; 27 June 1967, water clear, fast, 16.1°C, pH 6.9, 4 immature specimens under stones. (2) Stream crossing State Road 198, 0.9 mile south of Camp Kaweah in Sequioa National Park; 28 June 1967, water clear, fast, 12.2°C, pH 7.2, 4 Polycelis under stones. (3) Tributary of Kaweah Creek, Sequoia National Park, crossing State Road 198, 2 miles west of Lodgepole; 28 June 1967, water clear, fast, 9.9°C, pH 6.0, 4 asexual worms under stones. (4) Tributary of Halstead Creek, crossing State Road 198, 3.7 miles west of Lodgepole, Sequoia National Park; 28 June 1967, water clear, fast, 12.9°C, pH 7.1, one immature specimen under stone. TUOLUMNE COUNTY: (1) Stream crossing Tuolumne Grove Road in Yosemite National Park, 2.3 road miles west of junction with Big Oak Flat Road; 3 July 1967, water clear, fast, 11.1°C, pH 6.2, 4 specimens on fallen branch. (2) Small seepage spring on right bank of stream crossing Tioga Road (State Road 120), 5.6 road miles west of junction with Big Oak Flat Road; 3 July 1967, water 8.4°C, pH 6.0, 2 immature specimens.

COLORADO (see Kenk, 1952:196). BOULDER COUNTY: (1) to (4) Four streams in the St. Vrain Creek Basin, crossing State Road 7. GRAND COUNTY: (1) Onahu Creek, crossing U. S. Highway 34. (2) Tonahutu Creek, above opening into Grand Lake. LARIMER COUNTY: (1) Thompson River east of Estes Park. (2) Fall River at Estes Park. (3) Roaring River (tributary of Fall River).

MONTANA. GALLATIN COUNTY: (1) Small spring on campus of Montana State University, Bozeman; 1 September 1967, water clear, moderate current, 11.7°C, pH 7.4, many immature specimens under stones; February and April 1969, 43 specimens collected and sent by Dr. C. J. D. Brown, none mature. (2) Trout Brook, tributary of East Gallatin River, north-northwest of Bozeman; 2 September 1967, water clear, fast current, 9.6°C, pH 7.8, 6 animals under stones. (3) Spring north of Belgrade, tributary of Thompson Creek, outlet crossing county road 4.3 miles north of junction of U. S. Highway 10 and Montana Secondary Road 347; 4 September 1967, 2 immature Polycelis; 4 June 1970, 14.0°C, 3 Polycelis under stones; Dendrocoelopsis vaginata Hyman also occurs here. LAKE COUNTY: East shore of Flathead Lake, below mouth of a creek off State Road 35, 12 road miles north of junction with U. S. Highway 93; 3 September 1967, one specimen under a stone. MISSOULA COUNTY: Spring and creek, tributary of Rattlesnake Creek, 1 mile from Clark Fork River; 21 May 1968, water slightly muddy, 10°C, 4 immature Polycelis collected by F. P. Crowley, together with Dendrocoelopsis vaginata Hyman. RAVALLI COUNTY: Skalkaho Pass, east of Hamilton, collected by Miss Betty Locker (see Kenk, 1952:196). YELLOWSTONE NATIONAL PARK (Montana sector): Warm Creek, crossing road from Northeast Entrance to Tower Falls Junction, 1.2 miles west of entrance gate; 23 June 1963, water clear, fast, 7.6°C, 4 Polycelis under stones, some with regenerating tails.

NEW MEXICO. BERNALILLO COUNTY: Stream in Cienega Canyon, on east slope of Sandia Mountains, in Cibola National Forest; 16 July 1968, water clear, fast, 12.6°C, pH 8.6, very numerous Polycelis of various sizes, some with indications of preceding fission, none fully mature.

OREGON. CLACKAMAS COUNTY: Spring in Willamette Park, Willamette (12 miles south of Portland); 12 September 1967, water clear, moderate current, 12.1 °C, pH 6.2, many specimens, all asexual, some with signs of fission. KLAMATH COUNTY: (1) Goodbye Creek, Crater Lake National Park, above bridge which leads from the Park Service headquarters to State Road 62; 13 September 1967, water clear, fast, 5 immature specimens under stones. (2) Anne Spring, at south entrance of Crater Lake National Park; 13 September 1967, water clear, 3.1°C, pH 7.0, 11 specimens under stones, some with regenerating tail ends. MULTNOMAH COUNTY: Woodbury Spring, in Crystal Springs area of Eastmoreland district of Portland; 12 September 1967, water clear, 11.2°C, pH 6.3, on liver bait many Polycelis, all immature (besides this species, also Phagocata oregonensis Hyman and Dendrocoelopsis vaginata Hyman). The occurrence of Polycelis in this area is also mentioned by Hyman (1963:2) and Kenk (1970:31).

SOUTH DAKOTA. Brook near the State Game Lodge in the southern part of the Black Hills (Hyman, 1931:124).

UTAH. BEAVER COUNTY: Springs and streams in Puffer Lake area (Beck, 1954:82). CACHE COUNTY. Rick’s Spring in Logan Canyon, on U.S. Highway 89, 16.6 road miles east of Utah State University in Logan; 27 September 1967, water clean, fast, cold, many specimens under stones, some of them mature but not studied (see also Beck, 1954:82; Braithwaite. 1962:24). Phagocata crenophila Carpenter occurs in the same locality. Springs and streams in Dagget, Emery, San Juan, Sanpete, Tooele, Utah, Wasatch, and Wayne counties (Beck, 1954:82; Braithwaite, 1962:24).

WASHINGTON. Streams in Mt. Rainier National Park, Lewis and Pierce counties (USNM 36070 through 36078).

WISCONSIN. DANE COUNTY: Springs near Lake Mendota (Muttkowski, 1918:389, as “Polycelis nigra”).

WYOMING. TETON COUNTY: (1) Stream crossing Jackson Hole highway (U.S. Highway 26), 0.5 mile south of Spread Creek bridge, Grand Teton National Park; 24 June 1963, water clear, 11.6°C, Polycelis in fission under stones. (2) Outflow of fish tanks of Jackson National Fish Hatchery, off U.S. Highway 89, 3½ road miles north of Jackson; 29 September 1967, moderate current, water clear, cold, one Polycelis under a stone. YELLOWSTONE NATIONAL PARK: Twenty-two springs and streams in various parts of the Park; 17-25 June 1963, 7-8 September 1967, and 6 June 1970, water temperature 5.4°-17.3°C, (average 10.3°, 18 measurements), pH 7.7-8.6 (average 8.2, 4 measurements), worms frequently showing signs of asexual reproduction. Muttkowski (1929:183) reported “Polycelis nigra” from various streams in the Park. Specimens from Lava Creek were also collected and sent to me by Jack L. Dean.

CANADA. ALBERTA: Snaring River, Jasper National Park (Ball and Fernando, 1968:213).

The American species and subspecies of Polycelis are probably allopatric in distribution, with some possible sympatry in marginal areas. If this is the case, individual unidentified populations may be assigned, with some confidence, to known forms occuring in the same geographic area. Thus, all records from Alaska, northern Wyoming, and Alberta may refer to P. coronata borealis, populations of Montana, New Mexico, and Utah to P.c. coronata, and those of Colorado and South Dakota to P.c. brevipenis. It is possible that all Polycelis from California are P. sierrensis. These questions will have to be settled by additional collecting, preferably during the height of the breeding season (in winter?).


The genus Polycelis is represented in North America by two species belonging to two subgenera, P. (Polycelis) coronata (Girard) and P. (Seidlia) sierrensis, new species, inhabiting the western half of the continent. P. coronata occurs as three subspecies, P.c. coronata, P.c. borealis, and P.c. brevipenis, differing in the detailed structure of the copulatory apparatus. The North American forms cannot be distinguished by external characters alone, nor can they be identified in immature stages.
bibliographic citation
Kenk, Roman. 1973. "Freshwater triclads (Turbellaria) of North America, V: the genus Polycelis." Smithsonian Contributions to Zoology. 1-15. https://doi.org/10.5479/si.00810282.135