Schmidtea polychroa
(Schmidt, 1861)
Common Name:
A flatworm
Synonyms and Other Names:
D. lugubris, Planaria polychroa, and P. lugubris
Identification:
This uniform to irregularly pigmented brown flatworm exhibits a rounded to somewhat triangular head that narrows slightly at the neck. The two eyes are located close to the anterior end and spaced further apart than in the North American native D. tigrina. Posterior to the eyes there are two unpigmented auricular sensory organs near the lateral margins that barely protrude from the body and are not especially pointed. The single pharynx is completely white. Cocoons are brown, round, and occur on a stock. (Kenk 1972; Pennak 1989; Wienzierl et al. 1998) Average length in a population varies between 4.5 and 10 mm depending on the time of year but maximum size can reach 20 mm (Reynoldson and Davies 1970; Kenk 1972; Boddington and Mettrick 1974).
Size:
can reach 20 mm
Native Range:
D. polychroa is primarily found in western Europe. However, its Palearctic range encompasses all of Europe, northern Asia, and northern Africa within the Mediterranean basin (de Vries 1985; Mills et al. 1993).
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This map only depicts Great Lakes introductions.
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Great Lakes Nonindigenous Occurrences:
D. polychroa occurred for the first time within the Great Lakes basin in Lake Ontario in 1968 (Ball 1969; Mills et al. 1993).
Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Schmidtea polychroa are found here.
Table last updated 5/1/2024
† Populations may not be currently present.
Ecology:
D. polychroa is hermaphroditic. Different lineages of: a) diploid sexual individuals; and b) polyploid, pseudogamous, parthenogenetic individuals exist. In the latter type of lineage, reproduction occurs when unfertilized eggs develop. Sperm is still required to trigger initial egg development, but genetic material from the sperm is not incorporated. Interbreeding between the two different types of lineages sometimes occurs when sperm produced by parthenogens fertilizes sexual individuals. When copulations take place, both individuals involved transfer and receive sperm. Self fertilization does not occur (Beukeboom et al. 1996; Peters et al. 1996; Weinzierl et al. 1998).
D. polychroa is iteroparous, reproducing many times in a lifetime. In the field, each adult in established populations produces around 0–8 young in a breeding season, but with unlimited food and little competition, each adult can produce around 30– 45 young. Populations in Toronto Harbour, Canada remain low over winter; expand rapidly in spring and summer; peak in August; and then decline. The breeding season in this locality is around 10 weeks long (Boddington and Mettrick 1974; Reynoldson 1977; Bladon and Calow 1987). Distribution of D. polychroa in Toronto Harbour, Canada is limited mostly by pollution. In cleaner areas densities can reach up to 2200 individuals per m2. In this harbor D. polychroa feeds predominantly on tubificid oligochaetes and supplements its diet with gastropods, isopods, and amphipods. In some British habitats this flatworm mainly consumes gastropods, supplemented by amphipods, asellids, and sometimes chironomids. Differences in relative contribution of food items between British populations and North American ones are probably related to prey availability and competition with other predators. In British habitats, competition with other triclads and leeches is very common (Reynoldson and Davies 1970; Boddington and Mettrick 1974; Reynoldson and Piearce 1979; Seaby et al. 1996).
D. polychroa typically occurs in littoral zones, especially in rocky regions of productive lakes. In The Netherlands it is only found in waters above pH of 6.0. It rarely occurs in waters of chlorinity above 2‰ and cannot survive permanently in salinities of 3.8‰ and more, although chlorinity up to 6.6‰ can be tolerated for short periods of time. D. polychroa is relatively thermophilic and requires temperatures of 10–23ºC to complete a full life cycle. Its ability to tolerate increased salt concentrations decreases as temperature increases. It requires water temperatures of 10ºC or more for egg case production and does not grow in water temperatures below 5ºC (Reynoldson et al. 1965; Reynoldson and Davies 1970; Boddington and Mettrick 1974; Van der Velde et al. 1986; Seaby et al. 1996).
Means of Introduction:
D. polychroa was very likely introduced in ballast water to North America (Ball 1969; Mills et al. 1993).
Status:
Established where recorded.
Great Lakes Impacts:
Summary of species impacts derived from literature review. Click on an icon to find out more...
There is little or no evidence to suggest Dugesia polychroa has significant environmental impacts in the Great Lakes.
Realized:
Great Lakes native organisms consumed by Dugesia polychroa include tubificids, gastropods, amphipods, and isopods (Boddington and Mettrick 1974). Throughout much of its distribution in North America, D. polychroa feeds primarily on oligochaetes (Boddington and Mettrick 1974), while the native D. tigrina is believed to feed exclusively on gastropods (Reynoldson 1974). However, in Toronto Harbour, Ontario, D. polychroa and D. tigrina are found to coexist; the latter is found at lower densities, suggesting potential intra-specific competition between the triclads (Boddington and Mettrick 1974).
Potential:
In Britain, competition for food resources, specifically gastropods, is observed between D. polychroa and D. tigrina (Reynoldson and Davies 1970).
There is little or no evidence to suggest Dugesia polychroa has significant socio-economic impacts in the Great Lakes.
There is little or no evidence to suggest Dugesia polychroa has significant beneficial effects in the Great Lakes.
Realized:
Planarians have been used in medicinal and scientific research in topics including, but not limited to, genomics (Alvarado and Newark 1999), stem cells (Newark and Alvarado 2000, Reddien and Alvarado 2004), and cancer (Oviedo et al. 2008), as well as for modeling morphogenesis, restoration of pattern and polarity, control of tissue proportions, and tissue homeostasis (Salo et al. 2009).
Management:
Regulations (pertaining to the Great Lakes region)
There are no known regulations for this species.
Note: Check federal, state/provincial, and local regulations for the most up-to-date information.
Control
Biological
There are no known biological control methods for this species.
Physical
There are no known physical control methods for this species.
Chemical
There are no known chemical control methods for this species.
Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.
Remarks:
In the Great Lakes, D. polychroa benefits from changes in substrate due to increased interstitial space and increased biodeposition provided by introduced mussels in the genus Dreissena (Ricciardi et al. 1997).
References
(click for full reference list)
Author:
Kipp, R.M., A.K.Bogdanoff, and A. Fusaro.
Contributing Agencies:
Revision Date:
9/13/2019
Citation for this information:
Kipp, R.M., A.K.Bogdanoff, and A. Fusaro., 2024, Schmidtea polychroa (Schmidt, 1861): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/GreatLakes/FactSheet.aspx?Species_ID=2359, Revision Date: 9/13/2019, Access Date: 5/1/2024
This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.