Potamothrix bedoti

  • photomicrograph of part of a freshwater oligochaete worm showing bundles of chaetae and hairs in segments III and IV. There are two or more hairs per bundle with forked chaetae with two tines and maybe some very hard to see intermediate teeth. Scale bar 100 um.

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    Figure 1. Unlike Potamothrix vejdovskyi, P. bedoti appears just like other tubificids with hairs if it is not mature. The anterior dorsal bundles have 3–4 hairs with 3–4 pectinate chaetae with the upper teeth longer than the lower. Posteriorly, the upper teeth are noticeably longer than the lower teeth.

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  • photomicrograph of part of a freshwater oligochaete worm showing bundles of chaetae in segments V and VI. There are five chaetae per bundle, slightly curved with two teeth at the end with the upper tooth as long as or longer than the lower tooth. Scale bar 100 um.

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    Figure 2. There are 3–4 bifid chaetae in the ventral bundles, with the upper teeth slightly longer and thinner than the lower.

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  • photomicrograph of part of a freshwater oligochaete worm showing a bundle of specialized chaetae in segment VII. There are three curled blade-shaped chaetae with two sides that taper to a point. Scale bar 100 um.

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    Figure 3. The spermathecal chaetae may appear in one or many segments between VI and XII, with short blade-shaped tips, although the shape may vary with the degree of maturity. The spermathecal chaetae are smaller and less robust than those of P. bavaricus, P. vejdovskyi, and P. moldaviensis, and may be accompanied by regular ventral chaetae.

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  • photomicrograph of part of a freshwater oligochaete worm showing two bundles of specialized chaetae in segment VII and VIII. There are one or two blade-shaped chaetae with two sides that taper to a point sticking out of the body of the worm. Scale bar 100 um.

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    Figure 4. There are two segments with spermathecal chaetae in this specimen.

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  • photomicrograph of part of a freshwater oligochaete worm showing two bundles of specialized chaetae in segment VIII and IX. There are two bifid chaetae and two blade-shaped chaetae with two sides that taper to a point in IX and there is a very wide bifid chaetae in VIII that is a mix between the two types. Scale bar 100 um.

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    Figure 5. There are two segments with spermathecal chaetae in this specimen, as well as a mixture of normal ventral chaetae, spermathecal chaetae, and at least one chaetae that seems to be an imperfect spermathecal that is a bifid spermathecal chaetae.

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Potamothrix bedoti

Taxa description

Potamothrix bedoti (Piguet, 1913) is a freshwater oligochaete worm that is an uncommon oligochaete in the Great Lakes. It is a tubificid worm with dorsal hairs and pectinate chaetae beginning in II and ventral chaetae are bifid. It has spermathecal chaetae on VII, VIII, or on any of VI-XII. The anterior dorsal bundles have 3–4 hairs with 3–4 pectinate chaetae with the upper teeth longer than the lower. Posteriorly, the upper teeth are noticeably longer than the lower teeth. There are 3–4 bifid chaetae in the ventral bundles, with the upper teeth slightly longer and thinner than the lower. The spermathecal chaetae may appear in one or many segments between VI and XII, with short blade-shaped tips, although the shape may vary with the degree of maturity. Penes without penis sheaths are on IX, prostate glands are absent, and spermathecae are in VIII. P. bedoti was once considered a variant form of P. bavaricus. P. bedoti readily fragments and most of its reproduction is thought to be asexual (Timm 2020).

Distinguishing features

P. bedoti is identified by the having dorsal bundles with hair and pectinate chaetae with the upper teeth longer than the lower, but especially because there are blade-shaped spermathecal chaetae on VII-VIII or any or all of VI–XII. There are non-papillate body walls and no penis sheaths.

Habitat

Often found in the profundal area of lakes, preferring silty muck substrates.

Lake occurrence

Lakes Erie, Huron, and Michigan.

Similar species

Without the presence of reproductive features (in this case, spermathecal chaetae), many tubificid worm species can only be identified as “immature tubificid with or without hair.” P. bedoti is most likely to be confused with other Potamothrix species, but none of them will have spermathecal chaetae that appear on any or all of VI–XII, they are mostly on X or maybe XI. The closest species would be Potamothrix bavaricus, which also has pectinate chaetae with hairs, but the teeth are equal lengths and may become bifid posteriorly with missing hair chaetae. The biggest difference, however, is that P. bavaricus has broad, spear-shaped spermathecal chaetae in X only. The other possibility is Potamothrix hammoniensis which has hairs with pectinate chaetae that become bifid posteriorly and up to 2 long, narrow spermathecal chaetae per bundle on X and sometimes also IX. However, P. hammoniensis has not been confirmed in North America and the few reported specimens were actually Potamothrix vejdovskyi.

Relative size

P. bedoti is a large freshwater oligochaete.

Does it have a barcode reference from the Great Lakes?

No, this species does not yet have a barcode reference from the Great Lakes.

References

Kathman, R.D., and R.O. Brinkhurst. 1998. Guide to Freshwater Oligochaetes of North America. pp. 150–153, 106, 120.

Stimpson, K.S., D.J. Klemm, and J.K. Hiltunen. 1982. A Guide to the Freshwater Tubificidae (Annelida: Clitellata: Oligochaeta) of North America. pp. 24, 26, 48.

Occurrence in scientific literature

Timm, T. 2020. Observations on the life cycles of aquatic Oligochaeta in aquaria. Zoosymposia 17: 102–120.