Piguetiella michiganensis

Piguetiella michiganensis Hiltunen, 1967 is a freshwater oligochaete worm that is an uncommon oligochaete in the Great Lakes. It is a naidid worm with dorsal bundles beginning in VI and ventral bundles beginning in II, without hair chaetae in the dorsal bundles, and without a proboscis. This worm strongly resembles P. blanci except that it lacks hair chaetae and is eyeless, and in fact may be a synonym of the latter; the presence of hair chaetae may be influenced by pH or conductivity. From the description of P. blanci: “Dorsal bundles also contain 2–6 sigmoid bifid needles. Ventral bundles contain 5–8 or up to 10 bifid chaetae that resemble the dorsal needles." If mature, simple-pointed or minutely bifid spermathecal chaetae measuring 115 µm are present in V and may replace ventral chaetae.

P. michiganensis is identified mainly by the dorsal chaetae starting in VI that lack hair chaetae and 2–6 bifid needles with divergent teeth that resemble the ventral chaetae. It is eyeless.

Lakes Michigan and Ontario.

P. michiganensis most closely resembles P. blanci. The main difference between these species is that P. michiganensis lacks hair chaetae and is eyeless, although it is possible for some P. blanci to lack hair chaetae. From Kathman and Brinkhurst, it appears that the spermathecal chaetae of P. blanci are simple-pointed but those of P. michiganensis may be minutely bifid.

P. michiganensis could be confused with Uncinais uncinata, which has dorsal bundles usually starting in VI and lacks hair chaetae. There are 2–4 bifid chaetae dorsally and 2–7 chaetae in ventral bundles. All chaetae in U. uncinata have the upper teeth longer and thinner than the lower, which is not the case for P. michiganensis. Ventral chaetae of II may be longer than the rest, or II–IV may be thinner and longer. Older individuals have eyes, while P. michiganensis is eyeless. Penial chaetae have a simple hook, whereas the spermathecal chaetae of P. michiganensis is simple-pointed or minutely bifid.

It is possible that some P. michiganensis have dorsal chaetae beginning in V instead of VI. In that case, it may be confused with Paranais species. Paranais lacks hair chaetae, so P. michiganensis can be distinguished if it has any hair chaetae at all. P. frici, the most likely Paranais species, has fewer chaetae than P. blanci with 2–4 ventral chaetae in II and 1–2 ventral chaetae posteriorly; the upper teeth are much longer than the lower and hook-shaped. P. frici has transverse furrows on the body wall and may have a thin layer of foreign matter. Instead of spermathecal chaetae in V, there are 2–3 bifid strongly curved penial chaetae.

Rarely, C. diastrophus may have dorsal chaetae starting in VI. If that is so, it might key out to Uncinais uncinata or Piguetiella sp. The chaetae are not shaped like Piguettiella sp. so it is more likely to be confused with U. uncinata, but the arrangement of the chaetae in II, the missing chaetae from III-V, and the enlarged pharynx should help point it back towards C. diastrophus.

P. michiganensis is a small freshwater oligochaete. Mature worms are 5mm long.

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

Kathman, R.D., and R.O. Brinkhurst. 1998. Guide to Freshwater Oligochaetes of North America. pp. 52–53, 34, 38, 48–51.

Hiltunen, J.K., and D.J. Klemm. 1980. A Guide to the Naididae (Annelida: Clitellata: Oligochaeta) of North America. pp. 26, 36, 39.