Nais communis Piguet, 1906 is a freshwater oligochaete worm that is uncommon in the Great Lakes. It is a naidid worm with dorsal bundles beginning in VI and ventral bundles beginning in II, hair chaetae in the dorsal bundles, and without a proboscis. Worms in the genus Nais all have 1–2 hair and needle chaetae in each dorsal bundle with simple-pointed or bifid needles; the ventrals usually change between V and VI, often quite dramatically. However, Nais communis is known for not having much difference between anterior and posterior ventral chaetae. N. communis has dorsal bundles with 1–2 hair chaetae and 1–2 bifid needles with short equal, parallel teeth that can be seen at 40X. Anterior ventral bundles of II–V have 2–6 chaetae with teeth of equal length. There is not much change in shape at VI and posterior, unlike most other Nais species, except that the placement of the nodulus may be median anteriorly and distal posteriorly. There are usually eyes present. In live specimens, you may notice that there is a gradual widening of the stomach and that this species cannot swim, but these are less helpful for slide-mounted specimens. If mature, there are two or three penial chaetae per bundle. There are no enlarged or giant chaetae. It is possible that N. communis may be part of the N. variabilis complex.
N. communis is identified mainly by dorsal bundles with few hairs and bifid needles starting in VI, ventral chaetae with equal teeth that do not change shape between V and VI like most other species in Nais, and usually having eyes.
This species occurs in all five Great Lakes.
N. communis may be part of the N. variabilis complex as it is often confused with Nais variabilis and there are some specimens with overlapping characteristics that are sometimes simply called N. communis/variabilis. N. variabilis usually has a marked change from anterior to posterior ventral chaetae, anterior chaetae being thin with the upper tooth curved and longer than the bottom tooth, while the posterior chaetae are larger and thicker with the teeth approximately equal but the upper is thin and the lower is thick. However, the chaetae of N. variabilis are variable, so sometimes it is still hard to distinguish. The needle chaetae of N. communis are bifid and the teeth can be seen at 40X, but in N. variabilis the teeth may need to be viewed under 100X to be seen. The nodulus on the anterior chaetae of N. communis is median, while the nodulus on the anterior chaetae of N. variabilis is below the median (closer to proximal end); in both species, the nodulus of the posterior chaetae is distal. The hair chaetae of N. variabilis are usually longer and thicker than N. communis. Lastly, though this may be hard to see, the stomach of N. communis widens gradually, while in N. variabilis the stomach widens abruptly.
N. communis may also be confused with Nais elinguis because both species have bifid needles and do not have much change in the length or width of anterior and posterior ventral chaetae. However, N. elinguis may have 1–3 hairs and needles instead of 1–2, and the needle chaetae have very long parallel teeth, perhaps the longest teeth of the Nais species with bifid needles. The needle chaetae of N. communis are shorter and may appear more divergent when compared with the long, parallel teeth of N. elinguis. The ventral chaetae of N. elinguis have the upper tooth up to twice as long as the lower tooth. When mature, it has 4–5 penial chaetae instead of 2–3 like N. communis. N. elinguis is not usually found in Great Lakes samples, though it may be found in nearshore areas or tributaries.
Some specimens of Dero will key out to N. communis or N. variabilis if they are missing a posterior end since both genuses have 1–2 hairs with 1–2 bifid needles and dorsal bundles starting in V or VI. Specimens belonging to Dero sp. are most likely to Dero digitata, D. obtusa, and D. nivea. D. digitata has needle chaetae with the upper tooth longer than the lower, whereas N. communis or N. variabilis will have even teeth. Another distinguishing factor is the ventral chaetae: D. digitata does experience a difference between anterior and posterior ventrals, and the anteriors are longer and thinner with upper teeth longer than the lower; N. variabilis is quite similar, but the posterior chaetae have a much thicker lower tooth, although there is much variation in the ventral chaetae of this species; N. communis does not have much difference between anterior and posterior chaetae, so the anterior chaetae do not have upper teeth longer than the lower. D. obtusa and D. nivea both have equal teeth on their needle chaetae, but their body size and the length of the anterior ventrals can help distinguish them. If a specimen is missing the posterior end but aligns with other factors for Dero but not a specific species, call it Dero sp.
N. communis is a small freshwater oligochaete.
No, this species does not yet have a barcode reference from the Great Lakes.
Figure 1. N. communis often has eyespots.
Figure 2. These dorsal bundles have 1 hair chaetae and 1 bifid chaetae with two divergent teeth visible at 40X.
Figure 3. There is little difference between anterior and posterior chaetae.
Kathman, R.D., and R.O. Brinkhurst. 1998. Guide to Freshwater Oligochaetes of North America. pp. 88–89, 40, 66–75, 80–89.
Hiltunen, J.K., and D.J. Klemm. 1980. A Guide to the Naididae (Annelida: Clitellata: Oligochaeta) of North America. pp. 22, 35.
