Aulodrilus americanus
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Figure 1. The anterior end of Aulodrilus americanus has simple-pointed or minutely bifid chaetae in bundles of up to 10.
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Figure 2. The anterior chaetae are simple-pointed or minutely bifid and there are coelomocytes all over the body, unlike other members of Aulodrilus sp.
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Figure 4. The body is often encased in a sediment tube, which may obscure chaetae.
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Figure 5. Aulodrilus sp. have pseudopenes when mature. These lack a penish sheath or a cuticle and may be hard to see in most circumstances.
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Aulodrilus americanus
Taxa description
Aulodrilus americanus Brinkhurst and Cook, 1966 is a freshwater oligochaete worm that is uncommon in the Great Lakes. It is a tubificid worm with dorsal chaetae beginning in II and both dorsal and ventral chaetae are simple-pointed, bifid, or specialized. This genus is known for having distinctive somatic chaetae, which vary from species to species. They have true penes, but often reproduce asexually. They are often found in sediment tubes, which can obscure the features when mounted if not removed. Anterior bundles of A. americanus have up to 10 chaetae that are simple-pointed or bifid with a rudimentary upper tooth. Starting in VI, chaetae become brush-like or palmate without distinct lateral teeth, often with 8 per bundle. A. americanus is commonly found in sediment tubes since they tend to be more permanent than those of other Aulodrilus species.
Distinguishing features
A. americanus is identified mainly by the distinct somatic chaetae which start out as simple-pointed or bifid with a rudimentary tooth and become brush-like or palmate in VI. There are no other worms in the Great Lakes with brush-like chaetae like this. Unlike some of the other species of Aulodrilus, it lacks hair chaetae. It is also very common to be found in sediment tubes, since they tend to be more permanent than other Aulodrilus species.
Habitat
Aulodrilus spp. are found in mesotrophic habitats or locations with weeds. A. americanus tolerates some organic enrichment and can be found in productive habitats.
Lake occurrence
Lakes Erie and Ontario.
Similar species
Unlike many other tubificids, A. americanus does not need to be mature in order to be identified. This species is quite distinctive, but it could be confused with other species from Aulodrilus. If there is a sediment tube on the mounted worm, it may be possible to see the simple-pointed or minutely bifid anterior chaetae but be unable to see the specialized chaetae posteriorly through the sediment tube. It should also be possible to see hair chaetae through the sediment tube, and if there are it might be A. pluriseta or A. pigueti. If there are no hair chaetae, it may be A. americanus or A. limnobius. A. limnobius is usually smaller than A. americanus but it doesn’t have simple-pointed or minutely bifid chaetae anteriorly. Instead, the anterior chaetae of A. limnobius have the upper tooth shorter and thinner than the lower. Posteriorly, A. limnobius has chaetae expanded laterally to form an oar shape with the upper tooth a small dot at the apex. When they are not in a sediment tube, the difference in the specialized posterior chaetae should be distinct. Lastly, A. paucichaeta also lacks hair chaetae but has bifid chaetae with short upper teeth becoming solitary and very thick with large recurved lower teeth posteriorly. A. paucichaeta is not usually found in the Great Lakes region.
There are a few other worms that have simple-pointed or minutely bifid chaetae anteriorly, but only one other has brush-like chaetae. Telmatodrilus vejdoskyi has simple-pointed chaetae anteriorly that become brush-like with multiple tips. The difference is that T. vejdovskyi has chaetae shaped like a round brush, while A. americanus has chaetae shaped like a broad, flat brush. T. vejdovskyi is located only in western North America and won’t likely be found in the Great Lakes. It isn’t known for having sediment tubes.
Thalassodrilus hallae is a very small tubificid (less than 4 mm) that has bifid chaetae with short, thin upper teeth anteriorly and simple-pointed chaetae posteriorly. A. americanus is usually much bigger, and instead is more likely to have simple-pointed chaetae in the first few segments and has broadly brush-like chaetae posteriorly. T. hallae doesn’t have sediment tubes, and it has penial chaetae on XI instead of penes on X.
Similar to A. americanus, Branchiura sowerbyi is also a large tubificid with chaetae with short, thin upper teeth (sometimes replicate teeth or simple-pointed), but it also has hair chaetae, posterior gill filaments, and lacks brush-like chaetae posteriorly. B. sowerbyi does not make robust sediment tubes.
Finally, there may be some resemblance between A. americanus and the lumbriculid S. heringianus. Both are relatively large worms, but S. heringianus and other immature lumbridulids only have two chaetae with very short upper teeth per bundle, whereas A. americanus has up to 10. S. heringianus has non-retractile penes which are much longer than the penes of Aulodrilus, doesn’t have any brush-like chaetae, and doesn’t form robust sediment tubes.
Relative size
A. americanus is a relatively large oligochaete that is the largest species in this genus.
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. 186–187, 184–185, 136, 188–189, 200–201, 198–199, 192–193, 232–233.
Stimpson, K.S., D.J. Klemm, and J.K. Hiltunen. 1982. A Guide to the Freshwater Tubificidae (Annelida: Clitellata: Oligochaeta) of North America. pp. 29, 44.