Ripistes parasita

Ripistes parasita (Schmidt, 1874) is a non-native freshwater oligochaete worm from Europe and Lake Baikal that is uncommon in the Great Lakes. It is a naidid worm with dorsal bundles starting in VI and ventral bundles beginning in II, hair chaetae, and usually having a proboscis, although it may be broken. R. parasita has 2–16 giant hair chaetae in the dorsal bundles of VI–VIII, accompanied by 2–6 short hairs, and 10–18 straight simple-pointed needles without a nodulus. Posterior dorsal bundles have 1–3 shorter, more robust, and possibly hispid hairs alongside fewer needles. The giant hairs are more than three times as long as the shorter hairs in IX and on. Ventral chaetae begin in II and often have a single bend at the proximal end. There are 2–7 ventral chaetae in II and III with the upper tooth longer than the lower, and II may be longer and more robust than III. The ventral chaetae of IV and V are typically absent. The ventral bundles from VI and posterior have 3–8 thicker chaetae with the upper teeth shorter than the lower, and the nodulus is more distal than the proximal nodulus of II and III. It may or may not have eyes.

R. parasita is identified by the giant dorsal hairs in VI–VIII with numerous simple-pointed needles, absent ventrals in IV and V, and a proboscis. Sometimes the giant hairs are missing, but there are still more needles in VI–VIII than posteriorly. If this occurs, the missing ventral chaetae can help with identification. There are sometimes a few ventral chaetae in IV, but none in V. This species usually has a proboscis but in practice the proboscis may be torn off or obscured when mounted. In that case, rely on the chaetae.

This species has been found in the Great Lakes (Superior, Huron, and Michigan) according to the USGS Nonindigenous Aquatic Species database and in the North Channel of Lake Huron in 2001 and 2022. Minnesota, New York, Wisconsin.

The features of R. parasita are very distinctive, but there are a few other oligochaetes that could look similar. Arcteonais lomondi, Stylaria lacustris, and S. fossularis all have a proboscis and bundles with hair chaetae starting in VI. A. lomondi has numerous dorsal hairs that often form a tent structure, all crossing at point near the proximal end, but no giant or hispid hairs. R. parasita does not have a tent-shaped cross at the proximal end of the dorsal bundles. A. lomondi’s ventral chaetae are sigmoid with the upper teeth longer and slightly thinner than the lower, while R. parasita’s ventral chaetae have a bend at the proximal end. S. lacustris has a long proboscis starting from between invaginated lobes; S. fossularis has a long proboscis starting from the end of the conical prostomium. The hair chaetae are less numerous in S. lacustris and S. fossularis and they may form a tent shape. The ventral chaetae of S. lacustris have a double-bend at the proximal end, and all are the same length. S. fossularis may only have one bend at the proximal end. None of these species have giant hair chaetae and are not missing ventral chaetae in IV and V.

A few other naidid species have elongated hair chaetae. Slavina appendiculata has dorsal bundles starting in VI with 1–3 elongated hairs in only VI, 1–2 short hairs in the rest, and 1–2 straight needles with hair-like tips. The elongated hairs are only about twice as long as the rest of the hairs, there is no proboscis, and the body wall is papillate with foreign matter attached. Unlike R. parasita, Bratislavia bilongata has dorsal chaetae starting in III with elongated hairs in III only and shorter hairs in the rest. There are only 2 smooth hairs and 2 needles per bundle and no proboscis. A few species of Pristina also have elongated hairs in II or III: P. leidyi, P. longiseta, and P. longisoma. All three have dorsal bundles starting in II, although only up to 4 hairs and needles, which is fewer than R. parasita. P. leidyi and P. longiseta have a proboscis, while P. longisoma does not. Of all these species, S. appendiculata would be the most likely to be confused due to elongated hairs since the chaetal bundles start in VI, not II or III, and the fact that it is commonly found in our Great Lakes samples. P. longiseta has been found in our Great Lakes samples. P. leidyi is not in our samples but is widespread. B. bilongata has only been found in Florida and New Jersey. P. longisoma is only in Arkansas, Florida, and Louisiana. However, none of these species have numerous hairs and needles associated with their elongated chaetae. Most lack a proboscis, and all have ventral chaetae in IV and V.

Lastly, if the proboscis is missing, it will not key out properly. The only other oligochaete with numerous hair chaetae starting in VI is Vejdovskyella. V. intermedia is more likely than V. comata in our samples. V. intermedia lacks eyes and a proboscis, has 4–9 long hispid, bifid hair chaetae and 4–9 simple needles with broad tips, has anterior ventral chaetae decreasing in size to V, single ventral chaetae starting in VI and beyond, VI–VIII may have giant chaetae with thin replicated upper teeth, and there may be foreign matter attached. V. comata has 4–8 hispid hairs and 1–8 simple needles with broad tips that may appear to start in V because there are no ventrals in V, usually has eyes but no proboscis, has anterior ventral chaetae decreasing in size to IV with V and maybe IV absent, 2–3 ventrals starting in VI, occasionally a single giant chaetae with a single thin upper tooth in VI–VIII, and scattered papillae on the body wall. Vejdovskyella spp. are usually very small compared to other naidids, so even though their numerous hairs are long, they still might only be 300µm compared to a 1000µm giant hair from R. parasita. Vejdovskyella spp. also have numerous hairs in each bundle, not just VI–VIII. Despite confusion from the key, it would not be easy to mistake R. parasita for Vejdovskyella.

R. parasita is a small freshwater oligochaete.

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. p. 62–63, 34, 38, 56–61, 78–79, 92–95.

Hiltunen, J.K., and D.J. Klemm. 1980. A Guide to the Naididae (Annelida: Clitellata: Oligochaeta) of North America. pp. 19, 38.

Simpson, K.W., and L.E. Abele. 1984. Ripistes parasita (Schmidt) (Oligochaeta: Naididae), a distinctive oligochaete new to North America. Freshwat. Invert. Biol. 3: 36-41.

USGS Nonindigenous Aquatic Species database entry for Ripistes parasita.

Spencer, D.R., Hudson, P.L. 2003. The Oligochaeta (Annelida, Clitellata) of the St. Lawrence Great Lakes region: an update. J. Great Lakes Res. 29, 89-104.