Pristina aequiseta

Pristina aequiseta Bourne, 1891 is a freshwater oligochaete worm that is an uncommon oligochaete in the Great Lakes. It is a naidid worm with dorsal and ventral bundles beginning in II, hair chaetae in the dorsal bundles, and a proboscis. There are 1–2 finely hispid hair chaetae and 1–2 bifid needles with short teeth per dorsal bundle. Ventral bundles contain 5–8 chaetae that change shape with position: those of II are longer and thinner than the rest with the upper tooth twice as long as the lower; chaetae of III–VII have upper teeth only slightly longer than the lower; VIII and posterior have chaetae that are thicker, more curved, with equally long teeth. There are also enlarged chaetae that are very thick that sometimes replace those in IV, V, and/or VI. When mature, genital chaetae appear in VI or VI and VII. Pristina foreli and P. evelinae may be synonymous. This genus was separated into two by Brinkhurst (1985) based on the presence (Pristina) or absence (Pristinella) of a proboscis, although Collado and Schmelz (2000) later suppressed this and recombined them based on their research.

P. aequiseta is identified mainly by the proboscis and dorsal bundles starting in II with hispid hairs and bifid needles with short teeth. The ventral chaetae change shape from having the upper tooth twice as long as the lower to being thick with equally long teeth, and there may be thick enlarged chaetae in IV, V, and/or VI.

Lakes Erie, Michigan, and Ontario.

P. aequiseta most closely resembles other Pristina species with proboscises, especially those with simple-pointed or bifid needles with short teeth. The closest would be P. proboscidea, which has simple pointed needles and hispid hairs, but the ventral chaetae don’t change and the upper tooth is longer than the lower. However, P. proboscidea is not well documented in North America and unlikely to be found in our samples. The next most likely is P. longiseta or P. leidyi, which both have elongated hairs in III so should be easy to separate from P. aequiseta.

Worms that feature proboscis can sometimes have them torn off. Of the Pristina spp. without a proboscis, there is a species complex with dorsal chaetae starting in II with hairs, no elongate hairs, and needle teeth that are short and bifid or pectinate (P. osborni) but they have smooth hair chaetae, not hispid. P. osborni has not been found in our samples.

Pristina species can be confused with a different family of oligochaetaes, Opistocystidae. Opistocystids are small like naidids, have a proboscis, and have hair chaetae and simple-pointed needles starting in II, but are differentiated by having three ciliated appendages on the posterior end. Opistocystids are much rarer than naidid worms and are not found in the Great Lakes region.

P. aequiseta 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. pp. 58–59, 56, 60–61, 36, 90, 94–99, 22, 28.

Hiltunen, J.K., and D.J. Klemm. 1980. A Guide to the Naididae (Annelida: Clitellata: Oligochaeta) of North America. pp. 13, 36.

Brinkhurst, R.O. 1985. The generic and subfamilial classification of Naididae (Annelida: Oligochaeta). Proceedings of the Biological Society of Washington 98(2): 470-475.

Collado, R., and R.M. Schmelz. 2000. Pristina silvicola and Pristina terrena spp.nov., two new soil-dwelling species of Naididae (Oligochaeta, Annelida) from the tropical rain forest near Manaus, Brazil, with comments on the genus Pristinella. Journal of Zoology, London 252: 509-516.”

Wetzel, M.J., R.D. Kathman, S.V. Fend, and K.A. Coates. (2025). Classification and checklist of the freshwater oligochaetes occurring in North America north of Mexico. Mark J. Wetzel.