Faxonius immunis

(Hagen, 1870)

papershell crayfish

Orconectes immunis, commonly known as the papershell crayfish, is a freshwater crayfish native to central North America that has become in parts of Canada. The has been documented in southwestern Ontario and Lake of the Woods, where it shows preferences for shallow waters with fine substrates and aquatic vegetation. Reproductive studies indicate significant mortality during incubation, with females exhibiting size-dependent . The species has been subject to cellular-level studies of , demonstrating intracellular synthesis in .

Faxonius immunis Schere by Lorenz Seebauer. Used under a CC BY-SA 4.0 license.

Pronunciation

How to pronounce Faxonius immunis: /ɔːr.kəˈnɛk.tiz ˈɪm.juː.nɪs/

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Habitat

Shallow freshwater with organic and inorganic fine substrates. Abundance is negatively correlated with water depth, with highest catch rates in waters shallower than the thermocline. Strongly associated with areas containing macrophytes (aquatic vegetation); catch per unit effort is significantly higher near macrophytes compared to areas without aquatic plants.

Distribution

Native to central North America. Documented in southwestern Ontario, Canada, and Lake of the Woods, Canada, where it is considered . Distribution in Lake of the Woods is limited on islands by water depths near and deeper than the thermocline; islands surrounded by shallower water may facilitate range expansion. GBIF records also indicate presence in Germany (Europe), suggesting additional introduced range.

Life Cycle

( formation) in involves intracellular synthesis of proteinaceous yolk via rough , with transport through smooth endoplasmic reticulum to form mature yolk globules over approximately 7 days. Oocytes synthesize yolk proteins directly rather than incorporating significant maternal blood proteins.

Behavior

Shows selection patterns: negative correlation between abundance and water depth, indicating preference for shallower water. Higher abundance documented in areas with aquatic vegetation compared to unvegetated areas.

Ecological Role

in Lake of the Woods, Canada, where its abundance is negatively correlated with both Orconectes virilis and Orconectes rusticus. As a crayfish, likely contributes to nutrient cycling and serves as prey for fish and other in its native range.

More Details

Reproductive biology

Females exhibit three distinct measures: potential fecundity (ovarian count), realized fecundity (pleopodal/abdominal egg count after extrusion), and actual fecundity (hatched young). Significant egg mortality occurs during incubation, with a 58% decline from abdominal egg counts to hatched juveniles observed in the Ontario . Larger females have higher absolute fecundity at all stages.

Taxonomic note

Currently accepted as Faxonius immunis (Hagen, 1870) in some taxonomic treatments, though Orconectes immunis remains widely used. The Orconectes has been split, with many transferred to Faxonius.