Portunites incerta
Portunites incerta
Common name
Swimming Crab
Fossil group
Crustaceans
Order
Decapoda
Family
Polybiidae
Genus
Portunites
Taxonomic status
Accepted
Geological age
Ypresian
Summary
Portunites incerta was a swimming crab. Compared with more heavily built bottom-walking crabs, swimming crabs have broad, streamlined bodies and are adapted for more active movement across the seabed and through the water just above it.
It was probably a fast opportunistic predator and scavenger, taking worms, molluscs, smaller crustaceans and carrion. In the London Clay ecosystem it would have filled a more mobile hunting niche than sponge crabs, stalked barnacles or slow-moving spider crabs.
Quick Identification
Look for: a broad, flattened Portunites carapace with conspicuous lateral teeth; compare the complete margins and dorsal pattern with Portunites stintoni rather than using size alone.
Diagnostic Features
- Carapace broad and relatively flattened.
- Anterolateral margins bear a series of conspicuous teeth.
- Dorsal regional relief is lower than in strongly vaulted dromiid crabs.
- Frontal and orbital margins contribute important Species-level characters.
- Separation from Portunites stintoni requires the combined carapace outline, marginal teeth and ornament.
Fossil Details
Typical size
Centimetre-scale carapace; published material varies and size alone is not diagnostic.
Fossil material
Carapace, Claw / Chela
Preservation
Lateral teeth and frontal margins are commonly broken. Flattening may exaggerate the swimming-crab profile, while abrasion can remove fine dorsal ornament.
Similar Species
Recorded Fossil Sites
London Clay Formation
Thames Group
Synonyms & Previous Names
Leiochilus morrisi
References
- Hiroaki Karasawa; Carrie E. Schweitzer; Rodney M. Feldmann. (2008). Revision of Portunoidea Rafinesque, 1815 (Decapoda: Brachyura) with emphasis on the fossil genera and families. Journal of Crustacean Biology, 28(1), 82–127 View reference
- J. S. H. Collins; C. J. T. Mellish; A. J. Ross; P. R. Crabb; S. K. Donovan. (2020). A guide to the fossil Decapoda (Crustacea: Axiidea, Anomura, Brachyura) of the British Isles. Proceedings of the Geologists' Association, 131(1), 19–50 View reference
- Thomas Bell. (1857). A monograph of the fossil malacostracous Crustacea of Great Britain. Part I. Crustacea of the London Clay. Monograph of the Palaeontographical Society, 10, i–viii, 1–44. Palaeontographical Society, London View reference
Last Reviewed
12 August 2026
Reviewed by
Sam Harris