Portunoidea is a superfamily of true crabs (infraorder Brachyura) within the subsection Heterotremata. The group was established by Constantine Samuel Rafinesque in 1815 and is best known for including the family Portunidae, the swimming crabs. The composition of the superfamily has been subject to ongoing revision, particularly in light of molecular phylogenetic studies, which have led to differing opinions on which additional crab families belong within Portunoidea.
Description
Members of Portunoidea generally possess a relatively flat, smooth carapace that is wider than it is long. The carapace shape ranges from hexagonal or sub‑hexagonal to rectangular or transversely ovate, and it is often widest near the hindmost spines of the forward rim. Some species bear up to nine pairs of these spines, while others lack them entirely. Typical morphological features include:
- A lobed endopod on the first maxilliped, forming the characteristic “portunid lobe.”
- Robust chelipeds (claw-bearing legs).
- In many taxa, the last pair of pereiopods (walking legs) ends in ovate dactyls.
- Incomplete sutures of the sternum between segments 4 to 8; in Portunidae, the eighth sternite is usually visible ventrally and carries a penial groove.
- Males exhibit either completely free abdominal somites or fused somites 3–5 that often retain sutures.
- The first gonopod (male reproductive appendage) is strongly curved with a swollen, hooked base.
Classification
Portunoidea is closely related to the superfamily Xanthoidea. The exact family composition varies among taxonomic treatments, but current classifications recognize thirteen families, four of which are extinct. Representative families include:
- Portunidae (swimming crabs) – the most prominent extant family.
- Geryonidae – deep‑sea crabs, sometimes placed in Xanthoidea.
- Carcinidae
- Ovalipidae
- Pirimelidae
- Polybiidae
- Thiidae
- Hexapodidae and Mathildellidae – occasionally included, though sometimes assigned to Xanthoidea.
- Trichodactylidae – freshwater crabs, occasionally listed within Portunoidea.
Extinct families documented from the fossil record include †Carcineretidae, †Litophylacidae, †Longusorbiidae, and †Psammocarcinidae.
Phylogeny and Systematics
The internal relationships of Portunoidea have been investigated using both traditional morphological characters and molecular data. Recent phylogenetic analyses suggest that several families traditionally placed in other superfamilies (e.g., Xanthoidea) may be more appropriately nested within Portunoidea, while some groups historically assigned to Portunoidea may be better situated elsewhere. Consequently, the superfamily’s composition remains provisional pending further systematic research.
Distribution and Ecology
All extant Portunoidea inhabit marine environments, ranging from shallow coastal waters to deep‑sea habitats. The family Trichodactylidae, when included, represents a notable freshwater lineage. Members are typically omnivorous or predatory, with many portunid species exhibiting strong swimming abilities facilitated by flattened, paddle‑like fifth pereiopods.
References
- De Grave, S.; Pentcheff, N. D.; Ahyong, S. T.; et al. (2009). “A classification of living and fossil genera of decapod crustaceans.” Raffles Bulletin of Zoology, Supplement 21: 1–109.
- Karasawa, H.; Schweitzer, C. E. (2006). “A new classification of the Xanthoidea sensu lato (Crustacea: Decapoda: Brachyura) based on phylogenetic analysis and traditional systematics and evaluation of all fossil Xanthoidea sensu lato.” Contributions to Zoology, 75(1/2): 23–73.
- Boyko, C. B. (2022). “Portunoidea Rafinesque, 1815.” World Register of Marine Species (WoRMS).
This entry reflects the current consensus as of 2024; taxonomic revisions may alter the composition and relationships of the superfamily in the future.