Dinocaridida

Dinocaridida is an extinct group of mostly Cambrian swimming stem-group arthropods, including radiodonts and other animals with grasping frontal appendages.

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Stem-group: An evolutionary grouping containing extinct relatives closer to a crown group than to any other living group, but outside that crown group. Dinocarididans lie on the arthropod stem rather than within the living arthropod crown.
Biramous appendage: An appendage divided into two branches, often combining a limb-like branch with an outer flap. Some dinocarididans had paired trunk flaps associated with swimming and respiratory exchange.
Opabinia: A small Cambrian animal with five eyes, a segmented body, and a flexible frontal proboscis. Its unusual anatomy illustrates the diversity of early dinocarididan forms.
Cambrian explosion: A geologically brief interval when animal diversity and complexity expanded markedly, beginning about 539 million years ago. Dinocarididans diversified during this major early radiation of animal life.
Trilobite: An extinct marine arthropod with a three-lobed exoskeleton, abundant in Paleozoic fossil deposits. Trilobites belong to the arthropod crown group, unlike dinocarididans on its stem.
Radiodonta: An extinct order of stem-group arthropods with segmented frontal appendages and circular, toothed mouths. Radiodonts are the best-known major subgroup within Dinocaridida.
Cambrian swimming: Active movement through Cambrian seas by animals using body undulations, appendages, or fin-like structures. Dinocarididan trunk flaps and lateral lobes powered movement through the water.
Hurdia: A Cambrian radiodont distinguished by a large head carapace and grasping frontal appendages. Its preserved head structures help distinguish radiodont body plans.
Burgess Shale: A Middle Cambrian fossil deposit in British Columbia preserving soft-bodied marine organisms in exceptional detail. Its fossils preserve many of the group’s best-known anatomical details.
Megacheira: An extinct group of arthropods with large, grasping head appendages bearing multiple segments. Megacheirans also had prominent frontal limbs, but their body plans differ from radiodonts.