''Pakucaris'' is an extinct genus of bivalved arthropod known from a single species, ''Pakucaris apatis'', found in the Marble Canyon locality of the

Burgess Shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fos ...

in British Columbia, Canada. It is thought to be a member of

Hymenocarina Hymenocarina is an Order (biology), order of extinct marine arthropods known from the Cambrian. They possess bivalved carapaces, typically with exposed posteriors. Members of the group are morphologically diverse and had a variety of ecologies, i ...

. Unlike other members of that group, the posterior segments are covered with a separate

pygidium The pygidium (: pygidia) is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. In groups other than insects, it contains the anus and, in females, the ovipositor. It is compos ...

shield, covergent on other arthropods like artiopods. Specimens range in length from . The main bivalved carapace covers around 80% of the body, with the pygidium covering the remaining 20%. The head has a forward and downward facing pair of moderately sized eyes on short stalks, along with three pairs of cephalic appendages. The thorax has either 30-35 or 70-80 segments, depending on the specimen, while the pygidium has either 11-13 or 20 segments. The segments of the thorax and pygidium have pairs of thin filamentous limbs divided into 20/21 podomeres, with paddle-like

exopod The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip (a ...

s. It was probably nektobenthic (actively swimming close to the seafloor), and its ecology was likely that of a selective

suspension feeder Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a spec ...

, using its limbs to scrape and/or suspend food particles from the sea floor, before using its limbs to capture and transfer them to the mouth.

References

{{Taxonbar, from=Q113580285 Prehistoric arthropod genera Cambrian arthropods Cambrian arthropods of North America Cambrian Canada Fossils of Canada Burgess Shale fossils Hymenocarina Fossil taxa described in 2021