''Sanctacaris'' is a

Middle Cambrian Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek (di ...

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

from 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 ...

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

. It was most famously regarded as a

stem-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

chelicerate The subphylum Chelicerata (from Neo-Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, ticks ...

, a group which includes

horseshoe crabs Horseshoe crabs are arthropods of the family Limulidae and the only surviving xiphosurans. Despite their name, they are not true crabs or even crustaceans; they are chelicerates, more closely related to arachnids like spiders, ticks, and scorpi ...

spider Spiders (order (biology), order Araneae) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude spider silk, silk. They are the largest order of arachnids and ran ...

s and

scorpion Scorpions are predatory arachnids of the Order (biology), order Scorpiones. They have eight legs and are easily recognized by a pair of Chela (organ), grasping pincers and a narrow, segmented tail, often carried in a characteristic forward cur ...

s, although subsequent

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

studies have not always supported this conclusion. Its chelicerate affinities regain support in later observations, alongside the reassignment of ''

Habelia ''Habelia'' is a genus of extinct arthropod from the Middle Cambrian, thought to be one of the earliest known relatives of chelicerates. Its fossils have been found in the Burgess Shale in British Columbia, Canada. Fifty-four specimens of ''Habel ...

optata'' as a sanctacaridid-related basal chelicerate. It has been placed as a member of the extinct family Sanctacarididae alongside '' Wisangocaris'' and '' Utahcaris''. ''Sanctacaris'' specimens range from 46 to 93 mm in length. The head bears five pairs of grasping appendages (corresponding to chelicerate's

pedipalps Pedipalps (commonly shortened to palps or palpi) are the secondary pair of forward appendages among Chelicerata, chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to ...

and walking legs) and a sixth pair of posterior appendages (correspond to horseshoe crab's chilaria). The grasping appendages each bear an antenna-like exopods. There are 11 body segments, with the former 10 each bearing a pair of

biramous 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, ...

appendages with flap-like exopod and reduced leg-like endopod. There is a broad, flat paddle-like

telson The telson () is the hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment (biology), segment of the arthropod body, or an additional division that is not a true segm ...

. Originally ''Sanctacaris'' was called informally 'Santa Claws'. Its Latin name translates as "saintly crab". Unlike most other Burgess forms, ''Sanctacaris'' is not present in Charles Walcott's 1909 quarry and was discovered at a different level by Desmond Collins in 1980–1981.

Etymology

The generic name "''Sanctacaris'' " is a compound of the Latin words "sanctus" (saint or sacred) and "caris" (meaning crab or shrimp, a common suffix used in aquatic arthropods). The specific name of the type species ''"uncata'' " means "claws" in Latin and is named after the claw-shaped appendages on the head of this species. The name "saint claws" refers to

Santa Claus Santa Claus (also known as Saint Nicholas, Saint Nick, Father Christmas, Kris Kringle or Santa) is a legendary figure originating in Western Christian culture who is said to bring gifts during the late evening and overnight hours on Chris ...

, which was the field name used to refer to ''Sanctacaris''.

Ecology

The robust gnathobases, alongside the fact that fellow sanctacaridid '' Wisangocaris'' has been found with trilobite fragments in its stomach, has led to suggestions that ''Sanctacaris'' was

durophagous Durophagy is the eating behavior of animals that consume hard-shelled or exoskeleton-bearing organisms, such as corals, shelled mollusks, or crabs. It is mostly used to describe fish, but is also used when describing reptiles, including fossil t ...

, feeding on hard shelled organisms.

References

External links

* {{Taxonbar, from1=Q20672511, from2=Q2718204 Prehistoric chelicerates Burgess Shale fossils Fossil taxa described in 1988 Cambrian genus extinctions

Etymology

Ecology

See also

References

External links