''Surusicaris'' is an extinct genus of bivalved arthropod, known from the

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

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 ...

of British Columbia, Canada. It is considered to be closely related to ''

Isoxys ''Isoxys'' (meaning "equal surfaces") is a genus of extinct bivalved Cambrian arthropod; the various species of which are thought to have been freely swimming predators. It had a pair of large spherical eyes (which are the most commonly preserve ...

,'' and like it has spined grasping frontal appendages.

Description

The only known specimen (ROM 62976), has a roughly semicircular bivalved carapace, which is approximately long and tall. The head has a pair of rounded eyes, and a pair of upward-curling segmented frontal appendages with at least five segments, the second, third and fourth of which bear a spine, with three long spines and at least one short spine on the fifth and terminal segment. The head also has three pairs of other limbs, which are stubby, uniramous (single-part) and unsclerotised, with an annulated appearance, which are tipped with bifid claws. Along the trunk are 12 pairs 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, ...

(two-branched) limbs, which taper in size posteriorly. Their morphology is simple, the morphology of the endopod (the inner, leg-like limb branch) is similar to those of the three uniramous head limbs, while the exopod (the outer limb branch) is sub-lobate, elongate, and possibly flattened, with marginal

setae In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae ...

(hair-like structures) and about the same length as the endopod. The posterior is poorly preserved, but may be a tail-piece formed by two lobes or a fan.

Taxonomy and ecology

''Surusicaris'' has been placed as a member of

Isoxyida Isoxyids are members of the order Isoxyida and the family Isoxyidae, a group of basal arthropods that existed during the Cambrian period. It contains two genera, ''Isoxys'', with 20 species found worldwide, and ''Surusicaris'' known from a single ...

and Isoxyidae, both of which contain only one other genus, ''

''. Isoxyids are considered to be basal stem-group arthropods. Isoxyids are thought to have been actively swimming predators.

References

{{Taxonbar, from=Q115708080 Burgess Shale fossils Cambrian arthropods Burgess Shale animals

Description

Taxonomy and ecology

See also

References