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

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

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 foss ...

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 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, plu ...

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, plu ...

limbs, which taper in size posteriorly. Their morphology is simple, the morphology of the

endopod 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 (anat ...

is similar to those of the anterior three uniramous head limbs, while the

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, plur ...

is sub-lobate, elongate, and possibly flattened, with marginal

setae In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. Th ...

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 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

{{reflist Burgess Shale fossils Cambrian arthropods Burgess Shale animals