''Musacaris '' is an extinct genus of

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 ...

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

Orsten The Orsten fauna are fossilized organisms preserved in the Orsten lagerstätte of Cambrian (Late Miaolingian to Furongian) rocks, notably at Kinnekulle and on the island of Öland, all in Sweden. The initial site, discovered in 1975 by Klaus M� ...

Lagerstätte A Fossil-Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that preserves an exceptionally high amount of palaeontological information. ''Konzentrat-Lagerstätten'' preserv ...

, formerly synonymous with ''

Martinssonia ''Martinssonia'' is an extinct genus of Cambrian arthropod from the Orsten Lagerstätte. Description ''Martinssonia'' is a small (roughly 1.5 mm long) arthropod, with eight pairs of appendages and ten segments including the eyeless head. It ...

''. It contains only a single species, ''Musacaris gerdgeyeri''.

Description

''Musacaris'' is a small (roughly 0.8 mm long), unsegmented arthropod, with four pairs of appendages. It has a pair of antennae, and three 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, ...

appendages. It also has an unusual projection on its head, possibly the future position of the mouth. The unsegmented body suggests all current specimens of ''Musacaris'' may be so-called "head larvae". The five developmental stages are quite similar, with the same amount and positioning of the limbs. Currently, ''Musacaris'' is thought to be a basal

mandibulate The clade Mandibulata constitutes one of the major subdivisions of the phylum Arthropoda, alongside Chelicerata. Mandibulates include the crustaceans, myriapods (centipedes and millipedes, among others), and all true insects. The name "Mandibulat ...

or stem-

crustacea Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

n, possibly sister to labrophorans (Crustacea and

Phosphatocopina Phosphatocopina (alternatively Phosphatocopida) is an extinct group of bivalved arthropods known from the Cambrian period. They are generally sub-milimetric to a few millimetres in size. They are typically only known from isolated carapaces, but ...

Distribution

''Musacaris'' is known from thirteen specimens of different larval forms, all from the Orsten Lagerstätte in Sweden, alongside twenty-one other specimens referred to ''Martinssonia elongata''.

References

Cambrian arthropods Enigmatic arthropod taxa Fossil taxa described in 2010 {{paleo-arthropod-stub