Emucarididae is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of soft-shelled

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

-like

arthropods 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 ...

(

nektaspid Nektaspida (also called Naraoiida, Nektaspia and Nectaspida) is an extinct order of non- mineralised artiopodan arthropods. They are known from the lower-Cambrian to the upper Silurian. Originally classified as trilobites, which they superficiall ...

s) from the

Lower 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 Ordovici ...

South Australia South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. With a total land area of , it is the fourth-largest of Australia's states and territories by area, which in ...

and South China. It contains only two genera – '' Emucaris'' and '' Kangacaris''. Two species were described in 2010 from specimens recovered from

Emu Bay Shale The Emu Bay Shale is a Formation (stratigraphy), geological formation in Emu Bay, South Australia, containing a major Konservat-Lagerstätte (fossil beds with soft tissue preservation). It is one of two in the world containing Redlichiidan trilob ...

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 ...

'', one species in 2012 from the

Maotianshan Shales The Maotianshan Shales () are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation or Heilinpu Formation, famous for their '' Konservat Lagerstätten'', deposits known for the exceptional preservation of fossilized orga ...

. It is classified under the order

Nektaspida Nektaspida (also called Naraoiida, Nektaspia and Nectaspida) is an extinct order of non- mineralised artiopodan arthropods. They are known from the lower-Cambrian to the upper Silurian. Originally classified as trilobites, which they superficiall ...

, and is a sister-group to the families Liwiidae and

Naraoiidae Naraoiidae is a family, of extinct, soft-shelled trilobite-like arthropods, that belongs to the order Nektaspida. Species included in the Naraoiidae are known from the second half of the Lower Cambrian to the end of the Upper Silurian. The total ...

Description

The Emucarididae have a non-calcified exoskeleton that consists of an articulating head shield (or

cephalon Cephalon, Inc. was an American biopharmaceutical company co-founded in 1987 by pharmacologist Frank Baldino Jr., Frank Baldino, Jr., neuroscientist Michael Lewis, and organic chemist James C. Kauer—all three former scientists with the DuPont ...

thorax The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of mammals and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main di ...

and tail shield (or

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 ...

), and there are no constrictions where these parts meet. The cephalon is semi-circular and has a straight back margin. The thorax consists of 3 or 4 narrow segments. The pygidium is 1-2× as long as the cephalon and has a distinct border furrow. The mouth plate (or hypostome) that sits on the belly-side of the cephalon is elongated and divided by a straight left-to-right suture. The frontal portion is approximately square with two pointed horns that extend from the frontal margin to the sides (like in a capital T), the back portion is longer than wide with a round back margin. The pair of relatively short

antennas In radio-frequency engineering, an antenna (American English) or aerial (British English) is an electronic device that converts an alternating electric current into radio waves (transmitting), or radio waves into an electric current (receivi ...

are implanted behind the horns of the hypostome and stick out to the sides. There appear to be three pairs of limbs under the cephalon, carrying side branches with bristle-like gills (or setae).

References

Nektaspida Cambrian first appearances Cambrian extinctions Trilobite families {{nektaspida-stub