''Koonaspides'' is an extinct genus of fossil

crustacean 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 ...

in the family

Anaspidesidae Anaspidesidae is a family of freshwater crustacean that is endemic to Tasmania, Australia. The family contains 3 living genera. This group of crustaceans are considered living fossils. They are commonly and collectively known as the Tasmanian ana ...

, from

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

(

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

) Koonwarra Fossil Beds in eastern

Victoria Victoria most commonly refers to: * Queen Victoria (1819–1901), Queen of the United Kingdom and Empress of India * Victoria (state), a state of Australia * Victoria, British Columbia, Canada, a provincial capital * Victoria, Seychelles, the capi ...

, Australia. The only known species within the genus is ''Koonaspides indistinctus''.P. A. Jell and P. M. Duncan. 1986. Invertebrates, mainly insects, from the freshwater, Lower Cretaceous, Koonwarra Fossil Bed (Korumburra Group), South Gippsland, Victoria. ''Memoirs of the Association of Australasian Palaeontologists'' 3:111-205 Along with the Triassic genus '' Anaspidites'', this is one of two known fossil members of this family.

Discovery and etymology

A single specimen of ''K. indistinctus'', NMV P102799 is known from the Koonwarra Fossil Beds. The genus name consists of Koon- from Koonwarra and -aspides from Greek ''aspis'', a shield. The species name ''indistinctus'' means obscure or dim.

Description

The only known specimen of ''K. indistinctus'' has a body length of , with indistinct antennae preserved as long as . Its eyes are large and very widely separated with eye stalks. Head and anterior part of thorax are indistinct, three posterior tergites could be recognized, but those are shorter and apparently much less

sclerotized Sclerosis (also sclerosus in the Latin names of a few disorders) is a hardening of tissue and other anatomical features. It may refer to: * Sclerosis (medicine), a hardening of tissue * in zoology, a process which forms sclerites, a hardened exo ...

than abdominal ones. Although very indistinct, long and slender thoracic appendages are confirmed, some reaching around half length of thorax. The abdomen has six segments, with the five anterior ones of almost equal length, with ventral tip of tergites bluntly pointed. The sixth segment is narrower and longer than other five, and the

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 ...

is almost as long. The telson has scalloped lateral margins and distinct border furrows on each side.

Endopodite 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, : ...

s are visible on abdominal tergites, being compressed similar to that of ''

Anaspides ''Anaspides'' is a genus of freshwater crustaceans in the family Anaspidesidae. The genus was first described in 1894 by George Malcolm Thomson. The genus was originally placed in the family, Anaspididae by Thomson, but this genus name was preo ...

''. The sixth abdominal segment bears large

uropod Uropods are posterior appendages found on a wide variety of crustaceans. They typically have functions in locomotion. Definition Uropods are often defined as the appendages of the last body segment of a crustacean. An alternative definition sugge ...

s which have hairy margin. Preserved tergites are penetrated by many circular holes, destroying details of the cuticle. This may be because of escaping gases from compaction of body, or sediment rupturing the cuticle. Preservation also suggests that cuticle is extremely thin.

Classification

The lack of a carapace and morphology of abdominal segment suggests that ''Koonaspides'' is a member of

Syncarida Syncarida is a superorder of crustaceans, comprising the two extant order (biology), orders Anaspidacea and Bathynellacea, and the extinct order Palaeocaridacea. Taxonomy Fifty-nine living genera are known, in six families: ;Anaspidacea Calman, ...

, with its stalked eyes, pleopod morphology and general morphological similarities with '' Anaspidites'' suggesting that it is a member of Anaspidesidae, the family previously called as Anaspididae. Modern anaspidesids are endemic to

Tasmania Tasmania (; palawa kani: ''Lutruwita'') is an island States and territories of Australia, state of Australia. It is located to the south of the Mainland Australia, Australian mainland, and is separated from it by the Bass Strait. The sta ...

, which suggests the current distribution of that family represents a relict endemism, originated from earlier members like Triassic ''Anaspidites''. ''Koonaspides'' and ''Anaspidites'' possibly show that this group lived in southeastern Australia for at least 200 million years.

Paleoecology

''Koonaspides'' is known from

Koonwarra Fossil Beds in Victoria, which represents a freshwater

lacustrine A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...

environment in the polar regions of

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

. Some algae microfossils and many plant macrofossils are known, insects of many groups including the stem-

flea Flea, the common name for the order (biology), order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by hematophagy, ingesting the blood of their hosts. Adult f ...

Tarwinia ''Tarwinia'' is an extinct genus of stem-group flea known from a single species, ''T. australis'', from the Early Cretaceous (Aptian) Koonwarra Fossil Bed of Victoria Victoria most commonly refers to: * Queen Victoria (1819–1901), Queen ...

'', other arthropods like freshwater xiphosuran '' Victalimulus'', and other fauna including fish are known from this fossil site. Other crustaceans known from Koonwarra are

conchostracan Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated Bivalvia, bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally ...

''Cyzicus'' ('' Lioestheria'') ''banchocarus'' and anostracan '' Koonwarrella'', as well as

ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant taxon, extant) have been identified,Brandão, S.N.; Antoni ...

References

{{Taxonbar, from=Q131554201 Syncarida Early Cretaceous arthropods Cretaceous arthropods of Australia Fossil taxa described in 1986