''Enalikter'' ("scourger of the sea") is an extinct

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 ...

described from the middle

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

Herefordshire Lagerstätte Coalbrookdale Formation, earlier known as Wenlock Shale or Wenlock Shale Formation and also referred to as Herefordshire Lagerstätte in palaeontology, is a fossil-rich deposit (''Konservat-Lagerstätte'') in Powys and Herefordshire at the Engla ...

at the

England–Wales border The England–Wales border, sometimes referred to as the Wales–England border or the Anglo-Welsh border, runs for from the Dee estuary, in the north, to the Severn estuary in the south, separating England and Wales. It has followed broadly ...

in UK. This genus is known from only one species, ''E. aphson''. ''Enalikter'' is described as late-living example of

Megacheira Megacheira ("great hands", also historically great appendage arthropods) is an extinct class of predatory arthropods defined by their possession of spined "great appendages". Their taxonomic position is controversial, with studies either consider ...

, "great-appendage arthropod". It subsequently suggested to be an

annelid The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to vario ...

by other researchers, however subsequent studies rejected this interpretation. Its interpretation as megacheiran arthropod has been questioned in later studies.

Morphology

Enalikter_aphson_reconstruction_as_arthropod

''Enalikter'' is small arthropod with length just around long. Head shield is subrectangular and lacked eyes. Median, unpaired antenna and three pairs of appendages can be seen on head, and a first appendage had three tapering

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

. Twelve trunk segments lack

tergites A ''tergum'' (Latin for "the back"; : ''terga'', associated adjective tergal) is the dorsal ('upper') portion of an arthropod segment other than the head. The anterior edge is called the 'base' and posterior edge is called the 'apex' or 'margin'. ...

, and is flexible to bend at least 90 degrees. Trunk appendages are

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, ...

. The egg-shaped

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 ...

had two pairs of blade-like processes.

Classification

''Enalikter'' is probably related to '' Bundenbachiellus'', a larger arthropod genus from later Early Devonian

Hunsrück Slate The Hunsrück () is a long, triangular, pronounced upland in Rhineland-Palatinate, Germany. It is bounded by the valleys of the Moselle-Saar (north-to-west), the Nahe (south), and the Rhine (east). It is continued by the Taunus mountains, past ...

of Germany, due to morphological similarities between the two genera, though the taxa are clearly distinct. The two genera constitute the family

Enaliktidae Enaliktidae is an extinct family of elongate arthropods known from the Silurian and Devonian periods, containing two genera, '' Enalikter'' and '' Bundenbachiellus.'' The taxonomic position of the family is uncertain. In its original description ...

. The original description suggested that Enaliktidae belonged to

, a group of arthropods with similar looking cephalic appendages. However, in 2015, other researchers questioned its affinity as arthropod, and considering from characters like lack of tergites, flexible trunk segments, and unpaired antenna, it is considered that is more likely to be an

. This hypothesis was rejected by two later studies, because these characters are also known from various arthropod taxa, in addition there are features that demonstrate an arthropod affinity, like ventrally placed mouth and J-shaped gut. Moreover, the characters that used to diagnose as annelids by these researchers are taken from different annelids, and there is no one annelid taxon that shares these characteristics. Although it is likely to be an arthropod, its affinity as megacheiran is still questioned, due to the fact that homology between the cephalic appendages of the two groups is unclear.

References

{{taxonbar, from=Q112811603 Silurian arthropods of Europe Silurian England Fossils of England Fossil taxa described in 2014 Megacheira