''Asaphus'' () is a genus of

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

s that is known from the Lower (upper Arenig) and Middle

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

of northwestern Europe (Sweden, Estonia, Saint Petersburg Area).

Etymology

The generic name is derived from the Greek word ''asaphes'', meaning "indistinct."

Description

The headshield (or cephalon) and tailshield (or

pygidium The pygidium (plural 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 compo ...

) are semicircular and without a border (defined by a furrow or a change in convexity parallel to its margin). The cephalon is of approximately equal size as the pygidium (or isopygous). The central raised area of the cephalon (or

glabella The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior to ...

) is long, reaching the frontal margin. It may have faint lateral glabellar furrows or be smooth, and sometimes an inconspicuous tubercle is present just in front of the hardly discernible occipital ring. The natural fracture lines (sutures) of the head run along the top edges of the compound eye. From the back of the eye these cut to the back of the head (or is said to be opisthoparian) and not to the side. The free cheeks (or librigenae) are separated from each other anteriorly by a suture at the midline. The corner between the side and the back of the cephalon (or genal angle) is rounded or (in a few species) pointed into spines. Eyes holochroal, commonly more or less conical, short or moderate in length. In some evolution lines, the visual surface of the eye is raised on a stalk. The lateral corners of the palate (or hypostome), visual from the

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

side, are more or less protruding, and the posterior part is forked with two triangular teeth. The reflexed margin of the exoskeleton (or doublure) is broad. The articulate midlength part of the body (or

thorax The thorax or chest is a part of the anatomy of humans, 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 divisions of the cre ...

) consists of 8 segments. Furrows in the parts outside the axis (or pleural furrows) are diagonal. The pygidium is rounded, and has a long axis with concave, posteriorly parallel sides. Some rings may be faintly defined anteriorly and the axis dissolves in the postaxial field. The areas outside the axis (or pleural fields) are smooth or very faintly ribbed.

Diversity

* '' A. expansus'' (Wahlenberg,

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(

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

) synonyms '' Entomostracites expansus'', '' Entomolithus paradoxus α expansus'' * ''A. acuminatus'' Boeck, 1838 * ''A. bottnicus'' Jaanusson * ''A. broeggeri'' Schmidt, 1898 * ''A. cornutus'' Pander, 1830 * ''A. eichwaldi'' Schmidt * ''A. heckeri'' (Ivantsov) * ''A. holmi'' Schmidt, 1898 * ''A. ingrianus'' Jaanusson, 1953 * ''A. intermedius'' Lessnikova in Balashova, 1953 * ''A. knyrkoi'' Schmidt * ''A. kotlukovi'' Lessnikova in Balashova, 1953 * '' A. kowalewskii'' Lawrow, 1856 * ''A. latus'' Pander, 1830 * ''A. laevissimus'' Schmidt, 1898 * ''A. lepidurus'' Neiszkowski, 1859 * ''A. minor'' * ''A. neiszkowskii'' Schmidt, 1898 * ''A. pachyophthalmus'' * ''A. platycephalus'' ( Stokes, 1824) * ''A. plautini'' Schmidt, 1898 * ''A. punctatus'' Lessnikova, 1949 * ''A. raniceps'' Dalman, 1827 * ''A. robustus'' * ''A. sulvevi'' Jaanusson * ''A. vicarius'' (Toernquist, 1884) * ''A. wahlenbergi''

Species previously assigned to ''Asaphus''

As the genus ''Asaphus'' was established early, many species have since been reassigned to genera in various trilobite orders. * ''A. angustifrons'' = '' Ptychopyge angustifrons'' * ''A. armadillo'' = '' Nileus armadillo'' * ''A. aspectans'' = '' Coronura aspectans'' * ''A. barrandei'' = '' Basilicus barrandei'' * ''A. brongniarti'' = '' Eohomalonotus brongniarti'' * ''A. canadensis'' = '' Pseudogygites canadensis'' * ''A. cawdori'' = '' Acaste cawdori'' * ''A. corndensis'' = '' Ogyginus corndensis'' * ''A. debuchii'' = '' Ogygiocarella debuchii'' * ''A. devexus'' = '' Xenasaphus devexus'' * ''A. duplicatus'' = '' Platycalymene duplicatus'' * ''A. eichwaldi'' = '' Bollandia eichwaldi'' * ''A. extans'' = '' Bathyurus extans'' * ''A. fischeri'' = '' Pliomera fischeri'' * ''A. frontalis'' = '' Niobe frontalis'' * ''A. gemmuliferus'' = '' Phillipsia gemmulifera'' * ''A. globiceps'' = '' Bollandia globiceps'' * ''A. granuliferus'' = '' Bollandia globiceps'' * ''A. hausmanni'' = '' Odontochile hausmanni'' * ''A. homfrayi'' = '' Asaphellus homfrayi'' * ''A. latifrons'' = '' Stygina latifrons'' * ''A. nasutus'' = '' Neoprobolium nasutus'' * ''A. obsoletus'' = '' Bollandia obsoleta'' * ''A. palpebrosus'' = '' Symphysurus palpebrosus'' * ''A. plicicostis'' = '' Plectasaphus plicicostis'' * ''A. praetextus'' = '' Ogmasaphus praetextus'' * ''A. selenourus'' = '' Odontocephalus selenourus'' * ''A. seminiferus'' = '' Eocyphinium seminiferum'' * ''A. seticornis'' = '' Tretaspis seticornis'' * ''A. stacyi'' = '' Homalopyge stacyi'' * ''A. stokesii'' = '' Warburgella stokesii'' * ''A. subcaudatus'' = '' Acaste subcaudata'' * ''A. truncatulus'' = '' Phillipsia truncatula'' * ''A. tyrannus'' = '' Basilicus tyrannus''

References

External links

*
drawings of many ''Asaphus'' species

Website of the Saint-Petersburg Paleontological Laboratory

{{Taxonbar, from=Q778590 Asaphida genera Ordovician trilobites of Europe Fossils of Estonia Fossils of Russia Fossils of Sweden Early Ordovician first appearances Middle Ordovician extinctions Taxa named by Alexandre Brongniart Floian Dapingian Darriwilian