Librostoma

Librostoma
Temporal range: Cambrian series 2–Lopingian
Asaphus lepidurus
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: †Trilobita
Subclass: †Librostoma
Fortey, 1990[1]
Orders

Librostoma is a subclass of trilobites defined by having a natant hypostome, which is a hypostome (mineralized trilobite mouthpart) that is free from the anterior doublure and aligned with the anterior of the glabella,[4] this is unlike a conterminant hypostome, which is attached to the exoskeleton.[5]

They are a large and long lasting group, with some of the candidates for the first trilobites being librostomes in the order ptychopariida; and all post-Devonian[b]trilobites being in the order proetida, who are librostomes.

Some librostomes may not even be within the group, with Whittington (2003) placing some genera (Hemibarrandia, Lakaspis, Peraspis and Symphysurina) of the asaphid family Nileidae in the order Corynexochida.[6]

  1. ^ Ontogeny, hypostome attachment and trilobite classification. RA Fortey, Palaeontology, 1990
  2. ^ Cite error: The named reference Gon was invoked but never defined (see the help page).
  3. ^ Bignon, Arnaud; Waisfield, Beatriz G.; Vaccari, Emilio; Chatterton, Brian D. E. (2020). "Reassessment of the Order Trinucleida (Trilobita)". Journal of Systematic Palaeontology. 18 (13): 1061–1077. Bibcode:2020JSPal..18.1061B. doi:10.1080/14772019.2020.1720324. S2CID 212995185.
  4. ^ "The Hypostome".
  5. ^ Whittington, H. B. "Reflections on the Classification of the Trilobita". University of Cambridge.
  6. ^ Whittington, Harry B. (2003). "The trilobite family Nileidae: morphology and classification". Palaeontology. 46 (4): 635–646. Bibcode:2003Palgy..46..635W. doi:10.1111/1475-4983.00313.


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