Merostomata

Merostomata
Reconstruction of Eurypterus (Eurypterida)
Five views of Limulus polyphemus (Xiphosura)
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Class:	Merostomata Woodward, 1866
Orders
Order Eurypterida Order Xiphosura

Merostomata is the name given to a grouping of the extinct Eurypterida (sea scorpions) and the Xiphosura (horseshoe crabs). The term was originally used by James Dwight Dana to refer to Xiphosura only, but was emended by Henry Woodward to cover both groups.

Etymology

The name "Merostomata" derives from the Greek roots μηρός (meros, "thigh") and στόμα (stoma, "mouth"), in reference to the animals possession of appendages which are mouthparts at their proximal end, but swimming legs at their distal end.^[1]

History

The scientific consensus at the beginning of the twentieth century was that these two marine groups were closely related, and only more distantly related to the terrestrial Arachnida.^[2] More recent analyses suggest that the grouping Merostomata is not monophyletic, with Xiphosura being basal to a clade comprising Eurypterida and Arachnida.^[3] It is estimated that the Xiphosura diverged from the Arachnida 480 million years ago.^[4]

The shared features of the two groups traditionally grouped in the Merostomata are now thought to be retentions of primitive conditions (symplesiomorphies), and thus it has been recommended that the name Merostomata be abandoned.^[3]

References

1. ^ A monograph of the British Fossil Crustacea, belonging to the Order Merostomata. Part 1. Pterygotus Anglicus, Agassiz. Pages 1–44. Plates i.–ix. By Henry Woodward, F.G.S., F.Z.S., of the British Museum. "Literary Notices". The Intellectual Observer: review of natural history, microscopic research, and recreative science 11: 233–234. 1867. http://books.google.co.uk/books?id=BMgWAQAAIAAJ&pg=PA234. 
2. ^ J. A. Dunlop & P. A. Selden (1998). "The early history and phylogeny of the chelicerates". In Richard A. Fortey & Richard H. Thomas. Arthropod relationships. Volume 55 of Systematics Association Series. Springer Verlag. pp. 221–236. ISBN 9780412754203. http://books.google.co.uk/books?id=Pj-q9eHyIx0C&pg=PA221.  Also available as PDF
3. ^ ^{a b} Colin Tudge (2002). "Spiders, scorpions, mites, eurypterids, horseshoe crabs, and sea spiders. Subphylum Chelicerata and Subphylum Pycnogonida". The variety of life: a survey and a celebration of all the creatures that have ever lived. Oxford University Press. pp. 309–326. ISBN 9780198604266. http://books.google.co.uk/books?id=YW-2gnuU0L0C&pg=PA312. 
4. ^ Davide Pisani, Laura L. Poling, Maureen Lyons-Weiler & S. Blair Hedges (2004). "The colonization of land by animals: molecular phylogeny and divergence times among arthropods". BMC Biology 2: 1. doi:10.1186/1741-7007-2-1. PMC 333434. PMID 14731304. http://www.biomedcentral.com/1741-7007/2/1. 

External links

Media related to Merostomata at Wikimedia Commons