Thecostraca

Thecostraca Temporal range: Carboniferous–Recent PreꞒ Ꞓ O S D C P T J K Pg N
A barnacle of the family Balanidae, Mission Beach, Queensland, Australia, 2001.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Superclass:	Multicrustacea
Class:	Thecostraca Gruvel, 1905
Subclasses
Facetotecta Ascothoracida Cirripedia

Thecostraca is a class of marine invertebrates containing over 2,200 described species.^[1] Many species have planktonic larvae which become sessile or parasitic as adults.

The most prevalent subgroup are the barnacles (subclass Cirripedia), constituting a little over 2,100 known species.^[1]

The subgroup Facetotecta contains a single genus, Hansenocaris, known only from the tiny planktonic nauplii called "y-larvae". These larvae have no known adult form, though it is suspected that they are parasites, and their affinity is uncertain. Some researchers believe that they may be larval tantulocaridans. No larval tantulocaridans are currently known.^[2]

The group Ascothoracida contains about 110 species, all parasites of coelenterates and echinoderms.^[1][3]

The nauplius larvae (sometimes absent) can be both lecithotrophic (non-feeding) and planktotrophic (feeding), and is followed by a larval stage called the cyprid, which is always lecithotrophic. The cypridoid larvae are referred to as the y-cyprid in the Facetotecta, the a-cyprid in the Ascothoracida, and the c-cyprid, or just cyprid, in the Cirripedia.^[4][5]

Classification

This article follows Chan et al. (2021) and the World Register of Marine Species in placing Thecostraca as a class of Crustacea and in the following classification of thecostracans down to the level of orders. Previously, Thecostraca was considered a subclass of Maxillopoda.^[2] Significant changes in the organization of Cirripedia's orders, families, and genera were introduced in 2021 by Chan et al. and accepted by the World Register of Marine Species.^[1][6]

Class Thecostraca Gruvel, 1905

• Subclass Ascothoracida Lacaze-Duthiers, 1880
  • Order Laurida Grygier, 1987
  • Order Dendrogastrida Grygier, 1987
• Subclass Facetotecta Grygier, 1985
• Subclass Cirripedia Burmeister, 1834
  • Infraclass Acrothoracica Gruvel, 1905
    • Order Lithoglyptida Kolbasov, Newman & Hoeg, 2009
    • Order Cryptophialida Kolbasov, Newman & Hoeg, 2009
  • Infraclass Rhizocephala Müller, 1862
  • Infraclass Thoracica Darwin, 1854
    • Superorder Phosphatothoracica Gale, 2019 (paraphyletic)
      • Order Eolepadomorpha Chan et al., 2021 †
      • Order Iblomorpha Buckeridge & Newman, 2006
    • Superorder Thoracicalcarea Gale, 2015
      • Order Calanticomorpha Chan et al., 2021
      • Order Brachylepadomorpha Withers, 1923 †
      • Order Archaeolepadomorpha Chan et al., 2021 †
      • Order Verrucomorpha Pilsbry, 1916
      • Order Scalpellomorpha Buckeridge & Newman, 2006
      • Order Pollicipedomorpha Chan et al., 2021
      • Order Balanomorpha Pilsbry, 1916

Phylogeny

The following cladogram depicts the internal relationships of the Thecostraca as of 2021.^[1][7]

Thecostraca	Facetotecta Ascothoracida Laurida Dendrogastrida Cirripedia Acrothoracica Cryptophialida Lithoglyptida Thoracica Iblomorpha Eolepadomorpha† Thoracicalcarea Archaeolepadomorpha † Pollicipedomorpha Calanticomorpha Scalpellomorpha Brachylepadomorpha† Sessilia Verrucomorpha Balanomorpha Rhizocephala	"Phosphatothoracica"

References

1. Chan, Benny K. K.; Dreyer, Niklas; Gale, Andy S.; Glenner, Henrik; et al. (2021). "The evolutionary diversity of barnacles, with an updated classification of fossil and living forms". Zoological Journal of the Linnean Society. 193 (3): 789–846. doi:10.1093/zoolinnean/zlaa160. hdl:11250/2990967.
2. Joel W. Martin & George E. Davis (2001). An Updated Classification of the Recent Crustacea (PDF). Natural History Museum of Los Angeles County. pp. 132 pp.
3. Paul Schmid-Hempel (2011). "The diversity and natural history of parasites". Evolutionary Parasitology: the Integrated Study of Infections, Immunology, Ecology, and Genetics. Oxford University Press. pp. 18–51. ISBN 978-0-19-922949-9.
4. Glenner, H.; Høeg, J. T.; Grygier, M. J.; Fujita, Y. (2008). "Induced metamorphosis in crustacean y-larvae: Towards a solution to a 100-year-old riddle". BMC Biology. 6: 21. doi:10.1186/1741-7007-6-21. PMC 2412843. PMID 18492233.
5. Martin, Joel W.; Olesen, Jørgen; Høeg, Jens T. (July 2014). Atlas of Crustacean Larvae. JHU Press. ISBN 978-1-4214-1198-9.
6. "World Register of Marine Species, class Thecostraca". Retrieved 2021-08-22.
7. Pérez-Losada, Marcos; T. Høeg, Jens; A. Crandall, Keith (September 2021). "Deep Phylogeny and Character Evolution in Thecostraca (Crustacea: Maxillopoda)". Integrative and Comparative Biology. 52 (3): 430–442. doi:10.1093/icb/ics051. PMID 22532607.

External links

• Data related to Thecostraca at Wikispecies