Pteriomorphia

The Pteriomorphia comprise a subclass of saltwater clams, marine bivalve molluscs.[1] It contains several major orders, including the Arcida, Ostreida, Pectinida, Limida, Mytilida, and Pteriida. It also contains some extinct and probably basal families, such as the Evyanidae, Colpomyidae, Bakevelliidae, Cassianellidae, and Lithiotidae.

Pteriomorphia
A live individual of Argopecten irradians, family Pectinidae
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Subclass: Pteriomorphia
Beurlen, 1944

This subclass of molluscs has lamellibranch gills, and is epibenthic. Some attach to the substrate using a byssus. The foot is reduced. The mantle margins are not fused. Gills are usually large and assist in feeding. This group includes the well known mussels, scallops, pen shells, and oysters.[2] It also includes the only members of the class bivalvia to have rudimentary eyes.

Photoreceptors

Pteriomorphian bivalves possess five types of photoreceptors, each evolving independently and each associated with different clades within Pteriomorphia.[3] There are cap eyespots, pigmented cups, compound eyes, concave mirror eyes, and invaginated eyes, each having evolved independently.[3] The primary purpose of pteriomorphian eyes is to detect and respond to predators.[4] As such, pteriomorphia respond to the presence of a shadow by retracting their siphon, adduction, digging, or some combination of the three. Beyond this shadow response, however, pteriomorphia typically do not respond to other visual stimuli.[5]

Pteriomorphia have much higher rates of eye loss than eye gain and studying eye loss and gain can yield insights into the mechanisms behind convergent evolution and the evolution and regression of complex traits.[3] Eyes evolved exclusively in epifaunal lineages, and have been lost in some lineages that adopted infaunal and semi-infaunal lifestyles, suggesting a correlation between eye loss and adoption of infaunal or semi-infaunal lifestyles.[3] Additionally, eyes in Pectinidae exhibit a reduction in functionality as habitat depth increases, ending in the complete absence of eyes in deep sea species.[6]

Phylogeny

The cladogram is based on molecular phylogeny using mitochondrial (12S, 16S) and nuclear (18S, 28S, and H3) gene markers by Yaron Malkowsky and Annette Klussmann-Kolb in 2012.[7]

Pteriomorphia
(c. 247 mya) Pectinidae

Palliolinae (in part)

Palliolinae (in part) and Camptonectinae

Chlamydinae

(70 mya) Pecten

Flexopecten

(247 mya) Aequipecten

Limidae (file shells)

other Pteriomorphia (oysters, mussels)

2010 Taxonomy

In 2010 a new proposed classification system for the Bivalvia was published by Bieler, Carter & Coan revising the classification of the Bivalvia, including the subclass Pteriomorphia.[8] However, the following taxonomy represents the current accepted arrangement of this subclass according to the World Register of Marine Species[9]

Subclass: Pteriomorphia

Order: Arcida[10]

(Ark shells and bittersweet shells)

Order: Ostreida[11]

(True oysters and their allies)

Order: Pectinida[12]

(Scallops and their allies)

Order: Limida[13]

(File shells and their allies)

Order: Mytilida[14]

(Saltwater mussels)

Order: Pteriida[15]

(Winged oysters and their allies)

Fossil orders

References
  1. Pteriomorphia Beurlen, 1944. Retrieved through: World Register of Marine Species on 26 March 2009.
  2. Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. p. 430. ISBN 978-0-03-056747-6.
  3. Audino, Jorge Alves; Serb, Jean Marie; Rodriguez Marian, José Eduardo Amoroso (27 July 2020). "Hard to get, easy to lose: Evolution of mantle photoreceptor organs in bivalves (Bivalvia, Pteriomorphia)". Evolution. 74 (9): 2106–2120. doi:10.1111/evo.14050. PMID 32716056. S2CID 220796915.
  4. Serb, Jeanne M.; Eernisse, Douglas J. (2008-10-01). "Charting Evolution's Trajectory: Using Molluscan Eye Diversity to Understand Parallel and Convergent Evolution". Evolution: Education and Outreach. 1 (4): 439–447. doi:10.1007/s12052-008-0084-1. ISSN 1936-6434. S2CID 2881223.
  5. Morton, Brian (January 2001). "The Evolution of Eyes in Bivalvia". Oceanography and Marine Biology: An Annual Review: 165–205 – via ResearchGate.
  6. Malkowsky, Yaron; Götze, Marie-Carolin (10 December 2013). "Impact of habitat and life trait on character evolution of pallial eyes in Pectinidae (Mollusca: Bivalvia)". Organisms Diversity and Evolution. 14 – via ResearchGate.
  7. Malkowsky, Yaron; Klussmann-Kolb, Annette (May 2012). "Phylogeny and spatio-temporal distribution of European Pectinidae (Mollusca: Bivalvia)". Systematics and Biodiversity. 10 (2): 233–242. doi:10.1080/14772000.2012.676572. S2CID 84085349.
  8. Bieler, R., Carter, J.G. & Coan, E.V. (2010) Classification of Bivalve families. Pp. 113-133, in: Bouchet, P. & Rocroi, J.P. (2010), Nomenclator of Bivalve Families. Malacologia 52(2): 1-184
  9. Gofas, S. (2014). "Pteriomorphia". World Register of Marine Species. Retrieved 2014-08-19.
  10. Arcoida Stoliczka, 1871. Retrieved through: World Register of Marine Species on 3 February 2009.
  11. Ostreoida Ferussac, 1822. Retrieved through: World Register of Marine Species on 9 July 2010.
  12. Pectinoida Gray, 1854. Retrieved through: World Register of Marine Species on 9 July 2010.
  13. Limoida Moore, 1952. Retrieved through: World Register of Marine Species on 7 July 2010.
  14. Mytiloida Ferussac, 1822. Retrieved through: World Register of Marine Species on 9 July 2010.
  15. Pterioida Newell, 1965. Retrieved through: World Register of Marine Species on 9 July 2010.
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