| Pteriomorphia | |
|---|---|
 | |
| A live individual ofArgopecten irradians, family Pectinidae | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Bivalvia |
| Subclass: | Pteriomorphia Beurlen, 1944 |
ThePteriomorphia comprise asubclass of saltwater clams,marinebivalvemolluscs.[1] It contains several major orders, including theArcida,Ostreida,Pectinida,Limida,Mytilida, andPteriida. It also contains someextinct and probablybasalfamilies, such as theEvyanidae,Colpomyidae,Bakevelliidae,Cassianellidae, andPlicatostylidae.
This subclass of molluscs haslamellibranchgills, and isepibenthic. Some attach to thesubstrate using abyssus. The foot is reduced. Themantle margins are not fused. Gills are usually large and assist in feeding. This group includes the well knownmussels,scallops,pen shells, andoysters.[2] It also includes the only members of the classbivalvia to haverudimentary eyes.
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 theirsiphon, 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 inPectinidae exhibit a reduction in functionality as habitat depth increases, ending in the complete absence of eyes in deep sea species.[6]
Thecladogram 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 |
| ||||||||||||||||||||||||||||||||||||||||||
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 theWorld Register of Marine Species[9]
Subclass: Pteriomorphia
(Ark shells and bittersweet shells)
(True oysters and their allies)
(Scallops and their allies)
(File shells and their allies)
(Saltwater mussels)
(Winged oysters and their allies)
