The Saddle tree oyster or Leaf oyster is a bivalve belonging to the family Pteriidae, otherwise known as Feather oysters. Pteriidae are medium-sized large saltwater clams. The range of I. ephippium spread throughout the Indo-Pacific. The species measures between 80 and 140 millimeters and has a white to greyish shell. It is distinguishable from bivalves of this family by its rounded outline, in contrast to the irregular outline of other species of the family. It has several transverse grooves in its hinge and attaches to mangrove roots and rocks with its massive byssal threads – a bundle of filaments used by many bivalves to be attach to a solid surface.
The saddle tree oyster is found in interdigital habitats, most commonly in mangrove habitats and ecosystems, up to a maximum depth of 10 meters. It can occasionally be seen growing on rocks or sea walls in sheltered areas near river mouths and other freshwater inflows. Like most other bivalves, the saddle tree oyster is a filter feeder and as such plays an important role in keeping seawater clean. It is often found in large groups.
Although the population of I. ephippium is not currently threatened due to its population size and range, threats persist due to habitat loss.
Isognomon oysters use their byssus to completely cement themselves to the roots of mangrove trees, corals, and other substrates. A clear preference for mangrove tree is observed, hence the common name in English ‘Tree oysters’.