''Enigmonia'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of saltwater clams, a

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Anomiidae, the jingle shells. ''Enigmonia aenigmatica'', the mangrove jingle shell clam, is the only species in this

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

genus. It is found living on mangroves in the Indo-Pacific Ocean.

Description

The mangrove jingle shell clam can grow to a length of about . The shell is thin and delicate. Although this species is a bivalve, only the upper valve is normally visible, and that valve is elongated or oval with a low dome, and thus the general appearance which is like that of a

limpet Limpets are a group of aquatic snails that exhibit a conical shell shape (patelliform) and a strong, muscular foot. Limpets are members of the class Gastropoda, but are polyphyletic, meaning the various groups called "limpets" descended indep ...

. The umbone of the shell is off centre, near the dorsal margin of the shell. A few fine ridges radiate from the umbone and there is a sculpting of concentric growth rings. The lower valve has a hole or notch in it through which

byssus A byssus () is a bundle of filaments secreted by many species of bivalve mollusc that function to attach the mollusc to a solid surface. Species from several families of clams have a byssus, including pen shells (Pinnidae), true mussels (Mytilid ...

threads pass which attach it to a hard surface, usually a branch, leaf or aerial root of a mangrove tree.Mangrove jingle shell: ''Enigmonia aenigmatica''
Wildsingapore. Retrieved 2012-04-23. The lower valve is curved so as to adhere closely to the surface on which it rests. Unlike most other bivalves, but like others in the genus, it has a single adductor muscle holding the two valves together. The

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

of the mangrove jingle shell depends on the nature of the substrate on which it has settled. When it is a juvenile the animal can and does move around, but later it becomes

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

. If it is on a mangrove leaf, the shell becomes flattened and more or less oval. However, on hard surfaces such as the branches of '' Avicennia'' and the aerial prop roots of '' Rhizophora'', it is more domed and the animal orientates itself with regard to the water current and the axis of the wood. The mangrove jingle shell has two distinct colour varieties, one cream, usually found on the underside of mangrove leaves, and the other brownish purple and found on mangrove bark. At first it was thought that these represented two different species or two morphs occupying different

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

s. However, in an experiment, cream-coloured shells were transplanted from leaves onto mangrove branches and began to change colour over the course of a few weeks. They became purplish-brown at the margins where new shell material was laid down. Other cream-coloured shells were left as controls on leaves and they showed no colour changes. The researchers concluded that the colour of the shell was not genetically controlled but was determined by the nature of the substrate on which the animal lived.

Distribution

The mangrove jingle shell is found on coasts in the tropical Indo-Pacific Ocean, where it is a characteristic member of the mangrove community. The range extends from Malaya and the Philippines to the northern coast of Australia.

Biology

The mangrove jingle shell is a

filter feeder Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...

. Like bivalves living in the

intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...

on sandy beaches, this species feeds while the tide is in and it is submerged; otherwise it gathers food particles from splashes of sea water.

References

{{Taxonbar, from1=Q5378952, from2=Q18594917 Anomiidae Bivalve genera Monotypic mollusc genera Bivalves of Asia Molluscs of Oceania Mangrove fauna Fauna of Southeast Asia Invertebrates of Borneo Fauna of India Fauna of Indonesia Fauna of Malaysia Molluscs of New Guinea