''Enigmonia'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of saltwater clams, a marine

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Anomiidae Anomiidae is a family of saltwater clams, marine bivalve molluscs related to scallops and oysters, and known as anomiids. It contains seven genera. The family is known by several common names, including jingle shells, mermaid's toenails, and ...

, 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 "unisp ...

genus. It is found living on

mangrove A mangrove is a shrub or tree that grows mainly in coastal saline water, saline or brackish water. Mangroves grow in an equatorial climate, typically along coastlines and tidal rivers. They have particular adaptations to take in extra oxygen a ...

s 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 with a conical gastropod shell, shell shape (patelliform) and a strong, muscular foot. This general category of conical shell is known as "patelliform" (dish-shaped). Existing within the class Gastropoda, ...

. 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 (Mytili ...

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 ''Avicennia'' is a genus of flowering plants currently placed in the bear's breeches family, Acanthaceae. It contains mangrove trees, which occur in the intertidal zones of estuarine areas and are characterized by its "pencil roots", which ar ...

'' and the aerial prop roots of ''

Rhizophora ''Rhizophora'' is a genus of tropical mangrove trees, sometimes collectively called true mangroves. The most notable species is the red mangrove ('' Rhizophora mangle'') but some other species and a few natural hybrids are known. ''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, habitat refers to the array of resources, 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 manifestation of its ...

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 Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

on which the animal lived.

Distribution

The mangrove jingle shell is found on coasts in the tropical

Indo-Pacific Ocean The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the s ...

, 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 aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a s ...

. Like bivalves living in the

intertidal zone The intertidal zone or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various ...

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