Ephippodonta lunata

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Geographic Range

Ephippodonta lunata is endemic to the southern coast of Australia. The type locality is Long Beach, South Australia. It is possible that the distribution of this species ranges from Western Australia to Victoria. (Cotton, 1938; Middelfart, 2005)

Habitat

This species has a non-obligate commensal relationship with the slow shrimp Axius plectorhynchus. The shrimp burrows in the sediment, forming a usually horizontal tube with diameters from 0.5~1.5 inches (1-3 cm); and the clam just locates in the burrow without apparently obstructing the shrimp’s movements. However, Ephippodonta lunata can also be found crawling in rock crevices in the shallow intertidal and subtidal. (Cotton, 1938)

Physical Description

Ephippodonta lunata is one of the peculiar clams with gaping valves that belong to the superfamily Galeommatoidea. When alive, the two semicircular valves are held fully open at 180°C from each other; together they form a moon-like shape, hence the common name of this animal - moon cockle. The shells are up to 10 mm long and 4.5 mm wide. The shell surface has rough sculpturing composed of different types of pustules, ranging from minute rounded granulae about 10 μm in diameter to pedunculate articulating pustules around 300 μm long. The pustules may easily fall off when dried. The degree of pustule development could be different for different specimens. Also, some shells appear to have radial color patterns on them and some do not. The above characters make the shells polymorphic among individuals. (Cotton, 1938; Middelfart, 2005)

In large individuals, the mantle extends and reflects to cover the shells, it is non-retractable but generally does not cover the prodissoconch. Small individuals don’t have mantle reflections. The mantle edge of the animal is thickened and posses pustules. There also present four anterior as well as six posterior tentacles. The mantle forms an anterior cowl and a posterior exhalant siphon. The foot is large and can protrude through the cowl. Middelfart 2011 is a link to a short video showing the bizzare appearance and movement of this clam. (Middelfart, 2005; Middelfart, 2011)

  • Range length
    10 (high) mm
    0.39 (high) in

Development

The fertilized eggs are brooded in mantle cavities of females, then released as veliger larvae. No detailed studies have been done on the development of this species. However, studies on species from the same superfamily show that early cleavage to larval release may take 12-29 days, or even up to 2 months. the veligers feed on the plankton and metamorphosis into juveniles. (Jespersen and Lützen, 2006)

Reproduction

Species in the superfamily Galeommatoidea either have separate sexes or are protandric or simultaneous hermaphrodites. Specific information about the reproductive mode of Ephippodonta lunata is currently unknown. However studies of other species in the genus Ephippodonta have revealed the existence of dwarf males (miniature mature males that live inside adult female individuals). (Morton, 1976; Ponder, 1998)

Reproductive behaviors of this species has not been closely observed or documented so far. Based on its commensal living style, it is possible that the males may exhibit bulk sperm transfer/storage mechanisms such as dimorphic sperm, spermatophores, seminal receptacles or dwarf males, etc. (Jespersen and Lützen, 2006)

We have no information on parental investment in this species. However, all species in the Galeommatoidea studied to-date brood their young. (Jespersen and Lützen, 2006; Ponder, 1998)

Lifespan/Longevity

The life span of Ephippodonta lunata is currently unknown, but most galeommatoidean species live for multiple years.

Behavior

When in the shrimp burrows, Ephippodonta lunata forms a slight depression in the mud lining on the wall and compresses itself, perhaps to stay out of the way of the resident shrimp. (Cotton, 1938)

Communication and Perception

Detailed studies on the communication and perception of Ephippodontamorpha hirsutus have not been done so far. But it is possible that this species uses chemical cues to communicate with conspecifics and to find the host shrimp.

Food Habits

Ephippodonta lunata is probably a suspension feeder.

Predation

Known predators of Ephippodonta lunata have not been documented so far. However the commensal bivalve could potentially be predated by a spectrum of benthic predators if they can get access to it.

Ecosystem Roles

Ephippodonta lunata is not the only commensal in the shrimp burrow. The burrow of the shrimp host Axius plectorhynchus may harbor other commensals as well, including a sponge and other galeommatoidean bivalves. (Cotton, 1938)

Species Used as Host
  • Axius plectorhynchus

Economic Importance for Humans: Positive

There are no known positive effects of Ephippodonta lunata on humans.

Economic Importance for Humans: Negative

There are no known adverse effects of Ephippodonta lunata on humans.

Conservation Status

Very little is known about the population status of this species. It does not receive any special conservation effort at the time of this writing.

Contributors

Jingchun Li (author), Special Projects, George Hammond (editor), Animal Diversity Web Staff.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

detritus

particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

filter-feeding

a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

native range

the area in which the animal is naturally found, the region in which it is endemic.

ovoviviparous

reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

phytoplankton

photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)

planktivore

an animal that mainly eats plankton

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

Cotton, B. 1938. Ephippodonta-South Australia's most peculiar bivalve shell. Victorian Naturalist, 58–61.

Jespersen, Å., J. Lützen. 2006. Reproduction and sperm structure in Galeommatidae (Bivalvia, Galeommatoidea). Zoomorphology, 125/3: 157-173.

Middelfart, P. 2011. "Ephippodonta lunata (Tate, 1887)" (On-line). Youtube. Accessed July 30, 2011 at http://www.youtube.com/watch?v=TOSLlDZONUQ.

Middelfart, P. 2005. Review of Ephippodonta sensu lato (Galeommatidae: Bivalvia), with descriptions of new related genera and species from Australia. Molluscan Research, 25/3: 129-144.

Morton, B. 1976. Secondary brooding of temporary dwarf males in Ephippodonta (Ephippodontina) oedipus sp. nov. (Bivalvia: Leptonacea). Journal of Conchology, 29: 31-39.

Ponder, W. 1998. Superfamily Galeommatoidea. Pp. 316–318 in R de Keyzer, P Beesley, G Ross, eds. Mollusca : The Southern Synthesis. Melbourne: CSIRO Publishing.