Geographic Range
This species is known only from Japan. It was first discovered and described from
the Ryukyu Archipelago: Kasari Bay on Amami Island and in Urazoko Bay on Ishigaki
Island.
- Biogeographic Regions
- pacific ocean
Habitat
This clam species has an extraordinary life style: it lives inside the esophagus of
a sea cucumber,
Holothuria pardalis
. These sea cucumbers are normally found in sand under boulders on coral-reef flats
within the intertidal zone. The clams have been found nowhere else, they seem to occur
only in this host species.
- Habitat Regions
- temperate
- saltwater or marine
Physical Description
Species in the genus
Entovalva
all have very distinct morphologies compared to other bivalve species, presumably
because of adaptations to an endosymbiotic life style. Their shells are small, thin
and completely enclosed in expanded mantle tissue. The gills are well developed and
extend outside the shell. In females, one part of the mantle cavity (the suprabranchial
chamber) is greatly enlarged and used to brood larvae. The foot is very well developed
and is usually bent to the left to attach the esophagus wall of the host. Middelfart
2011 is a link to a short video clip of a live Australian
Entovalva
.
- Other Physical Features
- ectothermic
- heterothermic
- bilateral symmetry
Development
The fertilized eggs are brooded in a suprabranchial chamber of the female until they
develop into D-shell veliger stage larvae. The larvae are then released and are thought
to pass through the host's intestine and out. To survive they must then be ingested
by a new host during the host's deposit-feeding activities.
- Development - Life Cycle
- metamorphosis
Reproduction
This species is a sequential protandric hermaphrodite. Clams are mostly found in pairs
inside one host: normally one big female individual and a small male. Interestingly,
the male is found attached to the female clam, not the host sea cucumber. In occasions
when only one individual is present in the host, that individual, if sexually mature,
is always a female.
- Mating System
- monogamous
- polyandrous
Entovalva lessonothuriae
are normally found in pairs: One female and one dwarf male. Very little is known
of reproductive modes. Fertilization is apparently internal, females retain their
fertilized embryos until the larvae reach the D-shell veliger stage. Clutch size,
breeding cycles, and age at reproduction are unknown.
- Key Reproductive Features
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- fertilization
- ovoviviparous
This species is a brooder: the female keeps fertilized eggs inside her suprabranchial
chamber until they develop into veliger larvae. Males provide no parental investment.
- Parental Investment
- female parental care
-
pre-hatching/birth
-
protecting
- female
-
protecting
Lifespan/Longevity
The life span of Entovalva lessonothuriae is currently unknown, but it probably lives for multiple years.
Behavior
Entovalva lessonothuriae
has a bilaterally flattened foot that bends to the left. This is thought to be an
adaptation for attachment to the host holothurian's esophagus. The bivalve has also
retained autonomous locomotion, respiration and feeding abilities, which is unusual
compared to other endosymbiotic taxa.
Communication and Perception
Detailed studies about communication and perception of
Entovalva lessonothuriae
have not been done so far. However it is documented that sensory organs such as papillae
on the mantle (found in related species) are almost lacking in
Entovalva lessonothuriae
. This could be a result of the species' endosymbiotic life style. It's very likely
that individuals communicate chemically, so that males and females can locate each
other within a host.
- Communication Channels
- chemical
- Perception Channels
- chemical
Food Habits
The well-developed ctenidia (“gills”) suggest that
Entovalva lessonothuriae
is still a filter feeder, even though it lives within the digestive tract of its
host holothurian.
- Primary Diet
- planktivore
- Animal Foods
- zooplankton
- Other Foods
- detritus
- Foraging Behavior
- filter-feeding
Predation
Specific predators on Entovalva lessonothuriae are unknown. Its endosymbiotic life style probably protects it from many predators, though also makes it vulnerable to predators that attack its host.
Ecosystem Roles
In Kato (1998)'s study, 19%~33% of the holothurian hosts examined harbored
Entovalva lessonothuriae
and did not contain any other symbionts. This suggests that
Entovalva lessonothuriae
might discourage competitors, but no other evidence of this has been discovered.
It is not known whether
Entovalva lessonothuriae
has any effect on the host's nutrition. The size of the bivalve was very weakly correlated
with host biomass. So far,
Entovalva lessonothuriae
has only been found from one host species, but only one other holothurian species
in its range,
Patinapta ooplax
, is known to have been examined.
Economic Importance for Humans: Positive
Entovalva lessonothuriae has no known economic value for humans.
Economic Importance for Humans: Negative
There are no known adverse effects of Entovalva lessonothuriae on humans.
Conservation Status
The population size of this species is unknown, and it has not been given any special legal protections.
Additional Links
Contributors
Jingchun Li (author), Special Projects, George Hammond (editor), Animal Diversity Web Staff.
- Pacific Ocean
-
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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).
- saltwater or marine
-
mainly lives in oceans, seas, or other bodies of salt water.
- 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.
- coastal
-
the nearshore aquatic habitats near a coast, or shoreline.
- ectothermic
-
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
- 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.
- 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.
- 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.
- monogamous
-
Having one mate at a time.
- polyandrous
-
Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous).
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- fertilization
-
union of egg and spermatozoan
- internal fertilization
-
fertilization takes place within the female's body
- 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.
- female parental care
-
parental care is carried out by females
- motile
-
having the capacity to move from one place to another.
- sedentary
-
remains in the same area
- chemical
-
uses smells or other chemicals to communicate
- chemical
-
uses smells or other chemicals to communicate
- zooplankton
-
animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)
- detritus
-
particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).
- 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.
- planktivore
-
an animal that mainly eats plankton
References
Kato, M. 1998. Morphological and ecological adaptations in montacutid bivalves endo- and ecto-symbiotic with holothurians. Canadian Journal of Zoology , 76: 1403–1410.
Middelfart, P., M. Craig. 2004. Description of Austrodevonia sharnae n. gen., n. sp. (Galeommatidae: Bivalvia), an ectocommensal of Taeniogyrus australianus (Stimpson, 1855) (Synaptidae: Holothur- oidea). Molluscan Research , 24: 211–219.
Middelfart, P. 2011. "Bizarre clam: Entovalva sp." (On-line). Youtube. Accessed July 31, 2011 at http://www.youtube.com/watch?v=5hPGUozETN0 .