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Chlamydoconcha orcutti

By Jingchun Li

Geographic Range

Chlamydoconcha orcutti is found along the west coast of North America (Eastern Pacific), from northern California (Shell Beach, Sonoma Co. (38.4°N)), south to Punta San Pablo, Baja California Sur (27.2°N). (Carlton, 1979; Coan, et al., 2000)

Habitat

This species occurs near shore, from the intertidal zone to 40m depth. It was normally found under rocks, crawling or anchored by byssal threads. Sometimes it can also be found within kelp holdfasts. (Carlton, 1979; Coan, et al., 2000)

  • Range depth
    0 to 40 m
    0.00 to 131.23 ft

Physical Description

Chlamydoconcha orcutti is one of the most peculiar looking clams, commonly known as the “naked clam”. In large adults (see reproduction section for more information about dwarf males) the shells are highly reduced and completely embedded in the enlarged, translucent white mantle. The shells grow mostly anteriorly and have little posterior growth, resulting in an elongated, lanceolate shape. The prodissoconch (rudimentary larval shell) is often clearly demarcated. (Morton, 1981)

The mantle is greatly thickened and fused, forming an “envelope” that encloses the shells. The anterior mantle opening acts as the inhalant pathway for the animal and a posterior siphon forms the exhalent opening. The dorsal-lateral surface of the mantle exhibits many white papillae that are retractable into pits. The papillae have various spherical inclusions that act as secretory tubules. Those papillae may have a chemical defense function protecting the animal from its predators. A group of unique papillae also exists behind the anterior mantle opening, forming an anemone-like disc structure known as the pheromone organ. (Morton, 1981; Rouse, 2011)

Chlamydoconcha orcutti has a very large and muscular foot that enables it to crawl around very actively; together with the thickened mantle, they give this animal an appearance of a sea slug rather than a clam. Rouse, 2011 is a video of two live specimens in captivity– have a look for yourself! (Rouse, 2011)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    4 to 13.5 mm
    0.16 to 0.53 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

Chlamydoconcha orcutti has two very different adult body forms. Large individuals as described above are typically hermaphroditic. They possess both female and male reproductive organs and both can be functional, although sometimes one sex may be much more developed than the other. However, tiny sexually mature “dwarf” males are often present. They are significantly smaller than the large hermaphroditic adults and cannot live by themselves. Dwarf males are typically found inside mantle cavities of large individuals, attached by byssal threads. Their shells have prominent prodissoconchs and are also covered with extended mantle tissue. (Morton, 1981)

Chlamydoconcha orcutti is a protandric sequential hermaphrodite. In the presence of large conspecifics, planktonic larva may metamorphose directly into dwarf male forms, but this is not a permanent stage. If environmental conditions allow, dwarf males can subsequently develop into large hermaphroditic body form. The evollution of dwarf male morphs may represent adaptation to small population sizes and isolated distributions. (Morton, 1981; Ó Foighil, 1985)

Dwarf males or hermaphroditic large adults release spermatozoa that are taken up by the incurrent siphon of the egg-producing partner. The eggs are fertilized and incubated in the suprabranchial chamber of the female/hermaphrodite. (Morton, 1981)

Chlamydoconcha orcutti are brooders, i.e., fertilized eggs and developing embryos are protected inside the mantle cavity until they are released as free-living planktonic larvae. (Morton, 1981)

  • Parental Investment
  • pre-hatching/birth
    • protecting
      • female

Lifespan/Longevity

Most Chlamydoconcha orcutti adult individuals were observed in fall and winter (August to January, occasionally in April), with population peaks about October. Lifespan of this species is not determined, but the clam could probably live for several years. (Carlton, 1979; Morton, 1981)

Behavior

Chlamydoconcha orcutti normally attaches to the bottom of rocks, however when detached, it can crawl and move actively with it's large, muscular foot. (Morton, 1981)

Communication and Perception

The pheromone organ described above is suggested to be secretory and might be used to attract and guide males. (Bernard, 1897; Morton, 1981)

Food Habits

Chlamydoconcha orcutti is a suspension feeder, it gathers food particles from the water column by passing current through its ctenidia (“gills”). Filtered material travels within food grooves to the mouth. (Morton, 1981)

Predation

Specific predators of Chlamydoconcha orcutti are not identified, but it could be potentially be predated by a spectrum of benthic predators if they can have access to it. Chlamydoconcha orcutti normally hides under rocks; papillae on the mantle of the clam are likely to be chemical defensive organs that protect the animal from its predators. (Morton, 1981)

Ecosystem Roles

Very little is known about the ecology of this species, or its ecological relationships with other species.

Economic Importance for Humans: Positive

There are no known positive effects of Chlamydoconcha orcutti on humans.

Economic Importance for Humans: Negative

There are no known adverse effects of Chlamydoconcha orcutti on humans.

Conservation Status

Very little is known about the population status of this species. It does not receive any special legal protection.

Contributors

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

Glossary

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.

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

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

planktivore

an animal that mainly eats plankton

protandrous

condition of hermaphroditic animals (and plants) in which the male organs and their products appear before the female organs and their products

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

Bernard, F. 1897. Note préliminaire sur Chlamydoconcha Orcutti Dall, Lamellibranche à coquille interne. Bulletin du Muséum d'Histoire Naturelle, 3: 65-67.

Carlton, J. 1979. Chlamydoconcha orcutti Dall: review and distribution of a little-known bivalve. Veliger, 21: 375-378.

Coan, E., P. Valentich-Scott, F. Bernard. 2000. Bivalve Seashells of Western North America. Santa Barbara: Santa Barbara Musuem.

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

Morton, B. 1981. The biology and functional morphology of Chlamydoconcha orcutti with a discussion on the taxonomic status of the Chlamydoconchacea (Mollusca: Bivalvia). Journal of Zoology, London, 195: 81–121.

Rouse, G. 2011. "Chlamydoconcha" (On-line). Accessed August 19, 2011 at http://www.youtube.com/watch?v=Kr7m_OSzwV8.

Ó Foighil, D. 1985. Form, function and origin of temporary dwarf males in Pseudopythina rugifera (Carpenter, 1864) (Bivalvia: Galeommatacea). Veliger, 27: 245–252.

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