Overview

Comprehensive Description

Diversity

There are approximately 320 described species in Aplacophora. However, it is likely there are many other species that have not been described.

  • Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..
  • Scheltema, A. 2001. Aplacophora. Pp. 1-18 in A Wells, W Houston, eds. Zoological Catalogue of Australia, Vol. 17.2. Melbourne, Australia: CSIRO Publishing.
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Distribution

Geographic Range

Aplacophorans are found throughout the oceans over the world.

Biogeographic Regions: arctic ocean ; indian ocean; atlantic ocean ; pacific ocean ; mediterranean sea

  • Barnes, R. 1987. Invertebrate Zoology. Orlando, Florida: Dryden Press.
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Physical Description

Morphology

Sexual Dimorphism

Slight Sexual Dimorphism in epithelium surrounding the

gonoduct; ripe gonads are sometimes visible externally.

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Physical Description

Aplacophorans are small, cylindrical, worm-like, and usually less than 5 cm long, but can range from 1 mm to 30 cm. Like other mollusks, it has no outer shell, but the epidermis secretes calcareous spicules or scales which are embedded in dorsal mantle. These spicules give the aplacophorans a sheen. Chaetoderms have a scaly appearance. All aplacophorans have a simple mantle cavity.

The radula is not ribbon-like as in other mollusks, but is an expansion of the foregut epithelium. The teeth of the radula may be in simple plates in transverse rows, up to 50 rows with 24 teeth per row.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

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Ecology

Habitat

Exclusively marine, aplacophorans mainly burrow into the substrate in water more than 20 m deep, and may reach densities up to 4-5 per square meter. Aplacophorans in the sub-class Chaetodermomorpha are limited by a minimum salinity of 28-30%.

Habitat Regions: saltwater or marine

Aquatic Biomes: benthic

  • Jones, A., J. Baxter. 1987. Molluscs: Caudofoveata, Solenogastres, Polyplacophora and Scaphopoda. London: E. J. Brill and Dr. W. Backhuys.
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Trophic Strategy

Food Habits

Chaetoderms burrow and feed on microorganisms and detritus while neomenioids live with and feed on cnidarians.

Primary Diet: carnivore ; omnivore ; detritivore

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Associations

Ecosystem Roles

Neomenioids live with and feed on cnidarians but the effects on the ecosystem are unknown.

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Life History and Behavior

Behavior

Communication and Perception

Little is known about the perception of the Aplacophora. The animals have a simple nerve ring around the esophogus and poorly developed ganglia.

Perception Channels: tactile ; chemical

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Life Cycle

Development

Development involves metamorphosis from a trocophore larva.

Development - Life Cycle: metamorphosis

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Life Expectancy

Lifespan/Longevity

Little is known about aplacophoran lifespans.

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Reproduction

Aplacophorans may be monoecious or dioecious with single or paired gonads. All discharge gametes through gonopericardial ducts into the pericardial (heart) chamber. Gametes then pass through gametoducts to the mantle cavity where they are then released outside the body. Animals in the Chaetodermomorpha have external fertilization while those in Neomeniomorpha are internally fertilized, and sometimes even brooded.

Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); simultaneous hermaphrodite; sexual ; fertilization (External , Internal ); ovoviviparous ; oviparous

Members of the Neomeniomorpha sometimes brood the eggs. However, most species release the gametes without further parental care.

Parental Investment: pre-fertilization (Provisioning); pre-hatching/birth (Provisioning, Protecting)

  • Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..
  • Ponder, W., M. Shea, D. Beechey, R. McBain. 2000. "Aplacophora (the spicule worms)" (On-line). Shelled Marine Mollusks of Temperate Australia. Accessed February 07, 2005 at http://www.danceweb.com.au/marine/data/majgrps.htm#apla.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
                                        
Specimen Records:55Public Records:15
Specimens with Sequences:17Public Species:6
Specimens with Barcodes:17Public BINs:8
Species:12         
Species With Barcodes:6         
          
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Barcode data

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Locations of barcode samples

Collection Sites: world map showing specimen collection locations for Aplacophora

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