title for learn-about sections for chitons in A SNAIL'S ODYSSEY
  Predators & defenses
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photograph of gumgoot chiton Cryptochiton stelleri rolling into a ballInvertebrate predators of chitons are chiefly sea stars and possibly snails. Vertebrate predators include birds, fishes, and sea otters.  Defenses of strong attachment, heavy overlapping shell plates, and ability of many species to curl into a ball appear to be effective against most other potential invertebrate and vertebrate predators. Few studies have been done specifically on predators of west-coast chitons.

 

 

 

 

 

A gumboot chiton Cryptochiton stelleri rolling
up in response to perceived danger 1X

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photograph of chiton Mopalia sp. preparatory to its curling into a ball taken from a video

CLICK HERE to see a video of a chiton Mopalia sp. curling into defensive posture.

NOTE the video replays automatically

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At first glance, the hairy muscular girdle of Mopalia muscosa would seem to be defensive, and this is supported by the observation that touching the hairs can lead to clamping down or, if they are bent with the fingers, to an apparent excape locomotion away from the bend.  However, a careful study of their ultrastructure by researchers at the University of Washington, Seattle suggests that other sensory functions may possibly drawing showing fine detail of hair structure on the girdle of a chiton Mopalia muscosabe served.  Each hair originates from a specialised group of epithelial cells embedded in an homogenous chitinous cuticle, 0.1mm in thickness, that overlies the epidermis, and each is associated with conspicuous dendritic bundles (see drawing).  These nervous elements are intimately associated with numerous sensory cells at their bases, and each emerges as an axon leading presumably to the central nervous system.  The hair is comprised of an outer and inner cortex, and a central medulla.  Muscles fibers penetrate the epidermis and may be involved with contraction of the girdle.  The hairs themselves are chitinous and unbranched, are about 5mm in length, and are present in densities of about 5 . mm2.  Numerous spicules comprised of crystals of calcium carbonate and brown pigment granules are scattered throughout the cuticle (density 2500 . mm2).  Despite the discovery of various nerves associated with the hairs suggestive of a sensory function, they bear little resemblance to other epidermal sensory receptors found in the buccal cavity, pallial grooves, and other parts of chitons.  The authors photograph of hairy chiton Mopalia muscosa in a tidepoolare therefore uncertain of their exact function.  Considerable electron-micrographical detail is provided in the study.  Leise & Cloney 1982 Cell Tiss Res 223: 43.

 

 


Hairy chiton Mopalia muscosa crawls in
a tidepool 0.6X

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  Invertebrate predators
  Invertebrate predators, sea stars and snails, are considered in this section and VERTEBRATE predators in another section.
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Sea stars

 
Research study 1
 

photograph of ochre stars Pisaster ochraceus in a rocky gulley
Three major studies on feeding of ochre stars Pisaster ochraceus in California and northern Washington, collectively involving over 3200 individual feeding observations, indicate that 6 or so species of chitons represent about 5% of the total number of prey items selected.  Feder 1959 Ecology 40: 721; Paine 1966 Am Nat 100: 65; Mauzey et al. 1968 Ecology 49: 603.

 

 

 

 

 

 

 

 

 

Distributions of ochre stars Pisaster ochraceus on
west-coast shores overlap with many species of chitons

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Research study 2
 

photograph of chiton Cyanoplax hartwegii courtesy Jim Watanabe, Hopkins Marine Station, Pacific Grove, Californiaphotograph of the brown fucales alga Silvetia compressa courtesy Jim Watanabe, Stanford University, CaliforniaOchre stars Pisaster ochraceus are potential predators of chitons Cyanoplax hartwegii in Pacific Grove, California. The potential protection of algal cover for Cyanoplax against Pisaster ochraceus predation is examined in an experiment in which several Pisaster are placed on a rock half covered with the green alga Silvetia compressa, and bearing a population of Cyanoplax. Over a single tidal cycle 10 chitons are eaten from the bare side and only 2 from the Silvetia-covered side.  Besides confirming that Pisaster will prey on Cyanoplax, the study shows that significant protection is offered the chiton by the covering of Silvetia.  Whether the alga interferes with normal crawling of the sea star, or offers some kind of chemical camouflage to the chiton, is not known.  DeBevoise 1975 Veliger 18(Suppl): 47. Photographs courtesy Jim Watanabe, Stanford University, California and calphotos.

NOTE the rock is 1.5 m2 in area, sits on sand, and extends about 1m above MLLW. 5d prior to addition of sea stars, the number of chitons is increased from 25 to 55, with the population stabilising to 45 on the day of the experiment.  The algal cover is then completely removed from half of the rock and, 30min prior to the incoming tide, 4 Pisaster are added to each side.  Any sea stars that fall off, or crawl off, over the subsequent high-tide cycle are replaced

 
Research study 3
 

photograph of chitons Tonicella lineataAlthough sea-star predation on lined chitons Tonicella lineata is commonly reported, a study in Pacific Grove, California shows that they are not eaten in the field by several common sea-star species, including Pisaster ochraceus, P. giganteus, and Patiria miniata, nor are they eaten to any significant extent by sea stars in the laboratory.  Some or all of the sea stars involved in the experiment, however, would later eat other species of chitons.  The author proposes that a chemical repellant and/or some kind of tactile inhibitor may be involved.  If a Tonicella is attached upside-down to a piece of glass, then presented to a sea star, it is most often eaten, suggesting that the dorsal surface may be the site of the protection.  The author notes that this is the first information on predation on T. lineata in California waters.  Seiff 1975 Veliger (Suppl.) 18: 54.

NOTE for example, of 92 Tonicella presented to P. giganteus, Orthasterias koehleri, and Leptasterias sp., none is eaten, and only 3 Tonicella are eaten by P. brevispinus


4 chitonsTonicella lineata and one black turban shell
Chlorostoma funebralis
in a coralline-alga area 0.5X

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Snails

 
Research study 1
 

photograph of gumboot chiton Cryptochiton stelleri courtesy Dave Cowles, Walla Walla University, WashingtonGastropods that prey on chitons are not common, but observations at Point Delgado in northern California indicate that the whelk Ocinebrina (Ocinebra) lurida will attack and eat gumboot chitons Cryptochiton stelleri.  Talmadge 1975 Veliger 17: 414. Photographs courtesy Dave Cowles, Walla Walla University, Washington rosario.wallawalla.edu.

 


Ventral surface of gumboot chiton
Cryptochiton stelleri
with head on Left

 
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