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  Predators & defenses
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  Pedicellariae
 

Defenses of asteroids include pedicellariae, considered here, and SPINES & OSSICLES, TUBE-FEET ANCHORING, ESCAPE BY CRAWLING, RIGHTING RESPONSE, DISTASTEFUL CHEMICALS, MUCUS, AUTOTOMY, and CAMOUFLAGE, considered in other sections. 

   
  The photos below show pedicellaria disposition and other skin details on the arms of 2 species of sea stars:
 
photograph of skin detail in the sea star Orthasterias koehleri
End-on view of 4 arms of a sea star Orthasterias koehleri showing spines lining the ambulacral grooves, dermal papulae, pedicellaria clusters, and red ocelli (eyespots) at the tips of the arms. The pedicellariae are extended to the tips of the arm spines hiding them, and are mostly open 1X
photograph showing close view of a sunflower star's arm
Side view of the ambulacral area of an arm of Pycnopodia helianthoides showing spines lining the ambulacral groove, clusters of small pedicellariae around the arm spines, larger vice-like pedicellariae scattered about, and tube feet. Most of the pedicellariae are quiescent 2.5X
 
 
photograph of dermal branchiae of a sea star taken from a video

CLICK HERE to see a video of pedicellariae clusters around the spines of a sunflower star Pycnopodia helianthoides. The moving sacs are the dermal papulae, dermal branchiae, or skin gills.

NOTE  the video replays automatically

 
Research study 1
 

photo composite showing pedicellariae of an ochre star Pisaster ochraceusPedicellariae occur on the skin surfaces and are found mainly in a single Order of sea stars, the Forcipulatida.  Examples of west coast forcipulatids are

Evasterias troschelii
Leptasterias hexactis
Leptasterias aequalis
Orthasterias koehleri
Pisaster ochraceus
Pisaster brevispinus
Pycnopodia helianthoides
Stylasterias forreri

The small jaws are used in defense and, one species, in food acquisition (see Research Study 3 below).  Shown here is a so-called straight pedicellaria on the oral surface of an ochre star Pisaster ochraceus. By the appearance of the tube feet around the mouth, this individual may have just been pulled roughly off a prey, and the pedicellariae are responding to the disturbance. Most of the pedicellariae visible are open and ready to bite. Like other pedicellariae in asteroids, these straight ones are non-toxic, and rely on snapping and crushing to ward off predators, and to kill small settling organisms. Drawing adapted from Verrill 1909 Am Nat 43: 542.

NOTE lit. “small foot units” L.  More information on pedicellariae can be found elsewhere in the ODYSSEY: LEARN ABOUT SEA URCHINS: DEFENSE: PEDICELLARIAE

 
 
photograph of biting pedicellariae in a sea star, possibly Pycnopodia helianthoides

CLICK HERE to see a video of biting activity in a pedicellaria cluster around a spine of a sea star, possibly Pycnopodia helianthoides. These small pedicellariae respond to contact stimulation by biting, as evidenced by the one that fastens quite firmly to the end of the pin. Note that the entire cluster can be dragged around with the pin being held by this single pedicellaria. Other types of sea-star pedicellariae may respond to chemical stimulation, as is the case with the different types in sea urchins. Research on functions of pedicellariae in west-coast sea stars appears not to have been done.

NOTE  the video replays automatically

 
Research study 2
 

photograph of sea star Solaster dawsoni chasing an intended prey sunflower star Pycnopodia helianthoidesThe sun star Solaster dawsoni is a major predator of other sea stars.  Studies at Bodega Marine Laboratory, California show that most intended asteroid prey run from contact with Solaster, including small specimens of ochre stars Pisaster ochraceus and even large specimens of sunflower stars Pycnopodia helianthoides, as shown in the photo on the Left.  Larger-sized P. ochraceus and all P. brevispinus apparently will stand their ground and use their pedicellariae against Solaster whenever contact occurs. Van Veldhuizen & Oakes 1981 Oecologia 48: 214.

There must be more to it than this, however, as Pycnopodia has abundant pedicellariae of its own, of 2 distinct types, but still runs from Solaster (see photographs on Right). Do the pedicellariae of Pycnopodia function differently than those of Pisaster spp.? or do different types of asteroid pedicellariae have different effects on Solaster? Further research is needed on this topic.photographic collage showing close view of pedicellariae of a sunflower star Pycnopodia helianthoides








Sunflower star Pycnopodia helianthoides avoiding
contact with the nematocysts of a sea anemone.
The inset shows skin detail ofPycnopodia's arm:
many soft brown gas-exhanging organs or dermal
papulae
are interspersed with spines bearing extended
rosettes ofsmall pedicellariae, all open, and a few
larger vice-like pedicellariae, mostly open 5X

 
Research study 3
 

photograph of sea star Stylasterias forreridrawing of pedicellaria clusters of sea star Stylasterias forreriPedicellariae in sea stars either operate like a pair of scissors or a pair of forceps.  An example of the former are the so-called crossed pedicellariae of the sea star Stylasterias forreri which are  structured in such a way as to be able to catch small fishes. The primary diet of Stylasterias seems to be snails, chitons, and other invertebrates, so perhaps the catching of fishes, although well documented, may be incidental to a primary defensive function of the pedicellariae. 

The pedicellariae are positioned in groups of 40 or so around spines on the upper arm surfaces.  At rest, the pedicellariae lie in rosettes at the bases of the spines.  On stimulation, such as drawing of jaws of pedicellaria of sea star Stylasterias forreri showing operating musculaturethe presence of a fish coming to rest on the spines, the rosettes are elevated and the pedicellariae opened (see drawings upper Right). 

There are 4 main muscle groups that operate the pedicellaria photomicrographs of a pedicellaria of the sea star Stylasterias forreri(see drawing lower Left): 2 sets of abductors whose contractions open the jaws, 1 set of adductors which contract to close the jaws, and 1 set of stringy adductors that have multiple functions of closing the jaws and positioning the pedicellaria at different angles.  Note also that pull on these stringy muscles, such as by a prey struggling in the jaws, will lock the jaws even more firmly. The means of elevating the pedicellariae is not well understood, but may be by contraction of longitudinal muscles in the skin covering the spine. Chia & Amerongen 1975 Can J Zool 53: 748. Photograph of Stylasterias forreri courtesy Chris Gunn, North Island Explorer, Campbell River, British Columbia northislandexplorer.com.

NOTE  with over 200 clusters per arm, there are more than 40,000 pedicellariae on the sea-star’s surface, certainly enought to hold a small fish.  The pedicellariae bite at and hold the fins. The fish is slowly moved around to the mouth by the tube feet and twisting of the arms, and ingested.  More on this topic can be found at FEEDING, GROWTH, & REGENERATION: PREY RESOURCES: STYLASTERIAS

 
 
3-D drawing of a pedicellaria cluster around the spine of a sea star taken from a video

CLICK HERE to see a video of operation of a pedicellaria cluster around the spine of a forcipulate sea star such as Stylasterias, Pycnopodia, or Orthasterias.

NOTE  the video replays automatically

 
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