Predators & defenses
 

Little work has been done on predators and defenses of west-coast feather stars.  Defenses include autotomy, swimming, a highly calcified body that is poor in nutritional content, and possibly the presence of unpalatable chemicals. Studies on the first 3 topics are considered in this section.

NOTE  no work on chemical defenses appears to have been done on west-coast crinoids.  However ,in this regard, certain Indo-Pacific comatulid crinoids possess sulphated polyketides (e.g., anthraquinoine-2-suphonate and sodium 2-hydroxy-anthraquinone sulphate) that deter feeding of fishes at physiological concentrations.  Rideout et al. 1979 Experientia 35: 1273.

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  Autotomy
 
Research study 1
 

photograph of sunflower star Pycnopodia helianthoides...a predator of feather stars?Arm loss through autotomy is common in west-coast Florometra serratissima, but what causes it?  Reports on European species list wave action, moving debris including seaweeds, high temperatures and other physiological stressors (including UV light), and disturbance by animals. As Florometra is rarely found in waters shallower than 20m, none of the physical factors listed are likely to influence them.  Potential predators are more likely to be the cause.  The author describes attacks on Florometra by predatory sea stars Pycnopodia helianthoides resulting in arm loss, and a single encounter with a spider crab Oregonia gracilis in the field that may have resulted in arm loss.  Mladenov 1983 Can J Zool 61: 2873.

NOTE the process of autotomy can be found elsewhere in this section of the ODYSSEY: LEARN ABOUT FEATHER STAR: REGENERATION

 

 

 

Sunflower star Pycnopodia helianthoides...a predator of feather stars? 0.4X

 

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Research study 2

 

photograph of feather star Florometra serratissima showing broken arm facing into cameradrawing of autotomy location in cirrus of feather star Florometra serratissima courtesy Holland & Grimmer 1981 Zoomorph 98: 169
Autotomy in Florometra serratissima can occur at several specific breakage locations along the arms and cirri.  The arms and cirri are comprised of skeletal ossicles joined by ligaments and other connective-tissue fastenings (see drawing above Right). Each ligament consists of thousands of fibers running parallel to the long axis of the cirrus.  Each fiber is a bundle of collagen fibrils along with associated interfibrillar material including cells known as fibroblasts.  A large nerve travels the length of each cirrus and arm, penetrating each ossicle at its centre and sending branches into the ossicles. The special autotomy locations are characterised by ligament fibers of collagen and nerve axons filled with presumed neurosecretory granules.  Fibers vary in length depending upon the diameter at the autotomy site, but are in the range of 50-75┬Ám. 

drawings of autotomy locations in cirrus of feather star Florometra serratissima courtesy Holland & Grimmer 1981 Zoomorph 98: 169Studies on specimens of Florometra collected at La Jolla, California and Bamfield, British Columbia indicate that the process of autotomy involves a massive exocytosis of granules at the site stimulated by neural transmission (see drawing below Right).  The released neurosecretions, which could contain chelating agents, strong acids, and proteolytic enzymes or enzyme activators, is thought to liquify the ligament fibers, fibroblasts, and other connective tissues, leading to loss of the cirrus or arm.  The calcareous ossicles on either side of autotomy site show signs of erosion. On stimulation of an arm tip in an intact specimen, such as by crushing or cutting with scissors, the proximally closest autotomy site breaks after about 1sec.  Holland & Grimmer 1981 Zoomorph 98: 169.

NOTE  the authors term these zyzygies, defined as ordinarily strong joints that lose tensile strength by an intrinsic mechanism acting suddenly and causing autotomy

NOTE in the arm this is known as the brachial nerve

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  Swimming
 
Research study 1
 

photograph of swimming feather star Florometra serratissima
The only information on specific defenses in west-coast crinoid Florometra serratissima s comes from anecdotal references to swimming on contact with sunflower stars Pycnopodia helianthoides or crabs that wander through an aggregation. Contact with Pycnopodia, for example, is followed by about a 5-sec delay, after which several power strokes carry the stimulated individual 1-2m distance.  This cycle can be repeated several times and capture by a sea star is actually thought to be rare. Mladenov 1983 Can J Zool, Lond 61: 2873.

 

 

 

 

A swimming feather star
Florometra serratissima
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  Nutritional value
 
Research study 1
 

A crinoid really is just "skin and bones", yet no studies have been done directly on the poor nutritional return that a predator would get from a meal of crinoid. Yet, a species like Florometra serratissima will swim from contact with various animals including ones that attempt to capture them, so it seems that at least some predators find them to be tasty.

NOTE for information pertinent to this subject see LEARN ABOUT NUDIBRANCHS:DEFENSES: NUTRITIONAL CONTENT

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