Leptasterias aequalis (Stimpson, 1862)

Common Names:  Colorful six-rayed star, six-rayed Star, broad six-rayed star, delicate six-armed star

Synonyms: Leptasterias aequalis is thought to be a hybrid between L. hexactis and L. epichlora.
Phylum Echinodermata
 Class Asteroidea
   Order Forcipulatida
     Family Asteriidae
Leptasterias aequalis from lower intertidal of Sares Head, 6-2011.  Total arm spread 4 cm.
Photo by: Dave Cowles, June 2011
Description:  This species generally has six rays and an arm radius to 5.2 cm.  The color of the aboral surface is extremely variable, from olive-green, indigo or gray to coral-red (as here) or orange and usually mottled.  The arms (rays) appear relatively broad and heavy when the animal is moving, and the aboral spines (ossicles) are flattened and mushroom-shaped (photo).  Pedicellariae on the aboral surface are numerous and randomly arranged around the aboral spines (photo).

How to Distinguish from Similar Species:   Species of Leptasterias are very hard to tell apart, and L. aequalis is probably a species complex.  This species is very similar to Leptasterias pusilla but can be distinguished by its large, flat aboral spines, thicker arms, and darker color. L. hexactis is usually olive-green or indigo, and its pedicellariae are embedded in tissue at the base or midway up the aboral spines.  L. epichlora is usually mottled and blue-gray, dark green, or indigo and its pedicellariae are few and randomly arranged around the aboral spines.

Note from Kozloff, 1996:  "Specimens keying to Leptasterias hexactis are now believed to belong to three recognizable entities.  They are distinguished to some extent by biochemical properties, but the following visible features will usually enable one to separate them.  Leptasterias hexactis (Stimpson, 1862):  small pedicellariae (as distinguished from larger pedicellariae) especially abundant around the aboral spines, generally embedded in tissue either at the base or about midway on the spines, and forming a characteristically wreathlike arrangement; color of aboral surface usually dark olive-green or indigo. Leptasterias epichlora (Brandt, 1835):  small pedicellariae few and randomly arranged around the aboral spines; color of aboral surface commonly indigo, blue-gray, or dark green, usually mottled.  Leptasterias aequalis (Stimpson, 1862) (believed to be a hybrid of L. hexactis and L. epichlora):  small pedicellariae usually numerous and randomly arranged around the aboral spines; color of aboral surface extremely variable, ranging from olive-green, indigo, or gray to coral-red or orange (in our region, the last two colors not often noted in the other two species)."

Geographical Range:   L. aequalis ranges from Vancouver Island, southern BC. Canada to Santa Catalina Island in the Channel Islands, southern CA.

Depth Range:  Intertidal zone under rocks or algae.

Habitat:  Common on rocky shores that are exposed to the surf.

Biology/Natural History:   L. aequalis is known to cling very tightly to rocks and it has the ability to conform closely to irregularities in the surface.  It is a carnivore and feeds on sea cucumbers, littorine snails, limpets, chitons, small mussels, barnacles, and other small animals, including dead animals.  L. aequalis often selects large, hard to capture prey that is often rich in calories.  This type of prey supplies most of the sea star’s energy.  It is often in direct competition with the much larger sea star, Pisaster ochraceus for food.  Breeding occurs from November to April in the Puget Sound.  The eggs are yellow, yolky, and about 0.9 mm in diameter.  A unique feature of this species is that the broods of eggs (ranging from 52 – 1,491 eggs, variable based on the size of the female) are held by the female in the region of the mouth below the central disk.  Because of this, brooding females cannot flatten themselves against the substratum and are only anchored by their outermost tube feet.  Unfortunately, they are often dislodged by the waves, losing their eggs.  It is necessary for the female to clean the egg masses, and if she does not do this then the eggs quickly die.  The presence of the eggs blocks the female’s mouth and she will not feed while brooding, even if there is food readily available.  The development of the embryos is direct and individuals reach maturity within 2 years.



 
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References:
Dichotomous Keys:
  Carlton, 2007
  Kozloff, 1987, 1996.

General References:
  Harbo, 2011
  Kozloff, 1993.
  Lamb and Hanby, 2005
  Lambert, 2000
  Morris et. al. 1992.
  Sept, 1999

Scientific Articles:
Chia, F. S., 1966.  Systematics of the six-rayed sea star Leptasterias in the vicinity of San Juan Island, Washington.  Systematic Zool. 15: 300-306

Kwast, K.E., D.W. Foltz, and W.B. Stickle, 1990.  Population genetics and systematics of the Leptasterias hexactis (Echinodermata: Asteroidea) species complex.  Mar. Biol. 105: 477-489



General Notes and Observations:  Locations, abundances, unusual behaviors, etc.:


Another individual with a reddish coloration.
Photo by Dave Cowles, July 2005


The oral side of the individual above.


An underwater photo by Kirt Onthank, June 2007


This closeup of the aboral side of the central disk shows the multitude of ossicles, including spines and pedicellariae.  Sacklike papulae are seen as well, as is the madreporite.



This even closer view shows details of the spine ossicles with their mushroom-shaped tips, and the pedicellariae.



Closeup view near the madreporite.
 


Tip of a ray, aboral view.

Large

This large individual is about 10 cm in diameter.  Photo by Dave Cowles, July 2012



Authors and Editors of Page:
Melissa McFadden (2002):  Created original page
Edited by Hans Helmstetler  12-2002, Dave Cowles 2005, 2011