Leptasterias hexactis (Stimpson, 1862)
|Top view of individual collected at Sares Head, WA in the lower intertidal zone. Diameter approximately 3 cm.|
|Photo by: Dave Cowles, Sept 2005|
How to Distinguish from Similar Species: This species is very similar to Leptasterias pusilla but can be distinguished by its large, flat aboral spines, thicker arms, and darker color. L. epichlora is usually mottled and blue-gray, dark green, or indigo and its pedicellariae are few and randomly arranged around the aboral spines. L. aequalis is thought to be a hybrid between L. hexactis and L. epichlora. It has many small pedicellariae randomly arranged around the aboral spines, and a variable aboral color ranging from olive-green, indigo, or gray to coral-red or orange.
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 feathres 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. hexactis resides as far north as the San Juan Islands and the Strait of Juan de Fuca in Washington south to Santa Catalina Island in the Channel Islands, California.
Depth Range: Middle intertidal zone, often in small beds of mussels (Mytilus californianus). L. hexactis can often be found sheltered under rocks or algae at very low tides or on sunny days.
Habitat: This species is common on rocky shores that are exposed to the surf.
Biology/Natural History: L. hexactis 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. hexactis 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 (photo). 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 (photo of juveniles) and L. hexactis individuals will reach maturity within 2 years. Experiments with the behavior of L. hexactis have shown that if the nerve ring is cut at two opposite points, then the animal will walk apart until fission occurs.
Leptasterias hexactis is fleshy, with large papulae
and a stronger, coarser skeleton than is Henricia
leviuluscula, another intertidal seastar of similar size.
It seems to rely much less on its madreporite
to take up seawater for maintaining its tissue fluid balance. It
probably uses osmotic uptake of fluid through the papulae
instead (Ferguson, 1994).
|Main Page||Alphabetic Index||Systematic Index||Glossary|
Morris et. al. 1992.
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
Ferguson, John C., 1994. Madreporite inflow of seawater to maintain body fluids in five species of starfish. pp. 285-289 in Bruno David, Alain Guille, Jean-Pierre Feral, and Michel Roux (eds). Echinoderms through time. Balkema, Rotterdam.
Flowers, Jonathan Mark, 1999. Discordant patterns of genetic and morphological variation and their implications for the taxonomy of Leptasterias subgenus Hexasterias of the north Pacific. M.S. Thesis, Louisiana State University. 57 pp.
Foltz, D.W., 1998. Distribution of intertidal Leptasterias spp. along the Pacific North American coast: A synthesis of allozymic and mtDNA data. pp. 235-239 in Rich Mooi and Malcolm Telford (eds), Echinoderms: San Francisco. Proceedings of the Ninth International Echinoderm Conference, San Francisco, California USA 5-9 August 1996.
Foltz, David W. and William B. Stickle, Jr., 1994. Genetic structure of four species in the Leptasterias hexactis complex along the Pacific coast of North America. pp. 291-296 in Bruno David, Alain Guille, Jean-Pierre Feral, and Michel Roux (eds). Echinoderms through time. Balkema, Rotterdam.
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
Stickle, William B., Jr. and David W. Foltz, 1994. Habitat affinities of species in the Leptasterias hexactis complex along the Pacific coast of the continental United States. pp. 353-358 in Bruno David, Alain Guille, Jean-Pierre Feral, and Michel Roux (eds). Echinoderms through time. Balkema, Rotterdam.
Mejia, Jose, 2006. Leptasterias hexactis orientation and movement: Unidirectional or sporadic. Jose Mejia tested this species to see whether they crawl toward a preferred arm. He repeatedly placed 20 seastars on a target marked in 1 cm increments, then recorded the direction they crawled toward, the leading ray during crawling, and the distance they crawled within 2 minutes. He repeated the test 6 times for each seastar, starting with a different arm pointing south each time. The arms were numbered so that, while looking at the aboral side, the arm nearest but to the right of the madreporite was designated arm 1, that to the left of the madreporite was arm 2, an so on around to arm 6. He found that there was a definite preference about which arm to lead with. With most individuals it was arm 1 or 2, though some individuals chose other leading arms. Individual seastars tended to choose the same (or adjacent) leading arms repeatedly. He found no preference for compass direction crawled, indicating that none of the environmental characteristics of the tank such as light or current were affecting the results.
The oral side of the individual above.
Although individuals usually have 6 rays, they may sometimes have 5 or 7 rays such as this individual from Sares Head.
This closeup of the general body surface shows the sack-like papulae (coelomic sacks) that seastars such as this one extend for respiration and waste removal. Among the bases of the papulae can be seen shorter, pincerlike pedicellariae. Photo by Dave Cowles, July 2008
This closeup of the madreporite area show clearly what the madreporite is: a filter screen leading to the water vascular system. Around the madreporite can be seen a number of partly retracted papulae (one on the left is fully extended) and several pedicellariae. Photo by Dave Cowles, July 2008
The following set of photos were taken by Dave Cowles of L. hexactis
being used in an experiment by Tamara Loveday. The seastars had been
collected from rocks near Rosario December 2, 2009. They were kept
in an aquarium at 8 degrees C. The photos were taken April 21, 2010.
Here is a timetable of some events noted by Tamara:
Seastars collected: December 2, 2009
Females first started brooding eggs: Late December or early January
The first juveniles began appearing: February. The juveniles at first stayed under the mother but gradually moved away, still attached to the aquarium walls
Juveniles began detatching, floated free at the surface as neuston: Early April
This brooding female, seen fron the underside through aquarium glass, is brooding eggs. She is about 5 cm in span. Two juvenile seastars which have left another nearby mother are attached to the glass near her.
This closeup of another female shows how she holds the eggs near her mough, under the central disk. The eggs are about 1 mm diameter.
The eggs under this brooding female have all developed into juveniles. Most are still staying under her but some have begun to migrate away.
This closeup shows a mass of juveniles still sheltering under the mother, while several more are a short distance away.
Here are some juveniles which have migrated away from the mother but are still attached to the aquarium sides.
|More photos of juveniles which have migrated away from the mother. They are both about 2 mm in span|
This is a photo of juveniles which have released from the aquarium walls and are floating as neuston on the surface of the water. The photo is looking up through the aquarium walls toward the water surface above. The underside of some females clinging to the aquarium glass can be seen in the foreground, and the aboral surface of several seastars or their reflections can be seen in the background. The scattered dots are juvenile seastars riding around on the water surface as neuston.
|These photos are of juveniles which were floating as neuston. They were about 2 to 2.5 mm in span.|