Leptasterias hexactis

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. 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 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).

This species generally has six rays and an arm radius to 5.2 cm. The aboral surface usually appears dark olive-green or indigo.. The arms appear relatively broad and heavy when the animal is moving, and the aboral spines are flattened and mushroom-shaped. These spines are generally arranged so densely that they largely obscure the aboral body wall and the pedicellariae, but sometimes the pedicellariae can be seen (photo).

Geographical Range: L. hexactis resides as far north as the San Juan Islands and the Strait of Juan de Fuca in Washington to Santa Catalina Island in the Channel Islands, California.

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.

Known from seamounts and knolls

Depth range based on 84 specimens in 3 taxa.
Water temperature and chemistry ranges based on 63 samples.

Environmental ranges
  Depth range (m): -0.1 - 40
  Temperature range (°C): 9.481 - 10.345
  Nitrate (umol/L): 5.634 - 6.931
  Salinity (PPS): 31.692 - 32.028
  Oxygen (ml/l): 6.535 - 6.656
  Phosphate (umol/l): 0.883 - 1.030
  Silicate (umol/l): 12.975 - 18.436

Graphical representation

Depth range (m): -0.1 - 40

Temperature range (°C): 9.481 - 10.345

Nitrate (umol/L): 5.634 - 6.931

Salinity (PPS): 31.692 - 32.028

Oxygen (ml/l): 6.535 - 6.656

Phosphate (umol/l): 0.883 - 1.030

Silicate (umol/l): 12.975 - 18.436
 
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Depth Range: They reside in the 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.