Overview

Key Features:

S. montereyensis can be distinguished from similar species of tunicates, be-cause its siphons are close together at distal end; the oral siphon is re-curved (pointing to the side or downward) and the atrial siphon is straight (pointing upward).

Primary Common Name:

Stalked tunicate

Synonymous name(s):

Cynthia montereyensis, Tethyum montereyensis

General Grouping:

Sea squirts

Geographic Range:

Vancouver Island to Baja California.

The stalked tunicate can be found north to Ucluelet (Vancouver Island) and Hope Island (British Columbia), and south to Isla San Geronimo (Baja California).

Intertidal Height:

0 to 0 feet (0 to 0 meters)

Subtidal Depth Range:

Minimum Depth: 0 meters or 0 feet
Maximum Depth: 30 meters or 99.9 feet

Habitats:

bay (rocky shore), kelp forest, protected rocky shore

Notes:

Stalked tunicates can be found fairly commonly, attached firmly to solid substrata in calm to rough waters. They are found in shallow water areas where there are tidal currents. In the Pacific Northwest stalked tunicates are found primarily in outer straits and the open coast, but are rare in inland waters. S. montereyensis, can be found in depths ranging from the low intertidal zone, to about 30m.

Abundance:

Relative Abundance:

The sea squirt is locally common year round. It is an easily recognized and broadly dis-tributed solitary tunicate. Where it occurs at all, the stalked tunicate may be present in relatively large numbers, but in small densities.

Species Description:

General:

The stalked tunicate, Styela montereyensis has a cylindrical and elongate body, supported on a thinner stalk about equal to the body length. Overall length occa-sionally exceeds 25 cm in calm habitats but more often 8-15 cm in exposed sites. The stalked tunicate has a tough, leathery tunic with prominent longitudinal ridges and grooves running across the entire length of the animal, but otherwise relatively smooth. Stalked tunicates are yellow to dark reddish brown, and often fouled with other organ-isms and debris in harbors, but clean in wave swept areas.

Distinctive Features:

Although they just look just like slimy sacs, sea squirts are more closely related to humans than any other invertebrate group, because larval tunicates have several chordate structures, including a notochord and a nerve chord. Later these are lost, in most adult forms. There are two openings are found on the tunicate: the buccal siphon and the atrial siphon. Sea squirts get their name because a gentle squeeze causes water to shoot out of the atrial siphon. Sedentary adult forms can either be colonial or solitary. Tunicates have a long, tubular heart which contracts in two directions. The species may store vanadium in its tunic, about 36-40 ppm.

Size:

Height: up to 25 cm (10 in.) Width: 5 cm (2 in.)

Natural History:

General:

Despite bearing aragonite spicules, the fossil record of the sea squirts is largely lacking, and is only available from as far back as the Silurian period. Over the past few hundred years, the world\'s harbors have been invaded by non-native sea squirts, which have clung to ship hulls, or introduced other organisms such as oysters and seaweed. Several factors, such as a lack of predators, quick attainment of sexual maturity, and tolerance to a wide range of environments, allows sea squirt populations to grow quickly. Unwanted popula-tions on docks, ship hulls, and farmed shellfish, cause economic problems. Sea squirt in-vasions have disrupted the ecosystem of several natural subtidal areas by smothering na-tive animal species. Blood is pumped throughout the body, by a short tubular heart. For about 100 beats the blood flows in one direction, then after a short pause it starts flowing in the opposite di-rection. Tunicate blood has very high levelst of heavy metals, especially vanadium and iron, possibly to help deter predators. Gas exchange occurs through the body wall. There is no head, nervous system, and sensory organs are highly underdeveloped, but adequate for the sessile life style. Although the lifespan of stalked tunicates is unknown, observed specimens have lived for at least 3 years. Ascidian tunics are composed mostly of an acellular (not made of cells) tunicin matrix, similar to cellulose. There are some living cells of different varieties within this matrix but they are well spaced out. Usually, the tunic is attached to the substrate by a small holdfast and stands upright. It has two openings, an inhalant siphon and an exhalent siphon. On the inner surface of the tunic is a thin epidermis, which secretes the tunic. Inside of the epidermis is a thicker dermis, and then bands of longitudinal and circular muscle, these muscles squeeze the tunic, causing a jet of water to leave the exhalent siphon. This action may help deter predators. Stalked tunicates can become overgrown with growths of anemones, hydroids, and even other tunicates.

Predator(s):

Sea squirts are the natural prey of many animals, including nudibranchs, flatworms, mol-lusks, sea stars, rock crabs, birds, fish, and sea otters. Sea squirts are also eaten by humans in many parts of the world, including Korea, Japan, Europe, and Chile (where they are sold under the name "sea violet").

Prey:

Various small particles filtered from the water, such as plankton.

Feeding Behavior:

Sessile suspension feeder

Notes:

S. montereyensis has a branchial basket, which it uses as its way to construct a filter-feeding net out of mucus. The branchial basket supports the net and cilia on the edges of the gill slits, pulling water through it, helping the animal collect food. Sea squirts feed by taking water through their oral siphon. The water enters the mouth and pharynx, and then flows through mucus-covered gill slits, to a water chamber called the atrium, finally exiting through the atrial siphon. Water currents are maintained by hundreds of beating cilia, but can also be regulated by muscles.

Seasonal Behavior

Reproduction:

Nearly all sea squirts are hermaphrodites. Larval settlement and breeding, occur in the summer. Studies of developing eggs, have shown that the inner follicle of the oocyte, provides the test cells, which are enclosed with the ovum inside the chorion. Both sperm and eggs are shed to the sea. In natural situations, larvae settle best on surfaces which have been underwater, for at least several months. In metamorphosing larvae, the tail col-lapses as this is characteristic for members of the suborder Stolidobranchia.

Issues

Monterey Bay National Marine Sanctuary:

The exceptional filtering capability of adult sea squirts causes them to accumulate pollu-tants that may be toxic to embryos and larvae as well as impede enzyme function in adult tissues. This property has made them a sensitive indicator species of pollution. Sea squirts are valuable because of their unique evolutionary position; as an approximation of ancestral chordates, they can provide valuable information regarding chordate evolution. To deter predators, tunicates secrete various chemicals that are of pharmacological inter-est. Yondelis, a drug that was recently approved, was developed from tunicates to treat soft tissue sarcoma. Tunicates also transport carbon to the sea floor, in turn slowing the effects of global climate change.

References

• Carlton, J.T. 2007.
  The Light and Smith Manual, 4th edition
  Intertidal Invertebrates from Central California to Oregon
  University of California Press. 1001 p.
  
• Langstroth, L. and L. Langstroth. 2000. A Living Bay: The Underwater World of Monterey Bay. University of California Press, Berkeley and Los Angeles, CA. 287 p.
• Meinkoth, N.A. 1998. National Audubon Society Field Guide to North American Seashore Creatures. A.A. Knopf, New York, NY. 813 p.
• Morris, R.H., D.P Abbott, and E.C. Haderlie. 1980. Intertidal Invertebrates of California. Stanford University Press, Stanford, California. 690 p.
• Ricketts, E. F., J. Calvin, and J.W. Hedgpeth. 1985. Between Pacific tides. Stanford University Press, Stanford, CA. 652 p.
• WWW
  Crowles, Dave 2005. Walla Walla University
  http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Echinodermata/Class%20Asteroidea/Pycnopodia_helianthoides.html
  Accessed 3/31/09 for Pycnopodia helianthoides
  Accessed 9/12/09 for Stalked tunicate
  Accessed 8/29/09 for Blueband hermit crab
  
• WWW
  Zipcodezoo. The Bay Science Foundation 2009
  http://zipcodezoo.com/Animals/P/Pycnopodia_helianthoides
  Accessed 03/31/2009 for Pycnopodia helianthoides
  Accessed 08/19/2009 for Stalked tunicate
  Accessed 08/19/2009 for Blueband hermit crab
  Accessed 01/26/2010 for Pigeon Guillemot
  

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