Introduced Marine Species of Hawaii
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  Ascidia sydneiensis (Gray sea squirt)
Ascidia sydneiensis

Phallusia nigra

Diademnum sp.

Phallusia nigra Savigny, 1816

Phallusia nigra on a floating dock in Keehi LagoonBlack sea squirt

Phylum Chordata
Subphylum Urochordata
Class Ascidiacea
Order Enterogona
Family Ascidiidae

This common large solitary ascidian is typically a velvety black or dark brown. Small specimens or individuals growing in shaded areas may be a translucent gray with scattered spots of blank pigment. P. nigra adheres to the substrate by it's posterior left region. It's right has a thick, cartilagenous, smooth tunic with prominent blood vessels. The siphons are separated by a third to half the body length. Removing the tunic reveals evenly distributed musculature on the right mantle. A large individual will have around 50 oral tentacles (from Abbott et al. 1997).
musculature and neural duct of Phallusia nigraHabitat
Common in harbors and embayments, P. nigra lives in shallow water attached to any available hard substrate such as dead coral, pier pilings, or floats.
Hawaiian Islands
Throughout the main islands, primarily in harbors.
Native Range
Tropical western Atlantic
Present Distribution
Tropical western Atlantic, Mediterranean, Indian Ocean, Micronesia, and Hawaiian Islands
Mechanism of Introduction
Unintentional, as fouling on ships' hulls
Fouling organism. Ecological impact unstudied, probably competes for space with other fouling and shallow-water invertebrates.
This species is hermaphrodite, with a simple reproductive system. Fertilization is external, and after a time in the plankton the free-swimming tadpole larvae will settle and metamorphose.
Ascidians are suspension feeders that use a mucous net to filter plankton from the water. Ciliary action moves water into the oral siphon and to the pharynx which resembles a basket. As water is pumped through slits in the pharyngeal basket, out the atrial siphon, it passes through a layer of mucous coating the inside. When the mucous sheet is clogged with food, special structures pass it to a short esophagus and into the stomach.
The first records of this common large (to 9 - 10 cm) dark solitary ascidian, appear to date from 1968-1972, with the report of "Ascidia melanostoma" from fouling panels off of Oahu at 15 meters depth and in Pearl Harbor at 9 meters by Long (1974); Abbott et al. (1997) consider it probable that these records represent morphological variants of P. nigra (Ascidia melanostoma being otherwise unknown from the Islands).
Abbott et al. (1997) noted that P. nigra "lives on rocks and dead coral on barely subtidal mudflats in Kaneohe Bay and on floats and pilings there and in Pearl Harbor and in the Keehi boat harbor". They further note that the color of P. nigra, while a consistent velvety black in the tropical western Atlantic Ocean, varies in the Hawaiian Islands, with individuals in shady places having translucent gray tunics.
The origin of Phallusia nigra is unclear; it may be native to the Red Sea (its type locality) and the Indian Ocean area, or to the tropical western Atlantic Ocean, where it occurs from Florida to Brazil (Abbott et al., 1997). It also occurs in Micronesia. Earlier records from Australia are now referred to other Phallusia species
Abbott, D.P., A.T. Newberry, and K.M. Morris. 1997. Section 6B: Ascidians (Urochordata). Reef and Shore Fauna of Hawaii. Bishop Museum Special Publ. 64 (6B).
Long, E.R. 1974. Marine fouling studies off Oahu, Hawaii. Veliger. 17: 23-39.


© 2002 Hawaii Biological Survey, Bishop Museum