Sipunculus (Sipunculus) nudus Linnaeus, 1766
Sipunculus nudus is considered a cosmopolitan species found in all oceans from intertidal zones to 900 m depth. It is the most known species in this genus. Common and easily collected along the Atlantic and Mediterranean coasts of Europe, it has been studied for many decades by developmental biologists, physiologists, and biochemists (Cutler, 1994). The surface of the trunk of species in this genus has a checked appearance resulting from the intersection of the longitudinal and circular muscles, and has an iridescent pink or sepia color (live specimens).
The original description by Linnaeus (1766) of S. nudus reported the type locality as the European ocean. Nevertheless in the revision of the genus Sipunculus, Cutler & Cutler (1985) refers only to the type of S. titubans, a species considered by them as conspecific with S. nudus. This type specimen was collected in Puntarenas, Costa Rica.
Sipunculus titubans type is located at Museum für Naturkunde, Humboldt-Universtät, in Berlin, under the number MNHU 1036.
(From Stephen & Edmonds, 1972; Ditadi, 1982 and Cutler, 1994)
Introvert shorter than the trunk. Triangular papillae (scale-like) posteriorly directed covering the surface of the introvert.
The trunk is cylindrical measuring 184 ± 53 mm of length. Trunk diameter/length ratio averages 1:16. The surface of the trunk is cut into a large number of small rectangles by the intersection of the longitudinal and circular muscles.
Glans region (a smooth posterior tip) present on the posterior end of the trunk.
Tentacular crown in live specimens consists of two pairs of pinnate tentacles, with dorsal pair longer than the ventral pair. Preserved specimens present a highly wrinkled membrane. The body of adult live worms has an iridescent pink or sepia color, and the younger ones a whitish color.
24-34 longitudinal muscles bands (LMBS), more commonly 28-32. The LMBs usually split in the glans region.
Circular muscles divided in narrow bands.
A pair of nephridia partially attached (10-40%) to the trunk wall.
The brain is bilobed, width greater than length, with a dorsal brain process, which is digitate or a spongelike mass.
Two pairs of short retractor muscles arise at the same level. According to Stephen & Edmonds (1972) the ventral pair usually spreads over the 2-5 bands and the dorsal over 9-12.
Spindle muscle arises anterior to the anus, attached to the rectal caecum and is not attached to the posterior end of the trunk.
A common size of S. nudus is between 5-15 cm long (Cutler, 1994). Brazilian specimens of S. nudus can reach 20 cm of length (Ditadi, 1982).
Ecology and Distribution
This is a cosmopolitan species found in all oceans from intertidal zone to 30 m. There are a few records from 100-900 m (Cutler, 1994).
Habitat and Ecology
(From Ditadi, 1982)
This species lives in muddy or sandy beaches in non-permanent galleries at a mean depth of 30 cm. The gallery entrances are marked by one, two or sometimes three openings. Specimens recently collected in Fort Pierce, Florida, was found in a sand flat, in an exposed intertidal zone, during low tide (Kawauchi, personal observation).
There are three species of copepods from the genus Myzomolgus associated with Sipunculus nudus. Myzomolgus stupendus and M. tenuis were found in Channel, coast of France (Bocquet & Stock, 1957) and in Korea (Kim, 2001). In Brazil, another species of Myzomolgus (M. sipunculensis) was described associated with S. nudus and S. phalloides.
Sipunculans, commonly of the genus Sipunculus, are used by humans in two different ways, as food or as fish bait. In Xiamen in Fujian province of the People’s Republic of China, a seaboard city in the southeast China, there is a special delicacy dish in which the main ingredient consists of sipunculans. The sipunculan worm jelly is prepared with sipunculans from the genus Sipunculus (probably S. nudus). As is the case for some other organisms such as eels, sipunculans form a protein gel when cooked (Food preservation, 2010). The preparation of this typical dish consists of cleaning the sipunculan worm by eliminating the intestine full of sediment, followed by braising in a slow fire, and transferring to cups for cooling. People consume this dish with chili sauce, mustard sauce, and vinegar (Xiamen Travel Information, 2010).
In some countries fishermen use sipunculans as bait. In Brazil the fishermen collect the worms from their burrows by digging in the sediment during a period of low tide .In Europe fishermen may obtain the worms more easily by purchase from a bait machine that provides live worms, including samples of Sipunculus. Popularly known as titas, tatas, bibi, they are imported in large numbers from China or Vietnam to Europe to serve as bait for recreational purposes.
Besides humans, sipunculans are a source of food for many fishes. Among invertebrates there are a few such as gastropods and asteroids that may fed on sipunculans as part of their diet. (Kohn, 1975).