|Dolioletta gegenbauri Uljamin, 1884 : Doliolid
Phylum Chordata / Subphylum Urochordata / Class Thaliacea / Order Doliolida / Family Doliolidae
If you see a small (up to about 9 or 10 mm long), transparent barrel-shaped gelatinous creature that has a quick, jumpy motion, it’s probably a doliolid. North of Point Conception in California, the species most likely to be seen is Dolioletta gegenbauri. Most individuals encountered are gonozooids, which are solitary hermaphrodites. They possess 8 distinct muscle bands that circle the entire body. Solitary gonozooids produce the oozooids, which are usually seen in fewer numbers within the population. Oozooids are distinguished by an conspicuous tail of asexually produced zooids, and have 9 circumferential muscle bands. This stage is known as the “nurse”. The tail has lateral rows of nutritive gastrozooids and a median row of phorozooids. Other zooids then attach to the phorozooids and are carried away together, where they develop into gonozooids. After the gonozooids mature, they separate from the phorozooids and serve their role in producing more oozooids. Why doliolids go through such a complicated reproductive mess is anybody’s guess, but the result can be lots of doliolids.
Using a mucous net, Dolioletta is a very adept filter feeder on particles ranging up to 100 micrometers in size. Gill slits are located within the relatively large pharynx, which also holds the mucus secreting endostyle. Water is pumped through the mucous net by the action of gill cilia. With their efficient filtering mechanism, dense aggregations of this species can quickly deplete phytoplankton within a wide area. When food is plentiful, Dolioletta is amazingly prolific, with a single oozooid capable of producing thousands of gonozooids in a matter of days. This species can form dense swarms of up to an average of 500 per cubic meter, and may be the most abundant pelagic tunicate off the California coast. It is the most cold tolerant of all the doliolids, ranging farther north than any other species. Although usually oceanic, occasionally dense swarms may inundate nearshore waters. On close approach, their presence is usually revealed when the doliolid attempts to dart away using rapid contractions of the body muscles.
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