This page links to photos of tunicates, sometimes called sea squirts, we have seen in the Marshall Islands. We did not make a special effort to photograph or record members of this group, but there are many species in the Marshalls, and probably only a relatively small proportion of them are recorded here. As can be seen from the photos, tunicate body form is quite variable, but there are additional planktonic forms such as salps that as of this writing, we have not yet covered. The species below are all sessile forms, living attached to reefs, marine growth or man-made objects (e.g., pier pilings), and make a living filtering water for planktonic food. They are sometimes mistaken for sponges, but are very different morphologically and developmentally. Indeed, tunicates belong to the animal phylum Chordata, whose other major group includes all the vertebrates: fish, amphibians, reptiles, birds and mammals. Hence, they are more closely related to us than any of the other marine invertebrates. A hint of this relationship is visible in tunicate development. Some tunicate larvae resemble frog tadpoles, are able to swim, and possess a notochord, a structure that in vertebrates becomes part of the vertebral column. In tunicates, however, this mobile stage is just used for dispersal, and soon the swimming larva settles down and attaches to a suitable substrate before morphing into the adult filter feeding form. Some species are solitary while others are colonial and can further grow and reproduce by budding. A typical solitary tunicate has an ovoid or elongate body with two openings, called branchial (also called oral or buccal) and atrial (or cloacal) siphons. Water is drawn in the branchial siphon, passes through a filter to collect the plankton, and then goes out the atrial. Many of the colonial forms have their bodies (called zooids) fused together with each zooid containing a branchial opening and a tube that connects to a common area with a single atrial opening that supports many zooids. As a colony grows, more atrial openings can develop, each connected to a number of separate zooids.
Tunicates tend to be not thoroughly covered in popular web and print publications, and names given are sometimes contradictory. We have picked and chosen names primarily from the references listed at the bottom of this page, sometimes modified by what we have encountered in various other websites, but we are certain that not all our identifications are accurate. We welcome corrections at uwkwaj@yahoo.com. The thumbnails below link to pages with additional, larger photographs.
Order APLOUSOBRANCHIA
Order PHLEBOBRANCHIA
Order STOLIDOBRANCHIA
Order SALPIDA
Order Unknown
Primary references for identification:
Colin
& Arneson (1995)
Gosliner
et al (1996)
Ascideacea. From website Marine
Biodiversity Survey of Guam and the Marianas.
iNaturalist
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