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Phylum Urochordata
Class Appendicularia


  • Also called larvaceans.
  • Small, solitary, free-swimming tunicates.


  • < 5 mm.

Distinguishing characteristics

  • Characterised by the retention in the adult of a muscular tail and a notochord, a rudimentary or embryonic spinal column typical of all chordates.
  • Body is divided into two sections: the trunk and the tail.
  • Sexually mature appendicularian resembles the larval chordate form.


  • Appendicularians are common in most oceans, coastal waters and estuaries, often occurring in large numbers and are well adapted for living in oligotrophic waters (those with low nutrient levels and hence low productivity).
  • South-eastern Australian waters (Dakin and Colefax 1940, Thompson 1948, O’Sullivan 1983).
  • Thompson (1948) reported 8 species of appendicularians in south-eastern Australian waters including Oikopleura longicauda, Fritillaria pellucida and Fritillaria haplostoma, species which are both very abundant and widely distributed.
  • Tokioka (1960) noted that Fritillaria haplostoma is a typical neritic or coastal species of appendicularian.


  • Build delicate, gelatinous houses, several times the body length of the animal, in which are incorporated elaborate structures used to filter food from the water.
  • Tail is used both as a means of locomotion and to generate the feeding current which passes through the filters inside the house.
  • Houses of appendicularians are rarely seen or captured in plankton samples as they are easily damaged during collection.
  • Also, despite occurring in very large numbers, the appendicularians themselves are often not recognised, because of their small size, and also due to the trunk and tail often becoming separated.
  • The delicate filtering mesh of the appendicularian house can concentrate pico- and nano-plankton (particles between 0.2 and 20 millionths of a metre), and particulate matter to approximately 100 to 1000 times the ambient concentration (Davoll and Silver, 1986; Bedo et al., 1993).
  • Houses need to be discarded as often as several times per day, as the mesh becomes clogged with particulate matter plus various protozoans, auto- and heterotrophs, and small metazoans.
  • Discarded houses are one of the major sources of marine snow, which is the name given to aggregations of suspended organic particles in the ocean (Davoll and Silver, 1986; Alldredge and Silver, 1988).
  • Both the discarded houses and the appendicularians themselves are consumed by carnivorous zooplankton and adult and larval fish (Gorsky and Fenaux, 1998).
  • Appendicularians also produce a high number of small faecal pellets per day (Vargas et al., 2002), an ideal food source for other zooplankters.
  • Appendicularians thus play an important role in accumulating material that would otherwise be too small for direct consumption by filter feeders and carnivores.
  • All species of appendicularians, except Oikopleura dioica, are hermaphroditic, but self-fertilization is not possible.
  • Appendicularians die after spawning.
  • Identification to species level can be difficult for beginners. However, the shape of the trunk and tail may help to distinguish the three families likely to be found in south-eastern Australian waters.