(Forskål, 1775)

Description
— Aggregate form with anterior end of body rounded, the posterior end is somewhat fusiform. The test is bluntly pentagonal and never echinate. M1-M3 and M4-M5 are fused mid-dorsally; both groups of muscle bands are separated in lateral view. The nucleus has a posterior projection. The test is pentagonal posteriorly. The number of muscle fibres in M1-M5 is 15-17, normally 16. The atrial opening is not central and there is a posterior lateral protuberance on one side only.
— Solitary form with smooth test, atrial palps simple and straight; lateral projections small, medioventral projections are small and of unequal length, the anterior ones are the smallest. All test projections are echinate. M1-M4 are continuous dorsally and ventrally; M5 is narrowly interupted ventrally. M2-M4 and M5-M6 are converged mid-dorsally over a short distance only. The stomach partly extends into the middle posterior projection.

Size
Length of aggregate zooids 1.8-18.2 mm. Length of solitary zooids 2.3-11.7 mm.

Depth range
Epipelagic, living in the upper 100 m, does not perform diurnal vertical migration.

Distribution in the North Sea
Possible occurring in the northern North Sea as a seasonal visitor.

World distribution
Cosmopolitan, eurythermic species from warmer waters; roughly occurring between ca. 60°N and ca. 40°S. Also present in the Mediterranean Sea.

Remark
In solitary zooids, the number of muscle fibres in M1-M6 shows clinal variation, decreasing from higher to lower latitudes, in other words, from colder to warmer waters (see Van Soest, 1975b). Shoals of T. democratica occurring off the Hebrides in July-August were reported by Sewell, 1953.

Kingdom Animalia
Phylum Chordata
Subphylum Tunicata
Class Thaliacea
Order Salpida
Family Salpidae
Subfamily Salpinae
Genus Thalia
Species Thalia democratica

Status in World Register of Marine Species

Accepted name: Thalia democratica (Forskål, 1775)

Scientific synonyms and common names

Salpa democratica | Forskål, 1775
Salpa mucronata | Forskål, 1775 (used for the solitary form)
Salpa spinosa | Otto, 1823
Dubreuillia cirrhosa | Lesson, 1830
Salpa caboti | Desor, 1848
Thalia democratica var. orientalis | Tokioka, 1937
Thalia democratica f. typica | Sewell, 1953
Thalia democratica ssp. democratica | Borgelt, 1968

Apstein, C., 1905. Salpen der deutsche Tiefsee-Expedition. Wissentschaftliche Ergebnisse der deutschen Tiefsee-Expedition auf dem Dampfer "Valdivia" 1898-1899, 12(3): 245-290 (7 plates). Fisher Verlag, Jena.

Bone, Q. (ed.), 1998. The biology of pelagic tunicates. Oxford University Press, Oxford. 340 pp.

Fraser, J.H., 1981. British pelagic tunicates. Synopses of the British Fauna (New Series), No. 20. Cambridge University Press, Cambridge. 57 pp.

Godeaux, J., 1998. The relationships and systematics of the Thaliacea, with keys for identification. In: Q. Bone (ed.), 1998. The biology of pelagic tunicates. Oxford University Press, Oxford. pp 273-294.

Sewell, R.B.S., 1953. The pelagic Tunicata. The John Murray Expedition 1933-34 Scientific Reports, Vol. 10, No. 1. British Museum Natural History, London. 90 pp.

Soest, R.W.M. van, 1973. The genus Thalia Blumenbach, 1798 (Tunicata, Thaliacea), with description of two new species. Beaufortia, 20(271): 193-212.

Soest, R.W.M. van, 1975b. Zoogeography and speciation in the Salpidae (Tunicata, Thaliacea). Beaufortia, 23(307): 181-215.

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