Family PYROSOMATIDAE

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Introduction

The family Pyrosomatidae Lahille, 1888, the only known family of the thaliacean order Pyrosomatida, contains species with free swimming tubular colonies of numerous zooids embedded in common transparent test, with their branchial (incurrent) apertures around the outside of the colony and the atrial (excurrent) apertures opening into the central (cloacal) cavity. The central cavity is open at the posterior end of the colony and the excurrent stream of water is forced out through this opening, creating the jet by which the colony is propelled through the water. The pharynx is perforated by numerous long, parallel stigmata, and the short gut loop is postero-ventral to it. The atrial chamber opens at the posterior end of the zooid. Luminous organs are on each side of the anterior end of the pharynx. A vegetative stolon is at the posterior end of the endostyle.

There are two subfamilies, Pyrosomatinae (Pyrosoma Péron, 1804 and Pyrosomella Van Soest, 1979) and Pyrostremmatinae (Pyrostremma Garstang, 1929). In the Pyrosomatinae replication is by isolation of a bud (from the tip of a vegetative stolon) which moves towards the open end of the colony. In the Pyrostremmatinae, the buds form in continuous chains from the stolon, and even after separation lie more or less in rows in the colony. Eggs are fertilised in situ in the parent zooid, and develop into rudimentary colonies before liberation from the parental common cloaca.

Pyrosomella differs from Pyrosoma in its strictly parallel rows of zooids. This genus has not been recorded from Australian waters although it is known in the tropical Indo-west Pacific. The order Pyrosomatida is reviewed by Neumann (1935) and Van Soest (1979, 1981). Thompson (1945) has reviewed the species recorded from Australian waters.

General References

Garstang, W. 1929. Tunicates. Encyclopedia Britannica 14: 549-555 [pubication date established from Van Soest, R.W.M. 1981. A monograph of the order Pyrosomatida (Tunicata, Thaliacea). Journal of Plankton Research 3(4): 603–631]

Lahille, F. 1888. Etude systématique des tuniciers. Comptes Rendus de l'Association Française pour l'Avancement des Sciences 1887(2): 667-677

Mueller, O.F. 1776. pp. 224–226 in, Zoologiae Danicae. Copenhagen : Prodromus.

Neumann, G. 1935. Thaliacea. pp. 203-500 in Kükenthal, W. & Krumbach, T. (eds). Handbuch der Zoologie. Berlin : Walter de Gruyter Vol. 5(2).

Péron, F. 1804. Mémoire sur le nouveau genre Pyrosoma. Annales du Muséum National d'Histoire Naturelle. Paris 4(12): 437-446 pl. lxxii

Thompson, H. 1945. Pelagic Tunicates of Australia. Melbourne : Council for Scientific and Industrial Research 196 pp. 75 pls.

Van Soest, R.W.M. 1979. Revised classification of the order Pyrosomatida (Tunicata, Thaliacea) with the description of a new genus. Steenstrupia 5(11): 197-217

Van Soest, R.W.M. 1981. A monograph of the order Pyrosomatida (Tunicata, Thaliacea). Journal of Plankton Research 3(4): 603-631

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