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Thalia democratica


Brook Anderson (2013)     


Fact Sheet



Physical Description

Sexual Form

Asexual Form


Biogeographical Location

Feeding Ecology

Life History & Behaviour

Asexual Reproduction

Sexual Reproduction

Anatomy & Physiology

Sensory System

Muscular System

Feeding Structures and Function

Evolution & Systematics

Conservation & Threats

References & Links


The asexual individual (oozoid) is solitary and free swimming. The body appears elongate cylindrical and reaches a size of 2.3 –11.7mm in length (Davies and Slotwinski, 2012). A smooth test surrounds the body of the animal and is ventrally thickened. Water flow through the animal is directed through an anterior, incurrent buccal aperture, situated terminally and an excurrent atrial aperture, situated posterior-dorsally. 

The body is supported by 5 complete circular muscles inseries from M1 (anterior) to M5 (posterior) (fig 1). Muscles M1 – M3 and M4 – M5 may be mid-dorsally fused for a short distance. Two short lateral and two long posterior projections protrude as part of the test from the body. An atrial opening also protrudes from the posterior end, which encloses the nucleus. The nucleus contains the stomach and intestine. A stolon of developing zooids, if present, is coiled around and attached to the nucleus where its development occurs.

Located on the anterio-dorsal surface of the animal is asmall circular eye spot, on which the dorsal ganglion is situated. Directly anterior to this spot is the dorsal tubercle (fig 1). Due to the transparency of the animals, an internal dorsal lamina is evident running along theanterior-posterior axis of the body from the eye spot to the posterior nucleus. An endostyle is also present ventral to the dorsal lamina running along the anterior – posterior axis, terminating mid dorsally.