All species of sorberaceans are solitary. Body shape is rather constant, Asajirus species almost always have an oval or egg-shaped body, and Oligotrema species are usually slightly more elongated and the siphons are situated on opposite ends of the body and directed away from each other. The test, a protective layer secreted by epithelium, is covered by short hairlike processes with adhering sand, mud particles, or, more often, tests of foraminiferans. The cloacal siphon is always small and inconspicuous. The branchial siphon is large, situated on the anterior end or on a side of the body, and surrounded by six large lobes. The opening of the branchial siphon leads to the buccal cavity lined with the test; the buccal cavity is homologous to the branchial siphon of other as-cidians. As in all tunicates, The pharynx is perforated, but unlike in other ascidians, is small and has only a few openings leading to a system of thin-walled chambers that open into the atrial cavity by ciliated stigmata. Some species have a very large globular stomach, which occupies most of the internal space of the animal. All species have a kidney, a large thin-walled excretory organ, similar to the kidney of ascidi-ans in the family Molgulidae (suggesting a possible relationship with this family).
All Hexacrobylidae are relatively small, from less than 1 in (3 mm) up to 2.4 in (6 cm), but usually they are usually no more than 1.4 in (1 cm) in greatest dimension.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.