Fig. 12.
Chelyosoma macleayanum, slightly enlarged. a, branchial; b, atrial orifice.
The fine specimen of Phallusia mammillata from Naples consists of several individuals partly fused together; the branchial and atrial orifices are wide open, and the mantle can be seen through the thick knobby translucent test.
In Rhodosoma the test is modified so as to form stiff plates recalling the valves of a bivalve shell. One plate is attached to the rocks, the other closing against the first like a lid; the anterior end of the animal with its branchial and atrial orifices is visible only when the lid is open. The Mediterranean species R. callense (Fig. 13) grows attached to the rocks. The little exhibited specimen is on a fragment of shell in front of a black patch. The figure shows specimens with the lid open and closed.
Fig. 13.
Rhodosoma callense, × 10. A, “valve” open; B, shut. a, branchial; b, atrial orifice. (After Lacaze Duthiers.)
Family Clavelinidæ. The body is attached to a creeping stolon or mass of stolons, from which new individuals arise by budding. The other three families of Simple Ascidians included solitary forms, but the Clavelinidæ are social, and form colonies wherein each individual has its own test.
Clavelina lepadiformis (Fig. 14) forms graceful crystal vases about an inch in height. The figure shows one individual, but usually the processes at the base extend out as stolons whence other individuals arise.
Diazona violacea, from Cornwall, forms beautiful purple disk-shaped colonies in which the ascidiozooids arise from a basal mass of stolons. Sometimes the ascidiozooids die down, leaving only a smooth violet pad, which in due time produces a new crop of ascidiozooids.
Fig. 14.
Clavelina lepadiformis; diagrammatic, showing the anatomy. The oval bodies are the eggs; at lower end lies the tubular heart; the root-like processes at the base grow into stolons, whence other ascidiozooids arise.