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The morphology and life history of a strange and unidentified botryllid ascidian were investigated. This ascidian was first collected from the stony shore of Ebisu Island in Shimoda. a city on Izu peninsula in central Japan. Unlike other botryllid ascidians. whose colonies are flat and smooth, this ascidian's colonies are rugged. In each colony, zooids are arranged into several oval systems, each of which has a thick part containing zooids and very thin parts that do not. The arrangement of ovary and testis in this species is the same as in other species of the genus Botryllus; the ovary is situated anterior to the testis, The embryo of this ascidian develops in the peribranchial cavity of its mother zooid without any brooding organs, as is the case with Botryllus scalaris and Botryllus puniceus. Meanwhile, the results of cut colony assay experiments did not show the existence of colony specificity in this ascidian, Even when two syngeneic colonies were brought into contact a! their growing edges, none fused together. On the other hand, when two colonies were brought into contact with each other at their cut surfaces, they always fused into a single colony, regardless of their origin. Therefore, this species may be the only species that lacks colony specificity among the botryllids studied so far. [ABSTRACT FROM AUTHOR]

The morphology and life history of a new species of the genus Botryllus belonging to the family Botryllidae are described in detail This ascidian was collected from the stony shore in the cove near Shimoda Marine Research Center, University of Tsukuba (Shimoda, Shizuoka Prefecture, Japan). The ascidian colony was easily distinguished from colonies of other botryllids because it was very thin and bright pink in color. The arrangement of ovary and testis in this ascidian was the same as that in other species of the genus Botryllus. This ascidian was prolific, with 1-5 embryos on each side of a zooid. and the embryos of this ascidian developed in the peribranchial cavity without any brooding organs as in Botryllus scalaris. We observed the processes and features of the allorecognition reaction in colony specificity and found that allorejection occurred after fusion of the vascular system between two incompatible colonies. This manner of allorejection is also shown in B. scalaris and Botryllus delicatus; however, the reaction speed of allorejection is faster than that of B. delicatus and similar to that of B. scalaris. These results indicate that this ascidian might be closely related to B. scalaris. [ABSTRACT FROM AUTHOR]