Biology/Natural History: Ascidia paratropa
probably breeds only in the summer, and it does not brood its eggs. Its diploid chromosomes complement is 18. It can be hybridized experimentally with A. callosa.
The egg envelopes must be removed manually (digesting them off with the enzyme trypsin drastically upsets development). With this precaution about two-thirds of A. callosa
eggs and one-half of A. paratropa
eggs fertilized by the other species develop into only slightly distorted tadpoles; a few settle and metamorphose to zooids that appear functionally competent except for aberrant guts. An attempt to raise offspring through sexual maturity has not been made yet. The tunic of A. paratropa
, glasslike in its transparency, has received some study. It is very largely sea water, the organic matter constituting only .8 percent of tunic wet weight. About half the organic matter is carbohydrate resembling plant cellulose, and about half is protein. Investigation of the brain of A. paratropa
shows the presence of neurosecretory cells of the sort characteristic of the Ascidian suborders Aplousobranchia