Morphological change due to growth found in Caprella equilibra Say

Abstract

Three developmental stages of Caprella equilibra Say have been studies - a young of 10 mm in body length, a semi-adult of 12mm and a full-grown of 22mm. In the young, the second antenna is longer than the peduncle of the first antenna, and in the fully grown, it is about 1/2 or 1/3 the length of the first antenna. This difference probabiy due to unusual growth of the second and third segments of the first antenna. The flagellum of the first antenna is consisted of 10 joints in the young, of 12 in the semi adult and of 18 in the fully grown. As she animal grows, the first and second segments grow excessively, so that the first segment attains almost twice as long as the third segment, and the second almost thrice the third. Lateral spines are growing in second, third, fourth and fifth segments. As the animal grows, the ratio between the length of hand and the whole body length decreases, but that between palmar tooth and palmar poison tooth increases. Such differences are peculiar to the aged individual of this species.