REPRODUCTION, DEVELOPMENT AND POPULATION BIOLOGY OF THE CARIBBEAN OPHIUROID OPHIONEREIS-OLIVACEA, A PROTANDRIC HERMAPHRODITE THAT BROODS ITS YOUNG

Reproduction and development of the ophiuroid Ophionereis olivacea H. L. Clark, a species that broods its young, were investigated in Florida from January through December 1985 and in Belize in June 1985 and April 1986. O. olivacea has a maximum disc diameter of 5.2 mm and is a protandric hermaphrodite. Sex reversal occurs at disc diameters ranging between 2.2 and 4.0 mm; it has 400-mu-m diameter oocytes and is ovoviviparous. As expected from an obligate out-crosser, this ophiuroid has a similar allocation to male and female reproduction, in terms of gonad volume. Reproduction of the Florida population was monitored for one year. O. olivacea is a sequential brooder and incubates its young during the coldest months of the year. The females produce a single clutch of juveniles each year. Spawning starts in November and peaks in January and February. The ova are spawned synchronously from all the ovaries of each female into the bursae and are retained there. Fertilization is accomplished by intake of sperm into the female bursae. O. olivacea develops through a ciliated embryonic stage that appears to be a modified vitellaria larva lacking ciliary bands. These modified larvae swim in seawater in the bursae. Direct development in this species has resulted from heterochrony in the loss of ophiopluteus features. The number of brooding females in the population increases in November and reaches a maximum in March. Juvenile O. olivacea emerge from the bursae at a disc diameter of 480-mu-m and each arm has three segments. Recruitment was first detected in April, and juveniles were particularly abundant in June. Small size in O. olivacea is associated with paedomorphic heterochrony with precocious maturation of the males at a disc diameter of 1.5 mm, approximately 2 mo after taking up their free existence. Brooding as a life history mode in O. olivacea is examined and the adaptations of this species to its warm-water habitats are discussed.