are separate in most species, though a few are hermaphroditic or protandric. The gonads are located in the disk, and open into pouches between the arms, called genital bursae. Fertilisation is external in most species, with the gametes being shed into the surrounding water through the bursal sacs. An exception is the Ophiocanopidae, in which the gonads do not open into bursae and are instead paired in a chain along the basal arm joints. Many species brood developing larvae in the bursae, effectively giving birth to live young. A few, such as Amphipholus squamata, are truly viviparous, with the embryo receiving nourishment from the mother through the wall of the bursa. However, some species do not brood their young, and instead have a free-swimming larval stage. Referred to as an ophiopluteus, these larvae have four pairs of rigid arms lined with cilia. They develop directly into an adult, without the attachment stage found in most starfish larvae. The number of species exhibiting ophiopluteus larvae are fewer than those that directly develop. In a few species, the female carries a dwarf male, clinging to it with the mouth. Fission Some brittle stars, such as the six-armed members of the family Ophiactidae, exhibit fissiparity (division through fission), with the disk splitting in half. Regrowth of both the lost part of the disk and the arms occur which yields an animal with three large arms and three small arms during the period of growth. The West Indian brittle star, Ophiocomella ophiactoides, frequently undergoes asexual reproduction by fission of the disk with subsequent regeneration of the arms. In both summer and winter, large numbers of individuals with three long arms and three short arms can be found. Other individuals have half a disk and only three arms. A study of the age range of the population indicates little recruitment and fission is the primary means of reproduction in this species. In this species, fission appears to start with the softening of one side of the disk and the initiation of a furrow. This deepens and widens until it extends across the disk and the animal splits in two. New arms begin to grow before the fission is complete, thus minimizing the time between possible successive divisions. The plane of fission varies so that some newly formed individuals have existing arms of different lengths. The time period between successive divisions is 89 days, so theoretically,