NOVEL SKELETAL TOPOLOGIES ARE RELATED TO BIRTH IN ANTARCTIC SEA-URCHINS

The juveniles of two species of Antarctic holasteroid echinoids are pr otected in, and born from a unique brooding system contained within th e test of the female. This behavior represents the most extreme type o f parental care in the Echinoidea. The origin of the brooding system i s accompanied by dramatic changes in apical system architecture which can be resolved : 1) by comparing ocular and genital plate surface are a changes during ontogeny; 2) through shape analysis of sutural vertic es in the apex of males and females. We will discuss how these and oth er features might help explain the evolutionary derivation of the hola steroid brooding system from either: 1) complete innovation through mo dification of the ''ocular plate'' rule; 2) modification of pre-existi ng topologies found in other Eleutherozoa, but otherwise not strongly expressed in echinoids.