There is a figure of eight shaped ring of small papillae around the aboral tip. On surfaces, they move laterally, with the aboral surface facing the substrate. The aboral (upper) surface is clothed in groups of short, blunt spines. The aboral or upper surface has a patchwork of closely packed spiny plates. The aboral face is often covered with tiny spines looking like paxillae. Planula larvae swim with the aboral end (the end opposite the mouth) in front. Others, such as certain Euryalina, have one per arm on the aboral surface. On the upper or aboral surface of the disc is an opening, the madreporite. It has a solid but slightly rounded aboral (upper) surface. Differentiation occurs near the aboral pore and this is where most neurons remain.