Crystal clear waters, a very nice and calm ocean were the propitious conditions we found today on the waters surrounding Bartolome Island. In our outings in the glass bottom boat, hundreds of colorful tropical fish were spotted, including a fairly large white-tipped reef shark. However, invertebrates like seastars and sea urchins, due to their peculiar shapes and abundance in these waters, rapidly captured the attention and became favorites of all.
In the picture taken today through the glass of the boat, we can fully appreciate one of these peculiar invertebrates, the white sea urchin (Tripneustes depressus). Like other sea urchins, it bears a spiny armament, this trait is essential for their namesake, echinoids. The latter name is derived from the Greek word echinos, meaning "hedgehog". The white sea urchin is the largest Galapagos sea urchin. It has an overall diameter of 16 cm (6.3 in). It is globose in shape and has short, almost white spines. It is very conspicuous and is often seen atop submerged boulders that are covered with algal tufts and algae, its principal foods. This echinoid prefers to live in areas of high water movement but not in areas of high turbulence. The white sea urchin is considered common in the Galapagos, but the population density varies considerably from place to place in the archipelago. It has a very wide distribution, it is found in the Pacific Ocean from southern California to Ecuador and its Galapagos Islands.
