This is a photo I took of a sea urchin displaying it’s anus. It’s unusual to catch them doing this, it’s usually at night and not very frequently at that. But here it is. The Urchin Anus photo is the main one. The Urchin Normal is what a sea urchin would normally look like. They have very sharp spines that are extremely brittle and will easily break off inside a wound. The spines are sharp enough to penetrate neoprene rubber etc. They are aware of your presence and will move the spines to point at an intruder and will actually follow a hand from side to side.
The bubble like thing on the top is part of their digestive tract. Their mouth is on the bottom and the anus is on the top. This is a common tropical urchin, genus Diadema. Here it is clearly displaying it’s everted anal sac which is used for gas exchange. While totally rude for any human to wave their anal sac around in the water, it’s common, and acceptable, for members of Diadema to evert their anal sacs.
Terry is a founding partner and scuba instructor for Aquatic Sports and Adventures (Deportes y Aventuras Acuáticas) in Manzanillo. A PADI (Professional Association of Dive Instructors) Master Instructor in his 36th year as a PADI Professional. He also holds 15 Specialty Instructor Course ratings. Terry held a US Coast Guard 50-Ton Masters (Captain's) License. In his past corporate life, he worked in computers from 1973 to 2005 from a computer operator to a project manager for companies including GE Capital Fleet Services and Target. From 2005 to 2008, he developed and oversaw delivery of training to Target's Loss Prevention (Asset Protection) employees on the West Coast, USA. He led a network of 80+ instructors, evaluated training, performed needs assessments and gathered feedback on the delivery of training, conducted training in Crisis Leadership and Non-Violent Crisis Intervention to Target executives. Independently, he has taught hundreds of hours of skills-based training in American Red Cross CPR, First Aid, SCUBA and sailing and managed a staff of Project Managers at LogicBay in the production of multi-media training and web sites in a fast-paced environment of artists, instructional designers, writers and developers, creating a variety of interactive training and support products for Fortune 1000 companies.