Our sea cucumber larvae have been developing beautifully.
Gastrulation is the process of forming an animals tissue layers. It is usually the first noticeable sign of an animal forming it's body axes. This is the early "gastrula" of a warty sea cucumber. The tube in the middle of the larva is the larval gut, and the place that the tube contacts the outside will be the larval anus.
This is a later gastrula. The tube on the short bottom of the larva is the forming gut, and the divot on the long side of the larva is where the top of the gut tube will contact the outside layer of the larva and the mouth will form.
These warty sea cucumber larvae are old enough to feed. Each larva has an oral hood (shaped like a star trek badge) and a lobe on the posterior (shaped like a keyhole). The flickering you may see in the thickenings around the margins of the animal and the oral hood are cilia in the ciliary band, which the larva uses to swim and capture algae to eat. Below the upside-down tear-drop shaped mouth (partially under the oral hood) you will see a tube (the esophagus) leading to a bulb shaped stomach. The anus opens on the posterior lobe, making the whole gut curved.
