Pentacula | devbiopparvimensis

Pentacula

      After doliolaria, Parastichopus parvimensis metamorphose into pentacula. There is no metamorphosis or drastic change in body plan after pentacula. From pentacula, the sea cucumbers progress to their juvenile adult form.
     The major change that marks metamorphosis is when the buckle tentacles break through the anterior end, and the sea cucumber goes from swimming in the water column to walking along the substrate. At this point, the buckle tentacles have enlarged and become a dominant feature. Simultaneously, a tube foot begins to grow out the side of the cucumber, towards the posterior end (Figure 1). The sea cucumber uses this tube foot to attach to the substrate.
       Figure 1 and Video 1 depict a recently metamorphosed pentacula. The 5 ciliary bands from doliolaria are still present and the cilia can be seen flapping. It seems that the awkward tube foot is not yet functioning.

       After these changes, the pentacula slowly gains its adult characteristics. The ciliary bands disappear completely, and spines begin to cover the epidermis. Distinct skeletal structures can be seen forming at the base of each spine (Figure 2). Eventually, more tube feet start to grow on the ventral side of the pentacula.
       Upon metamorphosis, bilateral symmetry becomes pentaradial symmetry, characteristic of echinoderms. Although the pentaradial symmetry is not as conspicuous as it is in asteroids, sea cucumbers have the same five ambulacrum – three usually located on the ventral side, side with the tube feet, and two on the dorsal side. Additionally, the anterior posterior axis becomes the anterior posterior axis respectively. See Body Plan for more information.
       Metamorphosed pentacula are about the cutest larvae you will ever see in your life. They walk around unevenly on their five buckle tentacles and wave their awkward tube foot around in the air. When they find something delicious to eat, such as a piece of detritus, they grab it and stick their whole buckle tentacle in their mouth. When they are young, it is not uncommon to a pentacula with all of its buckle tentacles stuffed inside its mouth (Figure 3).

Figure 1: Early Pentacula - numbers indicate ciliary bands from doliolaria

Video 1: Early Pentacula

Figure 2: Pentacula with Labeled Body Parts

Figure 3: Pentacula with Buckle Tentacles stuffed inside mouth

Video 2: Awkward Pentacula