Crinoid

Saw this Crinoid spawning during a night dive. First time to see this after 12 years of diving. The tiny pink stuff are the eggs/sperm (spawn). The black thing 'sitting' on the coral is the Crinoid. Our dive lights attracted small shrimps and they were following us during our dives and when we shine our lights on this spawning Crinoid, it looks like the small Shrimps are feeding on them. Please watch the video to fully appreciates this Spotting.

Crinoids are marine animals that make up the class Crinoidea of the echinoderms (phylum Echinodermata). Crinoidea comes from the Greek word krinon, "a lily", and eidos, "form".

Crinoids are characterised by a mouth on the top surface that is surrounded by feeding arms. They have a U-shaped gut, and their anus is located next to the mouth. Although the basic echinoderm pattern of fivefold symmetry can be recognised, most crinoids have many more than five arms. Crinoids usually have a stem used to attach themselves to a substrate, but many live attached only as juveniles and become free-swimming as adults.

There are only about 600 extant crinoid species, but they were much more abundant and diverse in the past. Some thick limestone beds dating to the mid- to late-Paleozoic are almost entirely made up of disarticulated crinoid fragments.

Crinoids are dioecious, with separate male and female individuals. They have no true gonads, producing their gametes from genital canals found inside some of the pinnules. The pinnules eventually rupture to release the sperm and eggs into the surrounding sea water. The fertilised eggs hatch to release a free-swimming vitellaria larva. The larva is barrel-shaped with rings of cilia running round the body, and a tuft of sensory hairs at the upper pole. In some cases females have been known to temporarily brood the larvae using chambers within the arms. While both feeding and non-feeding larvae exist among the four other extant echinoderm classes, all present day crinoids appears to be descendants from a surviving clade that went through a bottleneck after the Permian extinction, which had lost its feeding larval stage. The larva's free-swimming period lasts only for a few days before settling to the bottom and attaching itself to the underlying surface using an adhesive gland on its ventral surface. The larva then metamorphoses into a stalked juvenile. Even the free-swimming feather stars sometimes go through this stage, with the adult eventually breaking away from the stalk. Within 10 to 16 months the crinoid will be able to reproduce.