The hand of dusk

Another one of my alien space creatures! This one's a crinoid, which are my favourite type of echinoderm.

This is the creature I wanted help with earlier, it still looks pretty much like a crinoid but at least now there are a few other animals contributing to its' anatomy.

And now to the sciency description! it's been too long since I wrote a good creature bio like this.

Common name: Whisker star

Latin name: Tenebra pugnus

Family: Astercrinidae (Star lilys)

Physiology: Although the external morphology of these crinoids has not altered that much upon their adaptation to space, internally they are extremely different to their marine ancestors. To start with, the hydrostatic water vascular system has been largely replaced with the haemal system, although a remnant of the system is still used to operate the tube feet in the arms. They still don't have a heart though, so the nutrient containing fluid in the haemal system is pumped around the body by the constant swaying of the stalk, which makes them look as if they are being moved by non-existent currents.

However, this swaying is not sufficient to move it round the body fast enough to supply all the cells with nutrients, so the looped intestine instead of being restricted to the calyx (the main body to which the arms are attached) runs all the way down the stalk, providing nutrients to the connective tissue directly.

They are hugely variable in size, newly metamorphosed adults are typically 1-2 metres high, but given favourable conditions there seems to be no upper limit to their size, since there is no danger of collapsing under their own weight in the vacuum of space.

They have a de-centralised nervous system which means that instead of having one brain, they have several specialised nerve clusters scattered around their bodies. None of these clusters is particularly sophisticated, but they work well enough for it to function.

At the base of the stem tentacle-like cirri act as a holdfast securing it to the asteroid chosen as its' substrate, they are capable of letting go but due to the scarcity of suitable locations and the fact that without things to push against they are incapable of moving this is extremely unlikely. The cirri also function almost as the lungs of the animal, with millions of pores through which corrosive digestive juices are extruded to break down the rock, special fleshy chambers just below the loop of the intestine act as reaction vessels to release the oxygen stored in inorganic oxides.

Description: Their outward appearance is roughly similar to marine crinoids, with a calcareous exoskeleton, long stalk and pentaradial symmetry. The five arms are biramous, split into two parts to better entangle prey, and have rows of interlocking armour plates that serve as teeth, the arms can 'bite' and tear off chunks of flesh while the victim is still struggling, the tube feet within the arms act as a sort of tongue and pass the food down to the mouth at the centre. For every arm there is a whisker-like protrusion suspected to be derived from the pinnules found on the arms of marine crinoids. These are extremely sensitive, and act as combined touch-taste receptors, although the primary sense is touch, chemical traces are used to orientate the crinoid so that it 'faces' the direction the potential prey is approaching from.

Behaviour: Their behaviour is limited, being sessile with a diffuse nerve network instead of a true brain makes them rather simple behaviourally. They are still deadly ambush predators though, grabbing and killing anything that comes within reach.

They have separate male and female individuals, however due to the difficulty of finding the opposite sex in the vastness of space (especially if you're sessile and can't move) the males don't become adults until they find a mature female, they remain drifting until the pheremones she releases triggers metamorphosis. Female larvae metamorphose when they encounter any solid object they can cling to, so solitary individuals are always female, and in a cluster the largest will be the female and all the smaller individuals males.

Males release spermatophores (packages of sperm) which the female collects and uses to fertilise her eggs, the newly hatched larvae are brooded in the base of her whiskers, the whiskers themselves are retracted and digested to provide foo for the developing young, so it is rare for a female to eat at all while looking after her young. Once they are ready the larvae are released en mass, they have sheet-like 'wings' which allow them to use light to propel themselves through the blackness in search of a place to settle.

Notes: These creatures are a serious navigational hazard to ships, their stalks are extendable by quite a surprising distance and they are either unable to tell the difference between flesh and blood animals and spaceships or indifferent, and their exoskeletons are strengthened by the materials extracted from the rock, so some individuals are capable of breaking through weak hulls.