ophiura
Active Member
Thanks to SCOTTS and others for some motivation to write some of this up
And I'll count on many of you to provide pictures of your stars!
This is Part I on a series to cover Seastars and Brittlestars...perhaps someday their other relatives
Part I covers the "reef safe" seastars such as Linckia. Other parts will cover non reef safe stars, sand sifters, etc.
Google some of the bold faced terms for cool info.
[hr]
Guide to the ‘Stars: Seastar Care and Selection
There are several common classes of echinoderms (which means “spiny skin”) in the aquarium hobby. They include sea urchins (Echinoidea), sea cucumbers (Holothuroidea), brittlestars (Ophiuroidea) and seastars (Asteroidea). Less commonly seen and kept (for good reason) are the featherstars (Crinoidea).
Though these critters don’t look very similar at all, they are related. Clearly, searstars, urchins and brittlestars all have the “spiny skin” characteristic of the group. Sea cucumbers do not appear to have these spines, but that is because the skeleton is reduced, and embedded in the skin. Echinoderms have an internal skeleton composed of calcium carbonate, but they are still invertebrates. The skeleton is covered to a greater (eg sea cucumbers) or lesser (eg seastars) degree with a layer of living tissue. This prevents things from settling on the animal and growing there. Several classes have fascinating structures to deal with “fighting off” critters that may want to settle on them including the pedicellaria of urchins and some seastars.
Echinoderms also have pentamerous or “five part” symmetry, which is pretty clear in certain classes. This does not necessarily mean that all seastars must have 5 arms, however. There are exceptions to this. They have an internal hydraulic system called the water vascular system or WVS. The WVS includes the tube feet you see the animal using to move. This system is used in locomotion, feeding, respiration and excretion. An additional “cool fact” is that echinoderms possess a fascinating type of connective tissue called mutable collagenous tissue. It is extremely interesting to scientists because the animal can control the mechanical properties of this tissue at will. It can become extremely firm, so as to “lock” spines in place; it can become extremely weak, allowing the arms of brittlestars to not break, but literally fall off if threatened.
The specific purpose of this series for the Saltwaterfish.com forum is to cover seastars and brittlestars which, though they seem somewhat similar, are actually different classes of animals. There are several differences. Primarily the arms and central disk area of seastars are continuous whereas the central disk of brittlestars is very distinct from the arms. There are also anatomical differences in the tube feet, and movement in general.
We will start with covering a specific group of seastars. Seastars (aka “starfish”) are a very diverse group of around 1800 species. Of this only a small handful end up in our tanks, whether intentionally or otherwise. They exploit a diversity of feeding styles which is important to consider in selecting one. Will it eat corals? Will the fish I keep eat the seastar? Important questions to know. Additionally, water quality is critical to keeping ANY echinoderm healthy. They are especially sensitive to salinity fluctuations.
Google some of the bold faced terms for cool info.
[hr]
Guide to the ‘Stars: Seastar Care and Selection
There are several common classes of echinoderms (which means “spiny skin”) in the aquarium hobby. They include sea urchins (Echinoidea), sea cucumbers (Holothuroidea), brittlestars (Ophiuroidea) and seastars (Asteroidea). Less commonly seen and kept (for good reason) are the featherstars (Crinoidea).
Though these critters don’t look very similar at all, they are related. Clearly, searstars, urchins and brittlestars all have the “spiny skin” characteristic of the group. Sea cucumbers do not appear to have these spines, but that is because the skeleton is reduced, and embedded in the skin. Echinoderms have an internal skeleton composed of calcium carbonate, but they are still invertebrates. The skeleton is covered to a greater (eg sea cucumbers) or lesser (eg seastars) degree with a layer of living tissue. This prevents things from settling on the animal and growing there. Several classes have fascinating structures to deal with “fighting off” critters that may want to settle on them including the pedicellaria of urchins and some seastars.
Echinoderms also have pentamerous or “five part” symmetry, which is pretty clear in certain classes. This does not necessarily mean that all seastars must have 5 arms, however. There are exceptions to this. They have an internal hydraulic system called the water vascular system or WVS. The WVS includes the tube feet you see the animal using to move. This system is used in locomotion, feeding, respiration and excretion. An additional “cool fact” is that echinoderms possess a fascinating type of connective tissue called mutable collagenous tissue. It is extremely interesting to scientists because the animal can control the mechanical properties of this tissue at will. It can become extremely firm, so as to “lock” spines in place; it can become extremely weak, allowing the arms of brittlestars to not break, but literally fall off if threatened.
The specific purpose of this series for the Saltwaterfish.com forum is to cover seastars and brittlestars which, though they seem somewhat similar, are actually different classes of animals. There are several differences. Primarily the arms and central disk area of seastars are continuous whereas the central disk of brittlestars is very distinct from the arms. There are also anatomical differences in the tube feet, and movement in general.
We will start with covering a specific group of seastars. Seastars (aka “starfish”) are a very diverse group of around 1800 species. Of this only a small handful end up in our tanks, whether intentionally or otherwise. They exploit a diversity of feeding styles which is important to consider in selecting one. Will it eat corals? Will the fish I keep eat the seastar? Important questions to know. Additionally, water quality is critical to keeping ANY echinoderm healthy. They are especially sensitive to salinity fluctuations.