internal organs. As a result, parts of the very long gut
and the sex organs have had to migrate into the walking
legs. This sounds crazy, but in some species each of the
eight legs is more capacious than the body of the animal.
Overall their physique is strongly reminiscent of terrestrial spiders, hence their common name. However, their
scientific placement in zoological systematics remains a
matter of dispute.
Around 1,200 different pantopod species have been
scientifically described, and they all occur exclusively in
the sea. Their habitat ranges from shallow coastal zones
to the bottom of the sea up to a depth of 6,500 feet (
several thousand meters), and even in the Antarctic Ocean
they occur in an astonishing variety of forms. One of the
largest species known, a member of the genus
Colossend-eis, has been found there at 23,000 feet ( 7,000 m) and
is a true giant, with a width of an incredible 27½ inches
( 70 cm). However, the majority of species are appreciably
smaller and often don’t even attain 4 inches ( 10 cm).
The sea spider that turned up in my aquarium was
about 1 cm—less than ½ inch—across. I had no idea
whether or not it was already full-grown. It had light, almost white legs with reddish rings and a gray-beige body,
rather plain from a coloration point of view. The majority of species have camouflage coloration to conceal
them from predators. Some species amplify this effect by
camouflaging themselves with material from their surroundings, and even allow themselves to become overgrown with all sorts of life forms. However, there are also
splendidly colored pantopod species on the coral reefs,
and these, at least, would look beautiful in a reef aquarium. Unfortunately, many sea-spider species are predatory, and the specimens that are found on coral reefs
now and then are often parasites that feed on the tissues
of specific host animals, such as corals, hydroid polyps,
bryozoans, mollusks, and, in rare cases, sea cucumbers. A
number of species purportedly also feed on algae. Obviously, zooanthids featured on the menu of my specimen.
Sea Spider anatomy
top: denise nielsen tackett; bottom: m. Friedrich
On the sea spider’s head there is a proboscis with a
mouth opening at its tip; the mouth contains three little
teeth and is eminently suited to sucking fluid from the
tissues of the zooanthids. In order to study the creature
more closely and protect my much-prized Zoanthus colony, I captured it (child’s play, given its slow and rather
comical mode of movement) and fixed it for photography under my binocular microscope. A tiny, turret-like
structure was immediately visible on the head of the
creature: the ocular tubercle, which bears four simple,
inverted, single-lens eyes. One pair pointed forward, the
other backward—a very practical way to see in all directions and spot enemies. At the tip of each walking leg
there was a terminal claw with two ancillary claws at
its base, which provides a firm grip when the spider is
clambering around among the corals. Some species with
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