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Butterfly Crabs
Topic Started: Jul 16 2008, 01:49 PM (2,324 Views)
Livyatan


The butterfly crabs are among the most successful animal groups on Tethys. They consist of several dozen orders of species from flatmoths to crabwhales. They occupy many niches including predators, scavengers and detritivores, filter-feeders (like whale sharks), and algae-eating browsers. Butterfly crabs range in size from a mere inch (flatmoths and scuttlelobsters) to nearly ninety feet in length (crabwhales). Even with such ecological diversity and immense evolutionary success, they all are quite similar in body plan having achieved a perfection similar to that of the crocodilians on Earth, being able to be great adapters while still maintaining the essence of a basic body plan.

Anatomy

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Butterfly crabs and their relatives are basically similar to Terran arthropods. They have segmented bodies and jointed appendages as well as strong exoskeletons. The exoskeleton is leathery and quite flexible as opposed to how it appears. All butterfly crabs share the same basic external anatomy, the main differences being the length and shape of limbs, the shape of the thoracic segments, length of the pygidium, size of eyes, etc. One of the key differences between butterfly crabs and the arthropods of Earth is how the antennae evolved: on Tethys II, the antennae of butterfly crabs evolved from hypersensitive, elongated mouthparts. Overtime they lost their use in feeding, but became important sensory devices.

Flatmoths
Flatmoths are perhaps the most basal of all butterfly crabs, conforming the most to the basic butterfly crab anatomy (pictured above). Like all species they have two pairs of eyes, one pair facing forward and to the side of the mouthparts and the other on top of the head segment, looking above. They mostly dwell at the seafloor or in tidepools, feeding on dead life or hunting for themselves. Not only are the most basal butterfly crabs, but they are also the smallest, ranging in size from an inch to about six or seven inches. Most have very dull coloration, which they use as camouflage to blend in with sand, etc.

Scuttlelobsters/Scuttlecrabs
Scuttlelobsters, or scuttlecrabs, are another group of butterfly crabs known for their minuscule sizes. A majority of the species are only about one to three inches in carapace length, although several species may reach upwards of five feet. They are highly distinct from other butterfly crabs with their unusually rounded exoskeleton, extremely elongated legs, and shortened pygidium. Their long legs are used as a height advantage, enabling them to see further and have a better view whilst foraging. The abyssal stiltwalkers, the largest of the scuttlelobsters, can be found in the deeper parts of Tethyian seas, dwelling alongside other giants such as the giant tongueworm.

Grazercrabs/Algal crabs
More information on grazercrabs coming soon.

Snapper crabs
More information on snapper crabs coming soon.

Waspcrabs
The waspcrabs, or seawasps, are a group of mostly predatory butterfly crabs. Although many find it advantageous to be camouflaged, there are several species that are well known for their striking and bizarre coloration, most likely used for reproductive display. Ecologically, they are the sharks and seals of Tethyian seas, but they also share predatory roles with eelworms and other fish-like worms. The spine at the end of its tail segment is not much of weapon, used mostly for defense or display. The extremely extended third set of legs is used like claspers, to keep its mate under control during copulation. These extended limbs are also present in the closely related wingheads, a smaller family of more obscure creatures.
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Common seawasp

Wingheads
The wingheads are a poorly described group of butterfly crabs that are related to the waspcrabs as previously mentioned. Their most distinctive features are their wide head segments, long third legs (which end in suction-cup like pads), and a sharp spine. Unique to the wingheads, their spines are highly poisonous. The spines are in fact so poisonous that they may kill as quickly as a few minutes. Some other species of butterfly crabs have evolved spine-like tips to their pygidiums and wider heads in order to mimic wingheads and hopefully scare off predators. Wingheads are much smaller than seawasps, reaching anywhere from four inches to three feet, while seawasps range from six inches to 28 feet.
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Tiny winghead

Flatrays
Flatrays are another group closely related to the seawasps. They differ from seawasps by having extremely flattened exoskeletons, small spines on its carapace, and much larger antennae. Flatrays are predatory much like their relatives, most being ambush predators. They hunt much like wobbegongs, hiding beneath the sand, using their antennae to sense when prey animals swim by.

Sandsifters
More information on sandsifters coming soon.

Crabwhales
More information on crabwhales coming soon.
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Spotted crabwhale
Edited by Livyatan, Jul 20 2008, 01:25 PM.
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PousazPower
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Technically, a pygidium is a terminal body region with the anus/cloaca on the end, so in this case, the "pygidium" would be a telson, because there's no gut in it (or if there is, it doesn't terminate there).
Was your nose discovered or invented?

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Livyatan


PousazPower
Jul 16 2008, 02:24 PM
Technically, a pygidium is a terminal body region with the anus/cloaca on the end, so in this case, the "pygidium" would be a telson, because there's no gut in it (or if there is, it doesn't terminate there).
Well technically its not Terran anatomy so the definition of the different parts may be different.
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PousazPower
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Are the mouthparts modified legs like in Terran arthropods, or did they evolve from something else?
Was your nose discovered or invented?

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Livyatan


No they did not. The mandibles actually evolved long before life became similar to arthropods. Many of the major classes in Tethys are descended from a group of small segmented worm-like creatures with tooth-like projections around their mouths. In eelworms, parrotworms, etc. these became their four mandibles (which actually function more like the beak of a bird). In butterfly crabs they became arthropod-like mouthparts. I'll have a cladogram for butterfly crabs pretty soon with some more insight into their ancestors.

Quick question: the common ancestor of these major groups only has one set of eyes, so is it possible for creatures with two sets of eyes to evolve from one-eyed ancestors?
Edited by Livyatan, Jul 16 2008, 04:15 PM.
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Sliver Slave
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I'm going back to basics.

Oh, you, teasing with that crabwhale picture.

Also, I need a decent imperial to metric calculator. These "feet" and "inches" are confuzzling me.
Edited by Sliver Slave, Jul 16 2008, 04:38 PM.
Something is upsetting the ostriches.

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PousazPower
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Jul 16 2008, 04:13 PM
Quick question: the common ancestor of these major groups only has one set of eyes, so is it possible for creatures with two sets of eyes to evolve from one-eyed ancestors?
Certainly! The eyes of spiders are actually individual facets of the ancestral chelicerate lateral eyes that have expanded to become something like giant ocelli, which, in some cases, are capable of forming images. So if the ancestral eyes were compound, then they could split into as many different eyes as there are ommatidia. Something else from the Holy Tome of Invertebrate Zoology: "The anterior lateral eyes, posterior medians, and posterior laterals are secondary eyes. These indirect eyes are thought to have derived from the lateral compound eyes of the ancestral chelicerate, although they no longer retain the faceted construction of typical compound eyes."

This has also happened in vertebrates, namely the four-eyed fish (Anableps sp.) Although the eyes aren't totally separate, I'm assuming they could be completely bifurcated in the near future.
Was your nose discovered or invented?

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Cynovolans
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Sliver Slave
Jul 16 2008, 04:38 PM
Oh, you, teasing with that crabwhale picture.

Also, I need a decent imperial to metric calculator. These "feet" and "inches" are confuzzling me.
I believe one foot is 30 cm, and 1 inch is 1.5 cm. BY the way, those are cool! Especially the waspcrab.
Edited by Cynovolans, Jul 16 2008, 05:53 PM.
I wish I could give the public a true picture of the queen as she appeared at her best, but this would be impossible, even had she permitted a photograph to be taken, for her charming play of expression while in conversation, the character and intellect which were then revealed, were only half seen when the face was in repose. -Lilias Underwood when speaking of Empress Myeongseong

"I was born in the dark. I went out into the light, and your Majesty, it is my displeasure to inform you that I have returned to the dark. I envision a Seoul of towering buildings filled with Western establishments that will place herself back above the Japanese barbarians. Great things lie ahead for the Kingdom, great things. We must take action, your Majesty, without hesitation, to further modernize this still ancient kingdom."-Min Young-ik to Empress Myeongseong
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Livyatan


Just so you all know there are several more groups of butterfly crabs, including: sandsifters, algal crabs, turtlecrabs, etc. Algal crabs and turtlecrabs are unique among butterfly crabs by being the only herbivores. Sandsifters are a more basal group related to the immense crabwhales. A sister group to the butterfly crabs that I have yet to design will consist of zooplankton like creatures. The larvae of true butterfly crabs, sparrowworms, and tongueworms will also be members of the Tethyian zooplankton.
Edited by Livyatan, Jul 16 2008, 06:16 PM.
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Saxophlutist
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I like what you've done here.
Despite the outward arthropod-like appearance, I would guess that these guys would be the "vertebrates" of your planet?
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Livyatan


Saxophlutist
Jul 16 2008, 06:34 PM
I like what you've done here.
Despite the outward arthropod-like appearance, I would guess that these guys would be the "vertebrates" of your planet?
There are no "vertebrates" on Tethys. The closest things to vertebrates would be sparrowworms and relatives, although that lack an internal skeleton. Actually there internal anatomy is set up more like annelids, but that is a whole different group. Butterfly crabs, on the other hand, are actually as similar to arthropods as their outward appearance suggests.
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Saxophlutist
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Well, what I meant by that ["vertebrates"] is, that they are the dominant macro-faunal organisms on your planet? In turn, making them effective vertebrate analogues. (Sorry for not phrasing it better :) )

Somewhat in the same way I refer to my "Sagitta" infraphylum as Europa's vertebrate analogues. (Though they are somewhat more like echinoderms, but only negligibly)
Edited by Saxophlutist, Jul 16 2008, 07:07 PM.
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Livyatan


Saxophlutist
Jul 16 2008, 07:04 PM
Well, what I meant by that ["vertebrates"] is, that they are the dominant macro-faunal organisms on your planet? In turn, making them effective vertebrate analogues. (Sorry for not phrasing it better :) )

Somewhat in the same way I refer to my "Sagitta" infraphylum as Europa's vertebrate analogues. (Though they are somewhat more like echinoderms, but only negligibly)
There isn't a single major faunal group that could be identified as the 'vertebrates'. All species are pretty much 'invertebrates'.
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Cynovolans
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I wish these were real, I would like to keep some of them in an aquarium.
I wish I could give the public a true picture of the queen as she appeared at her best, but this would be impossible, even had she permitted a photograph to be taken, for her charming play of expression while in conversation, the character and intellect which were then revealed, were only half seen when the face was in repose. -Lilias Underwood when speaking of Empress Myeongseong

"I was born in the dark. I went out into the light, and your Majesty, it is my displeasure to inform you that I have returned to the dark. I envision a Seoul of towering buildings filled with Western establishments that will place herself back above the Japanese barbarians. Great things lie ahead for the Kingdom, great things. We must take action, your Majesty, without hesitation, to further modernize this still ancient kingdom."-Min Young-ik to Empress Myeongseong
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Saxophlutist
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Paleognath
Jul 16 2008, 07:14 PM
Saxophlutist
Jul 16 2008, 07:04 PM
Well, what I meant by that ["vertebrates"] is, that they are the dominant macro-faunal organisms on your planet? In turn, making them effective vertebrate analogues. (Sorry for not phrasing it better :) )

Somewhat in the same way I refer to my "Sagitta" infraphylum as Europa's vertebrate analogues. (Though they are somewhat more like echinoderms, but only negligibly)
There isn't a single major faunal group that could be identified as the 'vertebrates'. All species are pretty much 'invertebrates'.
That's actually very good! :D It means you are able to move away from terrestrial analogues.

I mostly was able to do that, except some of my organisms seem to Cnideria-esque.
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