# Are there any pentapod creatures? **URL:** \ **Category:** Factual Questions\ **Created:** [June 11, 2010, 2:12am UTC](https://boards.straightdope.com/t/are-there-any-pentapod-creatures/542736 "2010-06-11T02:12:31Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [June 11, 2010, 2:12am UTC](https://boards.straightdope.com/t/are-there-any-pentapod-creatures/542736/1 "2010-06-11T02:12:31Z")
And if not, why not? As someone who is vaguely familiar with evolution, I will gladly accept the answer “just cuz.” I remember reading somewhere about turn of the century German biologists writing about _Bauplan_,\* on the general morphology of animals, and a beautiful book by a Brit called Young or Thomas\* on similar themes (even suggesting, in retrospect, some themes of fractal growth. But I can’t remember anything on pentapods. \*Cite? ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [June 11, 2010, 2:20am UTC](https://boards.straightdope.com/t/are-there-any-pentapod-creatures/542736/2 "2010-06-11T02:20:31Z")
Seastars often have five limbs, is that what you mean? Most living creatures have symmetry. Either _bilateral_ or _radial._ Almost all animals are _bilateral_. Even the echinoderms start out as bilateral, even though adult echinoderms possess pentaradial, or five-sided, symmetry. So, I guess that’s what you are looking for? Some monkeys possess prehensile tails, giving them a “5th limb” of sorts. ---
**Author:** ![Silver\_Tyger](https://avatars.discourse-cdn.com/v4/letter/s/fbc32d/32.png) [@Silver\_Tyger](https://boards.straightdope.com/u/Silver_Tyger)\ **Post date:** [June 11, 2010, 2:20am UTC](https://boards.straightdope.com/t/are-there-any-pentapod-creatures/542736/3 "2010-06-11T02:20:48Z")
Starfish? ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [June 11, 2010, 2:32am UTC](https://boards.straightdope.com/t/are-there-any-pentapod-creatures/542736/4 "2010-06-11T02:32:09Z")
Thank you for your quick reply. > [@DrDeth](#): > > Seastars often have five limbs, is that what you mean? > > \*Most living creatures have symmetry. Either bilateral or \*\*radial. Almost all animals are \*\*bilateral. \* > > That’s what hung me up. > > Even the echinoderms start out as bilateral, even though adult echinoderms possess pentaradial, or five-sided, symmetry. > > Weird > > So, I guess that’s what you are looking for? > > Some monkeys possess prehensile tails, giving them a “5th limb” of sorts. This is fascinating. Mammal and all that. Why do you think pentapods are so rare on dry land compared to the sea? (Thanks Tyger Girl, also) ---
**Author:** ![ChrisBooth12](https://avatars.discourse-cdn.com/v4/letter/c/e95f7d/32.png) [@ChrisBooth12](https://boards.straightdope.com/u/ChrisBooth12)\ **Post date:** [June 11, 2010, 2:46am UTC](https://boards.straightdope.com/t/are-there-any-pentapod-creatures/542736/5 "2010-06-11T02:46:35Z")
Biology likes even numbers ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [June 11, 2010, 1:13pm UTC](https://boards.straightdope.com/t/are-there-any-pentapod-creatures/542736/6 "2010-06-11T13:13:33Z")
Not only starfish – echinoderms in general\* have five-fold symmetry, including crinoids and sea urchins: > [@](#): > > Special forms of radial symmetry > > Tetramerism: Many jellyfish have four radial canals and thus exhibit tetramerous radial symmetry. > > Pentamerism: > A sea urchin > A sea urchin > > This variant of radial symmetry (also called pentaradial and pentagonal symmetry) arranges roughly equal parts around a central axis at orientations of 72° apart. Members of the phyla echinodermata (like starfish) arrange parts around the axis of the forms. Examples include the Pentaspheridae, the Pentinastrum group of genera in the Euchitoniidae, and Cicorrhegma (Circoporidae). Like other echinoderms, sea urchins have five-fold symmetry (pentamerism). The pentamerous symmetry is not obvious at a casual glance, but is easily seen in the dried shell of the urchin. Flowering plants demonstrate symmetry of five more frequently than any other form. > > Around 1510–1516 C.E., Leonardo da Vinci determined that in many plants a sixth leaf stands above the first. This arrangement later became known as 2/5 phyllotaxy, a system where repetitions of five leaves occur in two turns of the axis. This is the most common of all patterns of leaf arrangement. > **[Symmetry (biology) - New World Encyclopedia](http://www.newworldencyclopedia.org/entry/Symmetry_%28biology%29)** \*although not invariably. Some are bilateral ---
**Author:** ![Giles](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/giles/32/60_2.png) [@Giles](https://boards.straightdope.com/u/Giles)\ **Post date:** [June 11, 2010, 1:35pm UTC](https://boards.straightdope.com/t/are-there-any-pentapod-creatures/542736/7 "2010-06-11T13:35:23Z")
The closest land animals are the macropods (kangaroos and wallabies). Their tail acts as a third leg when they are standing, or travelling fast, but they can use their arms as legs, as in [this picture](http://en.wikipedia.org/wiki/File:Red-Kangaroo-5legs.jpg). The description in the Wiki article on [Macropods](http://en.wikipedia.org/wiki/Macropods) says: > [@](#): > > Five ‘legs’ for moving slowly while browsing: the forelimbs and muscular tail take the animal’s weight while the hind legs are brought forward. ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [June 11, 2010, 2:25pm UTC](https://boards.straightdope.com/t/are-there-any-pentapod-creatures/542736/8 "2010-06-11T14:25:32Z")
> [@Leo\_Bloom](#): > > Thank you for your quick reply. > > This is fascinating. Mammal and all that. > > Why do you think pentapods are so rare on dry land compared to the sea? Because there aren’t any radially symettrical land animals. Most of the radial animals are sessile, which means they are filter feeders of some kind or another. But that doesn’t work on land, you can’t just pump air through your feeding apparatus and expect to collect anything. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [June 11, 2010, 2:57pm UTC](https://boards.straightdope.com/t/are-there-any-pentapod-creatures/542736/9 "2010-06-11T14:57:05Z")
Because there aren’t enough bands like Dave Brubeck to provide dance music for them? Seriously, animals using a tail as a fifth limb aside, it’s hard to imagine how a land animal with five limbs arranged in radial symmetry would get about in an efficient manner. I can imagine fanciful gaits - picture the thing spinning through the landscape like a whirling dervish. Since wild predators seem to generally lack a sense of humor, it couldn’t escape while they were laughing … ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 11, 2010, 6:13pm UTC](https://boards.straightdope.com/t/are-there-any-pentapod-creatures/542736/10 "2010-06-11T18:13:39Z")
The [Buer](http://www.rahoorkhuit.net/library/ceremonial/classics/plancy/s_p12.gif)? ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [June 11, 2010, 7:43pm UTC](https://boards.straightdope.com/t/are-there-any-pentapod-creatures/542736/11 "2010-06-11T19:43:11Z")
Nearly all Metazoans except the Cnidarians (jellyfish, corals, sea anenomes, and their allies) and the Echinoderms are bilaterally symmetrical, meaning they’ll have an even number of limbs if they have limbs at all. (Even earthworms have setae, bristles used in locomotion, and they’re two to a segment.) Almost all the echinoderms are pentaradially symmetrical, with five or a multiple of five limbs. (The former exceptions, homalozoans, are now tentatively considered basal chordates in some classifications.) In the case of the holothurians and edhinoics (sea cucumbers and sea urchins/sand dollars) the pentaradial symmetry is obscured, in the latter case by an apparent spherical symmetry, but is still present in underlyng structures. In the crinoids and their extinct relatives the blastoids and cystoids, the asteroidea and the ophiuroidea, the five-armed structure is obvious. Of interest is a group of degenerate parasitic forms related to the arthropods, the [Pentastomida](http://en.wikipedia.org/wiki/Pentastomida). Here the mouth and four limbs mimic a pentagonal attach-to-host structure. ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [June 12, 2010, 4:16am UTC](https://boards.straightdope.com/t/are-there-any-pentapod-creatures/542736/12 "2010-06-12T04:16:50Z")
> [@Leo\_Bloom](#): > > a beautiful book by a Brit called Young or Thomas\* on similar themes (even suggesting, in retrospect, some themes of fractal growth. But I can’t remember anything on pentapods. > > \*Cite? [D’Arcy Thompson](http://en.wikipedia.org/wiki/Darcy_Thompson)? New World monkeys, with prehensile tails, could sort of be said to have five limbs.