# Are there any monocular animals? There must be... **URL:** \ **Category:** Factual Questions\ **Created:** [November 4, 2013, 2:52pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058 "2013-11-04T14:52:09Z")\ **Posts on this page:** 20\ **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:** [November 4, 2013, 2:52pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/1 "2013-11-04T14:52:09Z")
I had a dream. A nightmare, actually, which starred me being chased by a Spielberg velociraptor animal except for instead of a neck and reptilian head it had, in correct sizing of that combined length and neck width, a bellows-like short elephant-trunk-y appendage ending with an eyeball peering out, half embedded like in our eye socket. So. See subject. ---
**Author:** ![Tom\_Tildrum](https://avatars.discourse-cdn.com/v4/letter/t/e95f7d/32.png) [@Tom\_Tildrum](https://boards.straightdope.com/u/Tom_Tildrum)\ **Post date:** [November 4, 2013, 2:56pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/2 "2013-11-04T14:56:21Z")
Many birds have eyes almost on opposite sides of their heads, such that the stereoscopic portion of their field of view is extremely narrow. ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [November 4, 2013, 3:05pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/3 "2013-11-04T15:05:44Z")
Bilateral symmetry is so common in animals, down to the smallest, that I can’t think where a single-eye physical form would come from. ---
**Author:** ![BubbaDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bubbadog/32/333_2.png) [@BubbaDog](https://boards.straightdope.com/u/BubbaDog)\ **Post date:** [November 4, 2013, 3:15pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/4 "2013-11-04T15:15:55Z")
Low on the bio-complexity level but howsabout the [euglen](http://blogs.unimelb.edu.au/sciencecommunication/2013/08/12/12978/)a? ---
**Author:** ![RealityChuck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/realitychuck/32/195_2.png) [@RealityChuck](https://boards.straightdope.com/u/RealityChuck)\ **Post date:** [November 4, 2013, 3:17pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/5 "2013-11-04T15:17:54Z")
The starfish has a single eyespot. ---
**Author:** ![Prof.Pepperwinkle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/prof.pepperwinkle/32/13627_2.png) [@Prof.Pepperwinkle](https://boards.straightdope.com/u/Prof.Pepperwinkle)\ **Post date:** [November 4, 2013, 3:19pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/6 "2013-11-04T15:19:56Z")
There’s a type of tiny crustacean called the [Cyclops](http://en.wikipedia.org/wiki/Cyclops_(genus)) or water flea. ---
**Author:** ![DocCathode](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/doccathode/32/18773_2.png) [@DocCathode](https://boards.straightdope.com/u/DocCathode)\ **Post date:** [November 4, 2013, 4:27pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/7 "2013-11-04T16:27:36Z")
There is a species of jellyfish with a single eye. The eye is badly farsighted. I can’t remember the name of the species. I learned about it here on the Dope. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [November 4, 2013, 4:39pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/8 "2013-11-04T16:39:19Z")
> [@RealityChuck](#): > > The starfish has a single eyespot. Starfish actually have an [eye at the end of each arm](http://news.discovery.com/animals/starfish-see-the-world-using-eyes-on-the-tips-of-their-arms-130706.htm), so most species have five of them. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [November 4, 2013, 5:45pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/9 "2013-11-04T17:45:29Z")
There are spiders with an uneven number of eyes. One of those must fit your criterion. ---
**Author:** ![Uniqueorn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/uniqueorn/32/2807_2.png) [@Uniqueorn](https://boards.straightdope.com/u/Uniqueorn)\ **Post date:** [November 4, 2013, 6:00pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/10 "2013-11-04T18:00:43Z")
What would the evolutionary advantage be? ---
**Author:** ![DocCathode](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/doccathode/32/18773_2.png) [@DocCathode](https://boards.straightdope.com/u/DocCathode)\ **Post date:** [November 4, 2013, 6:04pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/11 "2013-11-04T18:04:44Z")
> [@CC](#): > > There are spiders with an uneven number of eyes. One of those must fit your criterion. I don’t think so. Every close up of a spider I’ve ever seen shows at least two eyes. Re Jellyfish Some quick Googling has turned up that all jellyfish eyes are farsighted. I can’t find a page with a pic of the one eyed jellyfish yet. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [November 4, 2013, 6:06pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/12 "2013-11-04T18:06:14Z")
> [@CC](#): > > There are spiders with an uneven number of eyes. One of those must fit your criterion. I’m wrong. But there is the tuatara (q.v.) that has some sort of third eye that scientists haven’t quite figured out. ---
**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:** [November 4, 2013, 6:30pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/13 "2013-11-04T18:30:00Z")
> [@CC](#): > > I’m wrong. But there is the tuatara (q.v.) that has some sort of third eye that scientists haven’t quite figured out. More to the point, _Triops_ is a shrimp with a third eye in the back, which appears to be capable of sight. From behind, Triops is effectively a one-eyed creature > **[Triops longicaudatus](https://en.wikipedia.org/wiki/Triops_longicaudatus)** > > Apus longicaudatus LeConte, 1846 > Triops longicaudatus (commonly called American tadpole shrimp or longtail tadpole shrimp) is a freshwater crustacean of the order Notostraca, resembling a miniature horseshoe crab. It is characterized by an elongated, segmented body, a flattened shield-like brownish carapace covering two thirds of the thorax, and two long filaments on the abdomen. The genus name Triops comes from Greek ὤψ or ṓps, meaning "eye" prefixed with Latin tri-, "three", in reference to... The tuatara probably can’t see out of that rear eye, which seems to be associated with daily rhythm. The human pineal gland is similarly light-sensitive, despite being inside the brain and away from light. ---
**Author:** ![Blue\_Blistering\_Barnacle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blue_blistering_barnacle/32/3386_2.png) [@Blue\_Blistering\_Barnacle](https://boards.straightdope.com/u/Blue_Blistering_Barnacle)\ **Post date:** [November 4, 2013, 6:30pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/14 "2013-11-04T18:30:42Z")
Opabinia had 5 eyes on short stalks, one of which was unpaired. It also has a trunk (proboscis) with a grabby mouth-like thing at the end. > **[Opabinia](https://en.wikipedia.org/wiki/Opabinia)** > > Opabinia regalis is an extinct, stem group arthropod found in the Middle Cambrian Burgess Shale Lagerstätte (505 million years ago) of British Columbia. Opabinia was a soft-bodied animal, measuring up to 7 cm in body length, and its segmented trunk had flaps along the sides and a fan-shaped tail. The head shows unusual features: five eyes, a mouth under the head and facing backwards, and a clawed proboscis that probably passed food to the mouth. Opabinia probably lived on the seafloor, using t... I’ll bet it somehow invaded your dreamscape and somehow mated with a velociraptor. ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [November 4, 2013, 6:33pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/15 "2013-11-04T18:33:31Z")
> [@Uniqueorn](#): > > What would the evolutionary advantage be? Probably none. That’s why if there are any, they’re rare. But perhaps their one eye is somehow linked to a characteristic that is an evolutionary advantage. ---
**Author:** ![Peaton\_of\_peat](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@Peaton\_of\_peat](https://boards.straightdope.com/u/Peaton_of_peat)\ **Post date:** [November 4, 2013, 6:37pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/16 "2013-11-04T18:37:25Z")
Lots of insects have a cluster of three ocelli on their foreheads. [Hymenoptera](http://farm9.staticflickr.com/8301/7750313218_ec26542710_z.jpg) (bees, wasps, and ants) and [cicadas](http://farm9.staticflickr.com/8165/7657215820_64223a5c7e_z.jpg) spring to mind, but [mantids](http://spleen-me.com/blog/wp-content/uploads/2008/12/dsc_1183.jpg) have them too. Looking for pictures tells me that plenty of others have them too but you never see them because they don’t let you get close, like [mayflies](http://farm9.static.flickr.com/8143/7280327688_ccb9881ce7_m.jpg) and [dragonflies](http://farm2.staticflickr.com/1440/1090483796_cf3cc54386_z.jpg?zz=1) (squashed in between the compound eyes) and [damselflies](http://www.naturenorth.com/dragonfly/DOM/Images/08_ocelli.jpg) and even [flies](http://archives.evergreen.edu/webpages/curricular/2011-2012/m2o1112/web/images/ocellar-triangle.jpg). That last one surprised me because I figured the more “advanced” insects had all lost them, since beetles and butterflies don’t seem to have them. Those are all multiple eyes though, even if they are odd-numbered. Like **Prof. Pepperwinkle** , only living thing with no more than one eye that comes to mind off-hand is _Cyclops_. If extinct critters count, back in the day there were monocular trilobites, I think I saw a fossil of one at the Smithsonian but it’s hard to find good pictures of them online. ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [November 4, 2013, 7:33pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/17 "2013-11-04T19:33:05Z")
> [@DocCathode](#): > > Re Jellyfish > > Some quick Googling has turned up that all jellyfish eyes are farsighted. I can’t find a page with a pic of the one eyed jellyfish yet. Cite? According to [this Wikipedia article](https://en.wikipedia.org/wiki/Box_jellyfish), the box jellyfish is the only type of jellyfish that has eyes that focus light at all. Others only have simple eye spots or pits, that do not form images, so the concepts of near or far sighted is not applicable to them. Furthermore, I have difficulty believing that box jellyfish have gone to all the trouble of inventing eyes that can focus light, only to leave them all with sub-optimal focus. They may (very likely) not be able to change the focus of their eyes, like humans can, and it may be that the focus is fixed optimally for distance rather than close up, detail, vision, but that is hardly the same thing as “farsighted” as that term is applied to humans. ---
**Author:** ![Tim\_R.Mortiss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tim_r.mortiss/32/142_2.png) [@Tim\_R.Mortiss](https://boards.straightdope.com/u/Tim_R.Mortiss)\ **Post date:** [November 4, 2013, 7:55pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/18 "2013-11-04T19:55:41Z")
Quick googling at work failed to turn up a picture of the famous “One-Eyed Penisaurus” from _Flesh Gordon_. Nor did I want to look too hard while at the office! ---
**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:** [November 4, 2013, 8:12pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/19 "2013-11-04T20:12:25Z")
> [@Colibri](#): > > Starfish actually have an [eye at the end of each arm](http://news.discovery.com/animals/starfish-see-the-world-using-eyes-on-the-tips-of-their-arms-130706.htm), so most species have five of them. Get ahold of Retief, the Groaci are invading. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [November 4, 2013, 8:22pm UTC](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058/20 "2013-11-04T20:22:47Z")
> [@CC](#): > > I’m wrong. But there is the tuatara (q.v.) that has some sort of third eye that scientists haven’t quite figured out. Many vertebrates from fish to reptiles have some version of this third or [parietal eye.](http://en.wikipedia.org/wiki/Parietal_eye) The tuatara has the best developed version among living forms. However, many extinct species may have had more functional third eyes in between the two lateral eyes. [Next page](https://boards.straightdope.com/t/are-there-any-monocular-animals-there-must-be/673058.md?page=2)