Ommatokoita: (No) sight for sore eyes

pacific-sleeper-shark
Pacific Sleeper Shark (Somniosus pacificus)

I spy with my little eye something beginning with O…..

However if you’re either the Pacific sleeper shark (Somniosus pacificus) or Greenland shark (Somniosus microcephalus)it is likely that you will see nothing all thanks to an ectoparasite on your eye: Ommatokoita. Currently there are only two known species: Ommatokoita elongata and Ommatokoita superba and they are found exclusively on the eyes of these sharks, which are both large, deep-water dwelling species.

In 1998, Boruscinska, Venz and Whiteley captured and collected the eyes from six Greenland sharks and harvested their eyes (whether this benefited the sharks in anyway was not recorded) and without exception, all sharks were infected.

greenland-shakr
Removed eye taken from an infected Greenland shark with female O. elongata

All the species observed where O. elongata transformed adult females. These  were attached to the cornea by means of an anchoring structure; the bulla,(which is unique to copepods).

Excuse me whilst I check my eyes forever.

Despite the size of these parasites (5cm-6cm in total, including both female and trailing embryo sac), they don’t affect the health of the shark, with five out of the six sharks being a healthy colour and a picture of health (excluding the parasite bouncing on it’s face), sadly the sixth shark was eaten whilst on the line by other sharks (the paper didn’t say which species).

 

copepod
Greenland shark with O. elongata attached to the cornea. These species are a Goliath of the family with most copepods being 1-2mm long. And I thought dusts in my eyes was bad

So far there is no data to show a clear life-cycle but adult male O. elogatas were found fixed superficially to the host shark, and are considerably smaller than the females. Females are also able to detach themselves from the bulla and swim freely when not feeding of shark and are a pinkish-white colour.

The reasons for the female choosing such a bizarre place to anchor, maybe that shark skin is covered in miniature, flat V-shaped scales celled denticles, more akin to teeth than scales, making them difficult to attach to.  It would also be considerably more difficult for the shark to dislodge this unwelcome visitor from the eye as it cannot scratch them against at an abrasive surface (e.g. ocean floor or a rock) like it would the skin, without causing irreparable damage as these shark eyes heal slowly.

*Fun fact: In August 2016 a female Greenland shark was found to be approximately 329 years old, making them a strong contender for longest living vertebrate, this study also  showed that females don’t breed until 150 years old.  However this has yet to be proven beyond a reasonable doubt.

References:

BBC. (2017). Shark – Greenland shark – BBC One. [online] Available at: http://www.bbc.co.uk/programmes/articles/4XR3dG1nHXGXtyj1Rt262sv/greenland-shark.

Borucinska, J., Benz, G. and Whiteley, H. (1998). Ocular lesions associated with attachment of the parasitic copepod Ommatokoita elongata (Grant) to corneas of Greenland sharks, Somniosus microcephalus (Bloch & Schneider). Journal of Fish Diseases, 21(6), pp.415-422.

Marinespecies.org. (2017). The World of Copepods – Intro. [online] Available at: http://www.marinespecies.org/copepoda/.

Marinespecies.org. (2017). WoRMS – World Register of Marine Species – Ommatokoita Leigh-Sharpe, 1926. [online] Available at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=135608&allchildren=1.

Ocean Portal | Smithsonian. (2017). Biomimicry Shark Denticles. [online] Available at: https://ocean.si.edu/ocean-photos/biomimicry-shark-denticles.

Davis, N. (2017). 400-year-old Greenland shark is oldest vertebrate animal. [online] the Guardian. Available at: https://www.theguardian.com/environment/2016/aug/11/400-year-old-greenland-shark-is-the-oldest-vertebrate-animal.

 

 

 

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