110 Sharks: The Animal Answer GuideMost internal parasites are small, wormlike animals. But others are
large and have backbones. For example, when researchers cut open a 395-
kg (870-lb) Shortfin Mako Shark caught off New York, they found two live
Snubnose Parasitic Eels (Simenchelys parasiticus) curled up happily inside
the shark’s heart. The eels, which are true bony fishes, were about 20 cm
(8 in) long, took up most of the space in the heart, and had shark blood in
their guts. It was difficult to say how long they had lived there, but scar tis-
sue in the heart indicated that the eels had been there quite a while.
Most of the external parasites on sharks can move across the skin and
around the scales. They may find the hard dermal denticles and thick skin
of sharks a challenge for attachment. But others seek smoother, softer body
parts where they can anchor themselves. One example is a particular type
of copepod, Ommatokoita elongata, which targets the eyeballs of Greenland
Sharks. Ommatokoita is a good example of a habitat-specific parasite; it is a
5-cm (2-in) copepod that penetrates the shark’s eyeballs and feeds on the
surface of the cornea. The parasite isn’t fatal; sharks with parasites embed-
ded in both eyes are functionally blind but still grow to large sizes and feed
successfully.
Reflecting on all this information about internal and external parasites
can change how we look at sharks. When you see a shark swim by in the
wild or at a public aquarium, try to realize that what you are seeing is not
just a single animal but more like an entire, highly evolved, mobile ecosys-
tem.Eyeball from a Greenland Shark in-
fected with a parasitic Ommatokoita
elongata copepod. The photo shows
a female Ommatokoita anchored
in the shark’s eyeball via a pair of
modified legs. Her egg cases are the
white bulb-like structures protrud-
ing from the eyeball to the right. An
infected shark may be essentially
blinded by the copepod but is still
able to feed successfully. Photo courtesy
of George Benz
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