What aquatic animals hunt in packs?

I have a little problem with the term pack (English is not my first language) because I don't know wether it could be extensive to shoars and schools of fishes. In the case it is, then schools of herrings hunting copepods could match your question (see wikipedia Forage fish, for more information). Please if anybody can clarify this, it would be very helpful, at least for my English.

But in any case, non-mammals hunting cooperatively are very interesting, because this behaviour is less known than that of dolphins and orcas.
There is this nice article Reef alliances: goatfish hunt in packs, while groupers team up with moray eels - Not Exactly Rocket Science giving some interesting examples:

• Goatfish's packs can hunt in a similar way to lion packs. Goatfish live in the Red Sea, and usually forage alone. They only team up when they hunt among corals. The moment one fish  shoots off towards a target, the others join in the hunt. Once the  chaser drives its prey into coral crevices, the others act as blockers,  swimming around to cut it off.

A colourful goatfish.

• groupers and giant moray eels provide compelling evidence for interspecific cooperative hunting. They also live in the Red Sea.

Groupers will visit moray eels at their resting places and provide  visual signals (such as a head shake) to engage morays in the hunt.  These associations are non-random and appear to be motivated by the  hunger level of the groupers. Groupers were able to capture prey five  times more quickly with morays present because the eels could sneak  through crevices and corner prey items; additionally, morays that hunted  alone were never successful because they did not have a grouper present  to lead them to the prey. Thus, the hunting success of groupers and  giant moray eels is greater for both species than when hunting alone.

I find interesting to remark that those two types of pack hunting have been studied by the same investigator, Reduan Bsary (http://www2.unine.ch/ethol/page-...).

I went on looking for more examples, because I thought that vertebrates don't have the exclusive of all kind of complex behaviors. I found that

• Humboldt squids hunt schools of fish, showing extraordinary cooperation and  communication in its hunting techniques. This is the first observation  of such behaviour in invertebrates (http://www.outsideonline.com/192...).

But I think that there is many more to be discovered. Some lobster practise pack migration, so could crustaceans give some more surprises?, I don't know.

I'm amazed by the way in which some animals combine very strongly hard-driven fixed behavior with some amazing moments of more complex one.