Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Octopoteuthidae is a family of squid comprising two genera. The family is characterised by tentacles which cease to grow after the paralarval stage; and the use of a penis, instead of a hectocotylus. Squid are marine cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two longer tentacles. (The only known exception is the bigfin squid group, which have ten very long, thin arms of equal length.)