 Bigfin reef squids are characterised by a large oval fin that extends throughout the margins of its mantle , giving them a superficial similarity to cuttlefish . They are small to medium @-@ sized squids , averaging 3 @.@ 8 to 33 centimetres ( 1 @.@ 5 to 13 @.@ 0 in ) in length . They exhibit elaborate mating displays and usually spawn in May , but it can vary by location . The paralarvae resemble miniature adults and are remarkable for already having the capability to change body colouration upon hatching . Bigfin reef squids have the fastest recorded growth rates of any large marine invertebrate , reaching 600 g ( 1 @.@ 3 lb ) in only four months . They are a short @-@ lived species , with a maximum recorded lifespan of 315 days . 
