Feeding mechanisms and diet in cephalopods : special reference to Antarctic mesopelagic squid
The diet of 12 species of Antarctic squid was investigated using conventional and serological methods. Antisera were raised to the Antarctic krill, Euphausia superba . A scoring system of 0-20 was devised for Laurell Fused Rocket gels, with a threshold of significance of &'62 &'61 7. Fixed material cannot be identified by serology, but samples partially denatured by repeated freeze-thawing are still viable. Despite denaturing of protein as digestion progresses, antiserum can detect E. superba in the stomach, caecum, digestive gland and intestine. Antisera specificity was investigated by testing for cross-reactions with 13 species of Antarctic crustaceans and screening non-antarctic squid. The antisera were not specific to E. superba but could be used to screen for Euphausia sp. The diet of Martialia hyadesi was predominantly fish. Alluroteuthis antarcticus , Galiteuthis glacialis , Gonatus antarcticus and Psychroteuthis glacialis also eat fish. P. glacialis eats E. superba . Mastigoteuthis psychrophila , Moroteuthis knipovitchi and Moroteuthis robsoni eat Euphausia sp. P. glacialis and M. hyadesi both eat cephalopods. This is cannibalism in the latter species. The functional morphology and biomechanics of the cephalopod buccal mass was investigated by dissection, histology and electrophysiology experiments. The buccal mass shows negative allometric growth, and weighs proportionally less in octopods than decapods. The superior mandibular muscle is responsible for closing the beaks. The inferior mandibular muscle retracts the beaks during closing, causing shearing. The lateral mandibular muscle opens the beaks and flexes the upper beak lateral wall. There are species differences in muscle layout. Beak shape influences muscle volume. Beccublast cells were found associated with the biting musculature. The cycle of movements during biting is: opening, closing, retraction, and then protraction and reopening to return to the starting point. There is no joint in cephalopod beaks. The jaws slide and rotate round an area rather than a point. Cephalopod beaks divide into four types on the basis of mechanical advantage and muscle mass (F1). There are: (1) 'strong' with a large F1, (2) 'strong' with a small F1, (3) 'fast' with a large F1, and (4) 'fast' with a small F1. There are no significant differences between the maximum load (g) versus body weight (g) relationships for Loligo and Eledone , despite variations in muscle mass and mechanical advantage. Maximum curves suggest that the load-weight relationship flattens out with growth.