Morphology and function of the mandibular muscles in some coleoid cephalopods

Abstract

The functional morphology of the buccal mass of 23 species of cephalopod (Octopoda, 4 species; Teuthoidea, 17; Sepioidea, 2) was investigated by gross dissection, histology and observations on fresh preparations. Cephalopod beaks lack a joint or articulation point. The jaws slide and rotate around an area rather than a fixed point. During closing the superior mandibular muscle (SMM) provides the force of a bite and the largest movement vector, whilst the inferior mandibular muscle (IMM) acts to retract the upper beak, causing shearing action. Dorsal portions of the lateral mandibular muscles (LMM) flex the upper beak walls outwards, probably to accommodate the backwards sweep of the radula and buccal palps during closing. To open the beaks, the ventral portions of the lateral mandibular muscles pull the rear lateral walls of the two beaks towards each other, moving the lower beak back relative to the upper.

A deep‐sea octopus (Graneledone cf. boreopacifica) as a shell‐crushing hydrothermal vent predator

“…(Kear, 1994). The angle correlates with the volume, and therefore the force, of the superior mandibular muscle, the prime mover in beak closure (Kear, 1994). The large beaks, the voluminous beakclosing muscle and the deep scratches seen on the beaks of species of Graneledone support the hypothesis that these beaks crush gastropod shells.…”

“…Cephalopod beaks in vitro can exert considerable force (e.g. up to a 560 g load from the beak of a 380 g Sepia) (Kear, 1994). The angle between the wings and lateral walls of the lower beaks of Graneledone spp.…”

“…is larger than in those of Eledone spp. (Kear, 1994). The angle correlates with the volume, and therefore the force, of the superior mandibular muscle, the prime mover in beak closure (Kear, 1994).…”

Ontogeny of the digestive system of the Octopus bimaculatus paralarvae (Verril, 1883)

“…The buccal mass is fortified with two mandibles, which, according to Lowenstam et al ([ 1984 ]), are constituted of chitin hardened by means of mineral deposits like calcite and magnesite. In addition they are surrounded with muscular fibers for support and movement facilitation (Heinrich [ 1904 ]; Kear [ 1994 ]; Boucaud-Camou and Roper [ 1998 ]). The radula is exclusive of the mollusks, except bivalves and scaphopodes, and its structure is used for systematic classification (Aldrich et al [ 1971 ]).…”

Two Coleoid Jaws From the Upper Cretaceous of Hokkaido, Japan

“…Each jaw is made up of outer and inner lamellae, which are joined anteriorly. In Recent cephalopods, upper and lower jaws and a radula are accommodated in the proximal portion of the digestive system (buccal mass) and their function is to bite and shear food by means of the strong jaw-radular muscular system (Kear, 1994;Tanabe and Fukuda, 1999). Cephalopod jaws are composed mainly of a hard chitinous material (Saunders et al, 1978;Hunt and Nixon, 1981), so that they have a preservation potential as fossils when they have been diagenetically replaced by phosphatic material (Tanabe and Fukuda, 1983;Tanabe et al, 2001).…”