Connecting stripes: An organic skeletal structure in Sepia from Red Sea

Abstract

The skeletal structure, herein termed “connecting stripes”, is demonstrated in dried cuttlebones of Sepia (Acanthosepion) savignyi de Blainville from the Gulf of Aqaba, Red Sea, Eilat, Israel. This structure consists of segmented chitinous strip-like sheets covering the outside opening to the cuttlebone chambers. Scanning electron microscope images demonstrate that the connecting stripes are tightly attached to the neighbouring septa along the septal edges and do not continue from one chamber to the next. When broken, they leave band-like remnants along the attachment sites. The connecting stripes consist of fibrous, organic, possibly mainly chitinous, laminas. Chemical analysis using energy dispersive spectrometry shows that the connecting stripes contain C, O, Na, K but lack Ca and P. The connecting stripes show perceptible, usually barely visible micropores with diameter of ca. 0.1μm; distances between the micropores are 0.2 to 0.3μm. The connecting stripes in Sepia are similar to connecting rings in bactritoids and ammonoids in having a segmented structure and a non-mineralized, organic composition. The microporosity of connecting stripes observed in Sepia has been also recorded in three genera of Mesozoic ammonoids. The connecting stripes may serve as a transport route of the cameral liquid in and out of the chambers and are considered to be a homologue of the connecting rings in cephalopods with a fully developed siphonal tube.