BATHYPELAGIC SQUID BATHYTEUTHIS 31 



Description. — The mantle is short and broad; it is widest just 

 posterior to the mantle opening-. The mantle tapers gradually to a 

 bluntly rounded tip, giving it a bullet-shaped outline (pi. 1). In adults 

 the greatest mantle width is about 48% of the mantle length, and the 

 average width is 44%. The margin of the mantle opening has three 

 small, anteriorly projecting triangular lobes that mark the articula- 

 tion points of the two ventral mantle-funnel locking cartilages and the 

 single dorsal mantle-nuchal cartilage. The wall of the mantle is rela- 

 tively thick and muscular, although in individuals that have recently 

 spawned there may be some degradation of the muscle tissue and a 

 thinning of the mantle wall. 



The integumentary layers on the mantle form a thick sheath (pi. 

 2b). The outermost integument consists of small, closely aligned 

 patches that give the skin a velvet-like appearance when observed in 

 natural size. Under magnification, however, the outer integument looks 

 like a very fine-meshed knotless net. Though somewhat variable, the 

 meshes are primarily pentagonal, occasionally hexagonal. The margins 

 of the web-units are very thin and membranous and stand perpendicu- 

 lar to the plane of the mantle wall. These margins of the web are deep- 

 ly colored by maroon-brown pigment. One or two chromatophores of 

 the same color lie in the thin membrane that underlies and intercon- 

 nects the walls of the web. 



A thin sheet containing chromatophores lies immediately beneath 

 the outer reticular layer. The sheet of chromatophores overlies a rela- 

 tively thick, wateiy-gelatinous, transparent, unpigmented layer. This 

 gelatinous layer is supported by a network of ridges that are of greater 

 density than the nearly fluid contents of the pockets made by the in- 

 tersections of the supporting reticulation. These pockets are also pen- 

 tagonal but are larger than those of the outer layer of integument. 



Two additional layers of maroon chromatophores are located be- 

 neath the gelatinous layer. A thick elastic layer of connective tissue 

 and fibers binds the integumentary layers to the muscles of the mantle 

 wall. A few small widely spaced chromatophores lie even in the con- 

 nective tissue very close to the muscular wall of the mantle. 



The fins are small and nearly circular in outline (pi. 1). The bases 

 of the fins are separated posteriorly by the blunt termination of the 

 mantle; they are broadly separated anteriorly by the dorsal surface 

 of the mantle. The bases of the fins are robust and muscular but radial- 

 ly the fin muscle becomes thin and weak, so that the borders of the fins 

 are thin, nearly membranous. The margins of the fins are damaged 

 even in the best -preserved specimens. The rounded anterior fin lobes 

 protrude well forward of the bases of the fins; the rounded posterior 

 lobes extend beyond the end of the mantle. 



