humans and animals

snail shell

PROPOSAL

SQUID INK SAC

Researchers from the University of Wisconsin-Madison have been studying the Hawaiian bobtail squid. These 3cm long squid have ink sacs on their bellies that don’t just squirt out ink but also glow – a process known as counterillumination. When predators look up at the squid from below, the outline of the squid doesn’t show up as a dark silhouette but instead blends into the bright background of the oceans’ surface. Margaret McFall-Ngai and her team publishing in the journal PNAS have discovered that these ink sacs are capable of not just emitting but also detecting light.

The squid ink sac even has a transparent layer across the surface that acts like a rudimentary lens controlling the direction of the emitted light. By letting more or less light through from the bacteria, squid can match themselves to the brightness of the sea surface that varies depending on how deep down they are and what time of day it is.

looking at animals project2 - SQUID INK SAC

With the exception of nocturnal and very deep water cephalopds, all coeloids which dwell in light conditions have an ink sac, which can be used to expel a cloud of dark ink to confuse predators. This sac is a muscular bag which originated as an extension of the hind gut. It lies beneath the gut and opens into the anus, into which its contents – almost pure melanin – can be squirted; its proximity to the base of the funnel means that the ink can be distributed by ejected water as the cephalopod uses its jet propulsion. The ejected cloud of melanin is bound by mucus particles, so it forms a lump approximately the size and shape of the cephalopod, fixing the predator's attention while the mollusc itself makes a hasty escape.

looking at animals project1

Resources for project 1