Octopus (28 page)

Although the war between giant squid and their sperm whale predators has been depicted as a battle, this appears not to be the case. There is no evidence beyond the sucker scars that sperm whales ever have much trouble eating a giant squid. Mariners have seen sperm whales bringing giant squid to the surface to eat them. Such reports typically recount that the whales were methodically munching their way through the squid with their muscular toothed lower jaw and swallowing them with ease.

It's quite a jump from the fast, sleek, open-ocean true squid to the bottom-living and much slower sepiolid squid, which resemble cuttlefish. On the surface, they look much like octopuses, but there are big differences. Many sepiolids are nocturnal and so small, 2 in. (5 cm), they are easy to overlook, even though they are very common.

The stubby squid is not a true squid but a sepiolid, but it's otherwise appropriately named since it is very short. The sepiolid squid are one of a group that lives mostly on or near the bottom. They are mostly small, less than 4 in. (10 cm) in mantle length, and live less than six months. They look like a cross between an octopus and a cuttlefish, with large round eyes, a fin on each side of the body, and two long prey-catching tentacles like squid. Stubby squid range around the rim of the North Pacific in water down to 3000 ft. (1000 m) deep. They feed mostly on shrimp, which they catch with their two long tentacles. They have a small beak that they use to chew
shrimp like we eat corn on the cob, eating them from the center toward each end, consuming most of the tail meat and the internal organs from the body of the shrimp and leaving the shell. They are alert at night, when divers see them sitting on the sand or mud bottom watching for shrimp, predators, or mates.

To avoid getting seen during the day by visual predators, the stubby squid buries itself in the substrate, using a fixed action pattern—a set of the same behaviors used in the same sequence each time—for burying. It sits on the sand and blows underneath, first forward with its water jet then backward, and continues blowing forward then backward alternately until it creates a depression in the sand where it sits. Then it reaches out on both sides at a 45-degree angle with its second pair of arms, scooping up a bit of sand, pulling it close, and then throwing it on its body and head. It repeats this throwing action until it is covered with sand.

Once covered, the squid consolidates the sand next to its body with thick mucus from the skin and pokes its eyes up through the sand. It aims its funnel straight upward and blows one or two strong water jets out to clear a breathing hole. Then, keeping the funnel pointed upward, it breathes more shallowly than the octopus, taking water in through the gill slits and out the funnel. It sits in this mucus-bound cocoon through the day, protected from predators by being almost totally out of sight.

One of the largest of the cuttlefish group, and well known because it has been hunted by humans for food for centuries, is the common cuttlefish of European waters. Full size at 1 ft. (
m) in length after a lifespan of one and a half years and living near shore over sandy mud bottoms, the cuttlefish is a valued food item. Like the octopus, it lives near the sea bottom but one clear difference between the octopus and cuttlefish is buoyancy. Cuttlefish have a wide calcareous cuttlebone just inside the dorsal surface of the mantle. Its many chambers all have air inside them, which helps the fairly heavy-bodied animal to keep buoyant. The cuttlebone is given to caged birds for them to nibble at and take in calcium. The cuttlefish is a bottom dweller like the octopus, although it does not need to be, and even sometimes buries itself in the sand. In the daytime, like stubby squid, it is almost invisible under a sand layer.

Even though they can float all the time, cuttlefish are like octopuses in that they spend much of their time hiding in the landscape. But cuttlefish also have a truly great repertoire of colors and patterns on the skin. Cuttlefish skin patterns have the same eyespot pattern that squid have, they have dapples and dots, and they make zebra stripes as an antagonistic signal. It's even rumored that if you put a small cuttlefish onto a black-and-white checkerboard pattern, it will make the same checkerboard on its skin. Keri Langridge et al. (2007) are beginning to separate out the various postures and patterns that cuttlefish make to a potential predator (also see Hanlon and Messenger 1988). Having this repertoire of skin patterns and colors may sound like a paradox, since the cuttlefish is usually buried under sand all day and is only active at night when there isn't much light for anything to see these patterns. Maybe, like the octopus, it comes out sometimes in the day. Or maybe there was huge selection pressure to get the appearances right even though they weren't used very often. Or maybe cuttlefish can't always find sand.

When they are out of the sand, cuttlefish are generalist predators like octopuses, but the prey species they take and the way they catch them are different. Like true squid, cuttlefish have a pair of elastic, extensible tentacles. These can be shot out, just like chameleons flip out their tongue, to grab small prey, often assisted by suckers on the tentacle tips that make sure the prey stays caught. And cuttlefish are flexible in capture technique: if a prey animal such as a crab is slow and too big to catch with the tentacles, they will just grab it with the arms. They may also blow sand off buried crabs and use their tentacle tips as a lure. And cuttlefish have a distinctive feature: they nearly always use vision to help them find prey, and there's no exploring in the rocks and crevices like the octopus. Not much of the cuttlefish brain is allocated to processing touch information.

Compared with the common octopus, there has been almost no field observation of behavior of the common cuttlefish. We don't know why, since the cuttlefish is a very common species in European waters and a valuable food resource. Cuttlefish live near shore, and though they often are found in muddy water, they are certainly big enough at around 1 ft. (
m) mantle length to watch easily. They have been raised in captivity, and a lot of work has been done in the lab on their early behavior, as well as on their reproductive interactions, much by Boal (2006).

Cuttlefish probably have much more interesting sex lives at the end of their one-year life spans than octopuses, based on lab work and field observations of the giant cuttlefish in Australia. Even when they are mature, most octopuses don't seem to encounter each other a lot, but cuttlefish often migrate to spawning areas where males compete for access to females. Males give each other zebra stripe skin displays and even engage in
physical battles. In the restricted environment of the lab, they corner females, mate with them head-to-head, and even try to blow the sperm of previous males out of the females' oviducal gland with a jet of water. Females sit back and decide which male to accept. They may use chemical cues to guide their choice. Boal set up choice tests in 1997, and found that females chose those males that had successfully mated with other females, not just the biggest males. Unlike in the octopus, there is no care of eggs in cuttlefish. The eggs are attached to rocks or algae by females, and then both sexes die.

On a small rocky reef in South Australia in 2002, Katrina Hall and Roger Hanlon observed a huge aggregation of giant cuttlefish (Sepia apama) ready to reproduce. Such mating aggregations can be spectacular, like a cuttlefish singles bar. Females stay for a short time, and so they may have just arrived, because there were four males around for each female. Big males guarded or tried to guard a female, though without long-term success, because pairings only lasted ten to fifteen minutes. Bigger ones always won contests. Smaller males waited around until a guarding male was distracted and then tried a quick courtship of females. They would take on the skin patterns typical for a female and hang around her without the guarding male noticing. They probably didn't fool her, though, as over 70 percent of all mating attempts by males were rejected and females had a specific skin display to indicate they weren't interested. With over 41,000 giant cuttlefish in the area and a density of about one per square yard, it must have been a sight to see. The common cuttlefish probably does something like this though in smaller groups.

Hardly anyone knows much about the vampire squid, but two things stand out: it's very different from other coleoid cephalopods, and it's well adapted to the harsh environment of the ocean depths. Taxonomists worry about where to put Vampyroteuthis, referred to as the vampire squid (even though it's not a squid) because that's what the name means. Some taxonomists place it in a separate order, the Vampyromorpha, within the Octopods, and some put it in a separate group completely.

The systematists put the vampire squid halfway between the squid and the octopuses on the family tree. Two things stand out about the vampire squid: it's very different from its octopod and squid relatives, and it's well adapted to the depths of the oceans in which it lives. Vampire squid differ from other coleoids in several ways. They have peglike cirri instead of suckers on their arms like some of the deep-sea octopuses, and they also
have fins like the squid do, though the fins are elongate and attached to the posterior instead of attached laterally like in the squid. Vampire squid have no chromatophores except near the photophores, or light organs, so they are poor at color changes. They have lost the ink sac and the specialized hectocotylized arm. Most unusually, they have a pair of long filaments that are like tentacles but much more fragile, usually kept tucked in pits between the first two arm pairs. They trail these long filaments through the water as they move, trolling for prey in the same way we might troll for salmon. When a prey species hits a filament, the squid will circle back to pick it up with the arms. These structures aren't a standard set for coleoid cephalopods, but the lack of chromatophores and the presence of filaments and cirri make sense when we realize that vampire squid drift in the dark, deep sea, between 1800 and 3000 ft. (600 and 900 m) down. Because vampire squid live at such depths, many of our ideas about how they live are guesses. Until ROVs started taking videos deep in the ocean, scientists were basically working on preserved bodies of animals that had been trawled up from the depths.