Octopus, Squid & Cuttlefish: A Visual, Scientific Guide to the Oceans' Most Advanced Invertebrates
224
Octopus, Squid & Cuttlefish: A Visual, Scientific Guide to the Oceans' Most Advanced Invertebrates
224eBook
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Overview
Largely shell-less relatives of clams and snails, the marine mollusks in the class Cephalopoda—Greek for “head-foot” —are colorful creatures of many-armed dexterity, often inky self-defense, and highly evolved cognition. They are capable of learning, of retaining information—and of rapid decision-making to avoid predators and find prey. They have eyes and senses rivaling those of vertebrates like birds and fishes, they morph texture and body shape, and they change color faster than a chameleon. In short, they captivate us.
From the long-armed mimic octopus—able to imitate the appearance of swimming flounders and soles—to the aptly named flamboyant cuttlefish, whose undulating waves of color rival the graphic displays of any LCD screen, there are more than seven hundred species of cephalopod. Featuring a selection of species profiles, Octopus, Squid, and Cuttlefish reveals the evolution, anatomy, life history, behaviors, and relationships of these spellbinding animals. Their existence proves that intelligence can develop in very different ways: not only are cephalopods unusually large-brained invertebrates, they also carry two-thirds of their neurons in their arms.
A treasure trove of scientific fact and visual explanation, this worldwide illustrated guide to cephalopods offers a comprehensive review of these fascinating and mysterious underwater invertebrates—from the lone hunting of the octopus, to the social squid, and the prismatic skin signaling of the cuttlefish.
“After reading about the cephalopods’ abilities and behaviors, as well as their potential for advancing our lives, readers might think twice before ordering their next calamari appetizer.” —American Scientist
Product Details
| ISBN-13: | 9780226459738 |
|---|---|
| Publisher: | University of Chicago Press |
| Publication date: | 12/22/2022 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 224 |
| Sales rank: | 97,783 |
| File size: | 36 MB |
| Note: | This product may take a few minutes to download. |
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CHAPTER 1
CEPHALOPOD ANATOMY
ADVANCED INVERTEBRATES
COMPLEX, HIGHLY DEVELOPED NERVOUS AND sensory systems are typical features of living cephalopods. Especially noteworthy are the image-forming eyes and the complex brain, which has evolved from the nerve ring around the esophagus of other molluscs. The ability of most cephalopods to change their appearance rapidly because of specialized pigment organs and reflector cells in the skin that are under direct nervous control makes observation of living animals fascinating. Other noteworthy peculiarities, such as movement by muscles squeezing other muscles, are also characteristic of cephalopods.
EXTERNAL STRUCTURE
Three regions can easily be discerned on a cephalopod. From anterior to posterior, these regions are:
1) the arms and tentacles surrounding the mouth
2) the head, on which the eyes are prominent
3) the sac-like mantle, or body, to which fins may be attached. This overall structure is less distinct in nautilids, which have external shells into which they can withdraw, but is still recognizable.
THE CROWN OF ARMS
Cephalopods other than nautilids have either eight or ten arms surrounding the mouth. On those with ten, two arms are modified into either tentacles (decapods) or filaments (vampires). The arrangement of the arm crown is different in nautilids from that in all other living cephalopods. Nautilids have approximately 90 arms arranged in two rings around the mouth. Each arm is retractable within an outer sheath. The oral surface of each arm is covered by adhesive transverse ridges, rather than by the suckers typical of other cephalopods, which have either eight or ten arms surrounding the mouth. Hence, all living cephalopods other than nautilids have eight arms and some additionally have two tentacles or two filaments.
TENTACLES
The most obvious difference between arms and tentacles on a decapod is in the arrangement of armature (suckers, some of which may be modified into hooks). The arms of most cephalopods have one, two, or four longitudinal series of suckers or hooks extending along the entire oral surface. Tentacles tend to be longer than arms and to have the armature concentrated toward the far end, which is often expanded to form a tentacular club. The filaments of vampires are very long and thin with no armature, and can be retracted into pockets.
Although both decapods and vampires have eight arms and two modified appendages, those modifications are not of the same two appendages. In decapods, the tentacles are ventrolateral, whereas in vampires, the filaments are dorsolateral. Although many people think that the two arms that have been lost in the octopods, out of the general ancestral pattern of ten arms, are the tentacles as found in decapods, it is more likely that it was the dorsolateral arms that are modified in vampires that were lost in octopods.
SUCKERS
Suckers are of exceptional use to cephalopods — the arms and tentacles essentially have the task of delivering the suckers to a destination to conduct feeding, tasting, attachment, or movement. Basic differences exist in the structure of suckers among the major groups. Octopod suckers are radially symmetrical with cylindrical bases that are either broader than the suction cup or only slightly constricted. Decapod suckers are bilaterally symmetrical and their bases are narrow stalks. Therefore, an octopod sucker may be described as looking like a volcano whereas a decapod sucker looks a little like a ball on a stick.
The surface around the inner opening of an octopod sucker has a thin cuticular lining, while the opening of a decapod sucker is characterized by a rigid chitin-like ring that digs into captured prey upon suction and resists the shear forces caused by a wriggling fish or shrimp. These rings may be smooth, notched (referred to as "blunt teeth"), or serrated ("sharp teeth"). The tooth-like structures are of unequal sizes around the opening of the sucker. The result can be elongated sharp teeth in one area of the sucker ring and either blunt teeth or a smooth region on the opposite area. In several squid families, the central elongated tooth in some suckers becomes hyper-developed, forming a hook reminiscent of a cat's claw.
Conical muscular structures, like little fingers, are associated with the bases of the suckers in cirrate octopods, vampires, and most decapods. In cirrates and vampires, both of which have suckers in a single series, these structures are called cirri (singular = cirrus) and are found in pairs alternating with the suckers along part, or all, of the arm. The similar structures on decapods are called trabeculae (singular = trabecula) and extend from the outer bases of the outer series of suckers on the arm or tentacle. Cirri and trabeculae very likely evolved from the same ancestral structure.
In many decapods some suckers in the proximal part of the tentacular clubs develop as simple knobs, alternating with normal suckers. When the two clubs are held together, the knobs on one tentacle align with the matching sucker on the other tentacle and each sucker in that part of the club can attach to a knob. Hence, the tentacular clubs can be attached together at their bases by this overall structure known as a tentacular locking apparatus.
WEBS
In addition to the suckers, the arms have a variety of external structures. Membranes often border the oral surfaces of the arms. Because their function appears to be protection of the suckers, these structures are often described as protective membranes. When these membranes are continuous between adjacent arms, they are called webs. The webs are quite deep in some species, essentially connecting the entire arm to its neighbor. Webs in some species can be very thick and fleshy.
On many decapods, the trabeculae are embedded in the protective membranes, in which case they may be referred to as trabecular membranes. Decapods also have a ridge on the surface of the arms and tentacular clubs away from the suckers. These ridges, known as keels, provide hydrodynamic lift to the head/arm end of the animal when swimming tail-first. The keels on the ventral arms of some squids (such as chiroteuthids and mastigoteuthids) are shifted in position to form a groove in which the thin tentacles are held.
THE MOUTH IN THE MIDDLE
Decapods have a structure around the mouth somewhat similar to an inner ring of arms. A membrane around the mouth, the buccal membrane, is supported by six to eight muscular pillars called lappets. The lappets are like little arms; in some taxa (including some cuttlefishes and inshore squid species, and the family Bathyteuthidae) the lappets have tiny suckers like miniature arm suckers. All functions of the buccal membrane are not known, but in some species sperm packages are implanted on the buccal membrane of the female during mating.
In all cephalopods the mouth is surrounded by a ring of fleshy tissue known as the lips. However, the most prominent feature of the mouth is the hard beak, actually a pair consisting of upper and lower beaks. The upper beak is generally more pointed and the lower is broader, but the edges of both are sharp and come together as an efficient cutting device. When the beaks are closed the upper fits within the lower. The scene in the Walt Disney movie of 20,000 Leagues Under the Sea in which the giant squid attacks the submarine is noteworthy not only for frightening generations of small children, but also because the squid's beak is upside down, looking more like a parrot's beak. The beaks are necessary to cut food into pieces small enough to pass along the esophagus and through the brain. In some species the beaks are also used to create puncture wounds through which to inject poison from the salivary glands into the prey.
Behind the beaks, and between them when the beaks are open, is a tongue-like structure covered with teeth, the radula, a typically molluscan feature. The radula is a ribbon made up of many rows of teeth. It moves forward and backward along a muscular tongue. As each row of teeth crosses the tip of the tongue the teeth become erect to snag pieces of the prey, which are then drawn deeper into the mouth. Below the radula is a salivary papilla used by octopods to dissolve a hole through heavy shells of molluscs and crabs for injection of poison. The beaks, radula, and tongue are embedded within a discrete spherical mass of muscle known as the buccal mass.
EYES THAT SEEM FAMILIAR
The eyes are located laterally on the head. Nautilids have simple eyes in which light refracts through a very small hole, open to the sea, to focus on the retina, much like a pinhole camera. Eyes of almost all other cephalopods are "image forming" and have a transparent spherical lens that more efficiently focuses larger amounts of light on the retina. In oceanic squids, the lenses are exposed to seawater. The groups found in coastal or benthic habitats (inshore squids, cuttlefishes, and incirrate octopods) have a transparent corneal membrane covering the lens, presumably for protection. The details of these corneas differ among groups, indicating evolutionary convergence.
The number of photoreceptors in the retina varies from about 4 million in nautiluses through approximately 20 million in octopuses, to estimates of a billion in the eyes of large squids. Although the eyes of neocoleoids seem to be similar to those of vertebrates, a major difference is the orientation of the photoreceptors in the retina. Whereas retinal nerves in vertebrates are at the end of the cell toward the lens (and therefore the light source), those of cephalopods are at the end of the cell away from the lens. The way the photoreceptors are shaped and packed into the retina allows cephalopods to detect polarization of light, which may be important for communication and coordination with others of their own species and for detection of prey. With the exception of one species, the retinas of cephalopods investigated to date have a single pigment, meaning they are "monochromats" and therefore colorblind. However, research has indicated that the strangely shaped pupils of cuttlefishes (W-shaped) and shallow-water octopods (elongate) may allow them to detect colors based on distortion of the image by the edge of the pupil.
Olfactory papillae are also located on the head, their position varying among groups. Although these organs have been presumed to be sensory based on histology, a physiological response to trace chemicals (odors) in seawater has only recently been demonstrated.
WHERE HEAD MEETS BODY
The junction of the head with the mantle varies substantially among the major groups. In most decapods the head is not fused to the mantle but articulates with it at three points. Where the head and mantle meet dorsally in most decapods, a cartilage-like ridge on the head is matched to a similar groove on the interior of the mantle edge. In some squids this ridge and groove system becomes permanently fused. The dorsal mantle edge is actually attached by muscles and skin to the head in some decapods (some bobtails, for example), vampires, and all octopods. Various crests and folds on the dorsal and lateral areas of the posterior head are characteristic of many decapods.
The funnel lies in the funnel groove, a depression in the posterior ventral surface of the head. The funnel is a tube-like structure through which water is expelled from the mantle cavity along with wastes and, when the animal feels the need, ink. As in so many other particulars, the structure of this feature differs in nautilids from that of other cephalopods and has a different name. The funnel of a nautilid, called a hyponome, consists of two muscular flaps that overlap ventrally but are not fused together. Embryological development of the funnel in neocoleoids begins also as two separate flaps that fuse into a tube before hatching. The funnel is flared at the posterior end, which is located within the mantle cavity. The flaring is continuous with a flap of tissue, the collar, extending laterally and dorsally around the head for the entire mantle opening. The collar allows water to be drawn into the mantle around the mantle opening. It closes like a valve, sealing the mantle opening when the mantle contracts, increasing internal water pressure to accelerate expelled water through the funnel. In some decapods, another flap (the funnel valve) is found on the interior of the narrow outer end of the funnel; it prevents water from entering the funnel "the wrong way" when the mantle is expanding and refilling with water. Also inside the funnel is a secretory apparatus called the funnel organ; this produces mucous to form ink blobs and to expel wastes.
In addition to the nuchal cartilage in decapods, there are two funnel-locking cartilages. These structures lock the free edge of the mantle to the funnel to increase the efficiency of mantle contractions. Some locking apparatuses with complex shapes form a very strong bond whereas others are simple and straight, allowing the components to slide in and out, permitting head retraction into the mantle cavity, while preventing slippage sideways. In some species the locking apparatuses are completely fused.
THE MANTLE OR "BODY"
The muscular molluscan mantle is much more than a sac enclosing the viscera. A complex system of muscles and connective tissue interacts to control the volume of the mantle cavity, the water-filled space inside the mantle. Contraction of transverse muscles causes the mantle wall to become thin and to increase in area. This increase in wall area results in the mantle expanding, drawing water into the mantle cavity through the mantle opening and past the collar. Contraction of the circular muscles decreases the volume of the mantle cavity, resulting in an increase in internal water pressure, sealing the collar and expelling water through the funnel. A third set of muscles, oriented longitudinally, prevents the mantle from elongating too much during mantle contraction. Obliquely arranged fibers of connective tissue, together with inner and outer sheaths of connective tissue (the tunics), store energy when they are stretched by the muscular actions outlined above. This stored energy aids the muscles in the cycle of expansion and contraction.
FINS FOR SOME
A pair of fins attaches laterally to the mantle in all decapods, and in vampires and cirrate octopods. Whereas jetting can result in rapid acceleration, swimming with fins uses energy more efficiently. Having both allows dual-mode swimming. The structure of the fins differs among the groups that have fins and the details of fin attachment vary among decapod families. Different types of fin can be used for flapping and undulation as well as for steering.
ELABORATE AND BEAUTIFUL SKIN
A hallmark of cephalopods is their remarkable skin that produces a vast array of appearances for communication and camouflage. The rapid changeability arises from the brain's direct neural control of millions of pigmented chromatophore organs (each one being either yellow, red, or brown) and iridescent cells (producing all colors) in the skin. Octopuses and cuttlefishes tend to have the most complex skin — equivalent, for example, to a high-resolution digital screen — with a dense concentration of small chromatophores.
Squids generally have fewer chromatophores per mm2 and they are large, hence they are more similar to a low-resolution digital screen. But both are equally fast in their changeability. This skin has an abstract beauty all its own, which will be looked at in more detail in Chapter 4.
INSIDE THE CEPHALOPOD
CEPHALOPODS SEEM VERY DIFFERENT FROM their closest relatives, the gastropods and other molluscs. Their internal organization, however, is constrained by their evolution from a molluscan ancestor. Only upon detailed examination do the anatomical and physiological characteristics become obvious as modifications of the basic molluscan body organization.
SHELLS AND SKULL
Most cephalopods are thought of as being shell-less, but this is not entirely true. As molluscs, the ancestral condition for cephalopods is the presence of an external shell made up of calcium carbonate, as is found in nautilids. In other living cephalopods with a shell, it is internal, reduced, and often not calcareous in composition. These internal structures, which differ in form among major taxonomic groups, are secreted by a shell sac and are the evolutionary equivalent of the shells of other molluscs. Although internal, the shell sac is actually ectoderm that has formed an internal space during embryonic development. The feature of cephalopod shells that is unique among molluscs is a series of gas-filled chambers termed a phragmocone, well known from fossils and in living nautilids.
Cuttlefish shells retain the phragmocone, as do the peculiar ram's horn squids. Most decapods have a pen-like gladius. Vampires have a similar structure, which is one reason that they were once considered to be more closely related to decapods than to octopods, although this now is believed not to be true. Cirrate octopods have a cartilaginous shell that supports their fins, whereas the shells of incirrate octopods are reduced to a couple of rods that support muscle attachment. Some cephalopods have no shell at all.
(Continues…)
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Table of Contents
IntroductionChapter One: Cephalopod Anatomy
Advanced Invertebrates
Inside the Cephalopod Emperor Nautilus
Giant Pacific Octopod
Pharaoh Cuttlefish 46
Bigfin Squid
Japanese Flying Squid
Rough Glass Squid
Chapter Two: Phylogeny & Evolution
500 Million Years of Evolution
Nautilus—Living Fossil?
Evolution of Coleoids
The Buoyancy Conundrum
Octopodiformes
Decapodiformes
Cephalopods & Fishes: Convergent Evolution
On Dwarfs & Giants
Evolution & Climate Change Fuzzy Nautilus
Common Blanket Octopus
Vampire
Two-toned Pygmy Idiosepiid
Caribbean Reef Octopus
Flamboyant Cuttlefish
Analogous Bobtail Squid
Opalescent Inshore Squid
Eye-flash Squid
Chapter Three: Peculiar Lifestyles
Reproduction
Development
Age & Growth
Locomotion
Cephalopods of Various Biomes
Migration Humboldt Squid
Greater Argonaut
Striped Pyjama Squid
Thumbstall Squid
Agassiz’s Whiplash Squid
Pacific Warty Octopod
Balloon Dumbo Octopod
Chapter Four: Behavior, Cognition & Intelligence
Decision Making
Rapid Adaptive Coloration
Nature’s Best Camouflage
When Camouflage Fails
Super Fights for Mates
Sneaky Males & Sneakier Females
Evaluating Intelligence in Such Bizarre Animals Common Octopus
Day Octopus
Mimic Octopus
Common European Cuttlefish
Giant Australian Cuttlefish
Broadclub Cuttlefish
Long-finned Inshore Squid
Caribbean Reef Squid
Chapter Five: Cephalopods & Humans
World Fisheries & Human Consumption
A Rich History of Biomedical & Biological Advances
Bio-inspired Materials Science & Engineering Horned Octopod
Lesser Two-spotted Octopod
Southern Blue-ringed Octopus
Hawaiian Bobtail
Cape Hope Squid
Veined Squid
Jewel Squid
Sparkling Enope Squid
Glossary
Resources
Notes on Contributors
Index
Acknowledgments