About 7650 species one thousand Mostly species live in marine fresh water clams scallops Zebra Mussel Zebras on native clams (Unionidae) mussels oysters ctenidium umbo Adductor Right muscle valve Labial Excurrent palps mouth Incurrent siphons Mantle edge Best understood in the context of their Foot largely sedentary adult life style Ctenidia of Bivalves are modified for feeding except in one group: the Protobranchs Two principal types, distinguished by their Ctenidia and mode of feeding Class Bivalvia Protobranchia Llamellibranchia 1 In most bivalves ctenidia are sheet-like Captured particles are moved to a ciliated ventral with high S.A., and are used for feeding groove and then as a mucus strand to the mouth. http://www.biology.ualberta.ca/facilities/multimedia/index.php?Page=252 Summary of Water Flow and Feeding http://web.uconn.edu/jevanward/video/musselsum.MPG Mussel lamellibranch (filibranch) ctenidium Feeding simulation http://www.biology.ualberta.ca/facilities/multimedia/uploads/zoology/FilibranchBivalve.html The sheetlike, arrangement of ctenidia in most bivalves is known as the Llamellibranch condition Living Cephalopods Squid Architeuthys Giant squid up to Nautilus 20 m long Mesonycheteuthis Colossal squid Cuttlefish up to 14 m major prey item of sperm whales Octopods Dosidicus Humboldt squid, smaller --The class as a whole is adapted for but numerous (2 m) and swimming, suspended in the water by comes to surface to buoyancy mechanisms. feed -- all are carnivores, occupying the same niche as fishes 2 Ammonites Sub Class Nautiloidea 5-6 species remain from diversity in geologic past Live in the last chamber of a multi-chambered shell Move by forcing water Largest is 3 m in through a siphon. diameter Cuttles, Squids and Octopuses Sub Class Nautiloidea How does a Nautilus adjust and maintain its buoyancy in water? -tendency is reduction of shell. - compensated for by selective ionic control; accumulate ammonium - other adaptations to shell loss and life style Specifically, compensation takes the following forms: cuttle Stealth and other defenses chameleons of the sea Acute sensory structures Speed Cunning most specialized, agile and cryptic octopus 3 A. Stealth and other defenses A. Stealth and other defenses Chromatophores: each cell contains a different pigment which may be red, orange, brown, black, yellow or blue Ink Sack : ink with melanin and mucus also dopamine, L-DOPA, tyrosinase Pseudomorphs Cephalopod Chromatophore Cephalopod Skin Papillae 9/16/2004 11:42 AM The most well known of these cells is the chromatophore. Chromatophores are groups of cells that include an elastic saccule that holds a pigment, as well as 15-25 muscles attached to this saccule (Hanlon and Messenger 1996). These cells are located directly under the skin of cephalopods. When the muscles contract, they stretch the saccule allowing the pigment inside to cover a larger surface area. When the muscles relax, the saccule shrinks and hides the pigment. Unlike other animals, the chromatophores in cephalopods are neurally controlled, with each chromatophore being attached to a nerve ending (Messenger 2001). In some squid, each chromatophor muscle is innervated by 2 to 6 nerves that directly link to the animals brain (Messenger et al 2001). In this way the animal can increase the size of one saccule while decreasing the size of another one right next to it. This allows the cephalopods to produce complex patterns (Messenger 2001, Messenger et al 2001), such as the zebra stripes seen in aggressive displays by male cuttlefish. The speed at which this can be controlled allows the animal to manipulate these patterns in a way that makes them appear to move across the body. In some species of cuttlefish, it has been noted that while hunting, the cuttlefish may produce a series of stripes that move down their bodies and arms. Some scientists have suggested that this could be used to mesmerize prey before striking, but the purpose of this behavior has yet to be proven. The pigments in chromatophores can be black, brown, red, orange or yellow. They are not responsible for producing the blue and green colors seen in some species. Interestingly, many deep water forms possess fewer chromatophores as they are less useful in an environment in little or no light. Figure 2. A) Chromatophores on skin of Loligo. (CephBase image No. 280 by Roger T. Hanlon) B) Chromatophores visible on Lolliguncula brevis (CephBase image No. 263 from UTMB). Iridophores are found in the next layer under the chromatopphores (Hanlon et al 1990, Cooper et al 1990). Iridophores are layered stacks of platelets that are chitinous in some species and protein based in others. They are responsible for producing the metallic looking greens, blues and golds seen in some species, as well as the silver color around the eyes and ink sac of others (Hanlon and Messenger 1996). Iridophores work by reflecting light and can be used to conceal organs, as is often the case with the silver coloration around the eyes and ink sacs. Additonally they assist in concealment and communication. Previously, it was thought that these colors were permanent and unchanging unlike the colors produced by chromatophores. New studies on some species of squid suggest that the colors may change in response to changing levels of certain hormones (Hanlon et al 1990, Cooper et al 1990). However, these changes are obviously Black, brown, orange or yellow colors slower than neurally controlled chromatophore changes. Iridophores can be found in cuttlefish, some squid and some species of octopus. Also iridiophore reflective cells Most cephalopods are completely colorblind neurophilosophy.files.wordpress.com B. Acute sensory structures C. Speed -- Vision -- Lateral line analogs Rival fish in ability to swim, attaining burst speeds of 5-10 m second sustained for short distances at speeds of up to 40 km hr. Burst speed is achieved by jet propulsion More gradual swimming is fin undulation 4 C. Speed : complex nerve control C. Speed : circulatory system of locomotion Hearts Requires a closed, elaborate circulatory system Assures synchronized contraction of mantle muscles D. Cunning Experiments with Octopus vulgaris show their ability to learn. They learn to choose colors not associated with shock. Observers choose properly colored objects after -- Relative to body size, the watching demonstrators brain is larger than that of most fish 5 .