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Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Three Class Cephalopoda 700 extant spp. described Nautiloids, cuttlefish, squids, and octopods Carnivores Fast swimmers that compete with fish Some anatomical / physiological similarities Ecologically similar Most active molluscs The largest invertebrates Architeuthis – 20 m Enteroctopus – 9.6 m arm span Possibly the most intelligent invertebrates Highly developed nervous system Image forming eyes Capable of complex behaviors Body Form Dorsoventral axis of early molluscs elongated Functionally, the ventral aspect of the cephalopods is really the anterior aspect Head and foot are located at the anterior end The name cephalopod means “head foot” Head Houses brain (more later) Mouth Buccal cavity Beak Buccal mass Radula Anterior gut Foot and Visceral Mass Foot is modified to form several appendages that surround the mouth Ventral region of foot also forms tubular siphon (funnel) Arms Tentacles Leads to mantle cavity Visceral Mass Dorsal Elongate Hump shaped Thick and muscular Surrounds visceral mass and mantle cavity Mantle cavity is ventral / anterior; houses: One or two pairs of bipectinate, nonciliated gills Anus w/ ink sac attached • Releases ink which quickly forms a cloud • Confuses predators and can anesthetize chemoreceptors Nephridiopore Gonopore Mantle Shell External in nautiloids Internal in squids and cuttlefish • Gladius or pen • Cuttlebone, respectively Absent in octopods Buoyancy Regulation Nautilus uses its shell Chambers are filled with fluid and then septum forms Gas / water can be pumped in / out of chambers Those without shell use other methods Replace high molecular weight sea water in coelom with low molecular weight ammonium ions Lack of heavy external shell makes buoyancy less of a problem Webbed octopods extend arms to increase SA and retard sinking • Web acts like a parachute Locomotion Important for: Two main types Prey capture Buoyancy regulation Diel vertical migration (DVM) Crawling Swimming Crawling Typical of octopods Locomotion cont… Swimming Bell swimming in webbed octopods Undulations of lateral fins Jet propulsion by ejecting water from mantle cavity • Circular muscle contractions • Water ejected through exhalant siphon • Valve covers inhalant siphon • Propelled in opposite direction • Slow and fast jetting • Flying squids can fly 50 m through air Nutrition Cephalopods are visual predators, so they posses image forming eyes for prey detection (more later) Raptorial Capture using appendages, many of which are covered with suckers May be toothed Tentacles capture and arms manipulate in most cases Beak is made of proteins and chitin Buccal mass is large collection of muscles surrounding beak Radula pulls in pieces of prey that the beak rips off Many have venom glands that empty into buccal cavity Venom and other secretions enter prey’s blood stream through beak wounds Tetrodotoxin from little blue-ringed octopus is responsible for some human deaths Gas Exchange Considered to be concurrent in most cases Ways to supplement gas exchange Large gill SA Some gas exchange across body surface Rapid ventilation Pressurized circulatory system Restricted to cold water, which has higher O2 solubility Circulation Closed system Capillary beds are main sites of diffusion, as opposed to hemocoels Hearts One systemic - body Two branchial - gills Vessels lined with endothelium, as in verts Hemocyanin Excretion Ammonotelic Two nephridia in all but nautiloids (which have four) Nephridia are attached to pericardial cavity of branchial hearts Nervous System Most developed of all inverts, and even rivals some verts Cephalized and bilaterally symmetrical Many ganglia and nerves Some brains are enclosed in a cartilaginous cranium Giant motor neurons for rapid transmission of impulses Image forming eyes Structurally similar to human eye Cannot see in color Can discriminate objects as small as 0.5 cm from 1 m away Other sensory organs Epidermal hair lines • Analogous to lateral lines of fish • Sensitive to water movement and pressure changes Statocysts Chemoreceptors • For taste or smell • May be located on suckers and tentacles All except nautiloids lack osphradia Chromatophores Organs with pigment cells located in dermis Cells contain pigment sacs that are under nervous / muscular control Sacs stretch out and flatten, causing pigment to spread out Used for camouflage or when animal is alarmed Some produce waves of color when making defensive displays Also produce bioluminescence Reproduction Gonochoric Single Gonad Usually copulate but have indirect fertilization Sperm is transferred in form of spermatophore Male often transfers with modified arm known as a hectocotylus Fertilization may be external (sea or mantle cavity) or internal Often have courtship displays Lay large (15mm) yolky eggs with gelatinous capsule Can be free floating or attached Many adults ventilate eggs while brooding Some have direct development Most adults have short lifespan (less than three years) and die after spawning Nautiloids Four species of Nautilus Found in the Indo-Pacific ocean External shell that they can retract into Typically between 100 m – 600 m Leathery hood that acts like an operculum Lack ink sack Lack chromatophores 90 arms Some are mechanosensory and chemosensory Lack suckers Swim backwards Specialize on decapods, especially hermit crabs Two pairs of gills Have osphradia Slightly different circulatory system Not entirely closed No branchial hearts Four nephridia Cuttlefish Sepia is a common genus Not as fast or streamlined as squids Eight arms and two tentacles Swim over ocean bottom feeding on shrimps and crabs Two gills Squids Loligo is a common genus Can obtain greatest swimming speeds of any aquatic invert 40 km / hr Feed on fish, crustaceans, and other squids Two gills Eight arms and two tentacles One of their main predators is the sperm whale Sperm whales reach 20 m in length 14,000 beaks found in the belly of one sperm whale Giant squids Architeuthis Live at depths between 300 m and 600 m Not rapid swimmers Sucker scars found on sperm whales Octopods Octopus is a common genus Two gills Tend to be benthic; often crawl over substrate Typically live in a den Leave to forage Den usually littered with shells of prey items Eight arms; no tentacles Eat a variety of prey items, but clams, snails, and crustaceans dominate Pacific giant octopus Enteroctopus Forages up to 250 m from den Paralyze prey with venom and take back to den Inject with poison and enzymes Some drill holes through shells with radula Feeding ecology is similar to that of spiders