1. Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Three

2. Class Cephalopoda  700 extant spp. described  Nautiloids, cuttlefish, squids, and octopods  Carnivores  Fast swimmers that compete with fish Some anatomical / physiological similarities Some anatomical / physiological similarities Ecologically similar Ecologically similar  Most active molluscs

3.  The largest invertebrates Architeuthis – 20 m Architeuthis – 20 m Enteroctopus – 9.6 m arm span Enteroctopus – 9.6 m arm span  Possibly the most intelligent invertebrates Highly developed nervous system Highly developed nervous system Image forming eyes Image forming eyes Capable of complex behaviors Capable of complex behaviors

4. 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” The name cephalopod means “head foot”

5. Head  Houses brain (more later)  Mouth  Buccal cavity Beak Beak Buccal mass Buccal mass Radula Radula  Anterior gut

6. Foot and Visceral Mass  Foot is modified to form several appendages that surround the mouth Arms Arms Tentacles Tentacles  Ventral region of foot also forms tubular siphon (funnel) Leads to mantle cavity Leads to mantle cavity  Visceral Mass Dorsal Dorsal Elongate Elongate Hump shaped Hump shaped

7. Mantle  Thick and muscular  Surrounds visceral mass and mantle cavity  Mantle cavity is ventral / anterior; houses: One or two pairs of bipectinate, nonciliated gills One or two pairs of bipectinate, nonciliated gills Anus w/ ink sac attached Anus w/ ink sac attached Releases ink which quickly forms a cloudReleases ink which quickly forms a cloud Confuses predators and can anesthetize chemoreceptorsConfuses predators and can anesthetize chemoreceptors Nephridiopore Nephridiopore Gonopore Gonopore

8. Shell  External in nautiloids  Internal in squids and cuttlefish Gladius or penGladius or pen Cuttlebone, respectivelyCuttlebone, respectively  Absent in octopods

9. Buoyancy Regulation  Nautilus uses its shell Chambers are filled with fluid and then septum forms Chambers are filled with fluid and then septum forms Gas / water can be pumped in / out of chambers 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 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 Lack of heavy external shell makes buoyancy less of a problem Webbed octopods extend arms to increase SA and retard sinking Webbed octopods extend arms to increase SA and retard sinking Web acts like a parachuteWeb acts like a parachute

10. Locomotion  Important for: Prey capture Prey capture Buoyancy regulation Buoyancy regulation Diel vertical migration (DVM) Diel vertical migration (DVM)  Two main types Crawling Crawling Swimming Swimming  Crawling Typical of octopods Typical of octopods

11.  Locomotion cont…  Swimming Bell swimming in webbed octopods Bell swimming in webbed octopods Undulations of lateral fins Undulations of lateral fins Jet propulsion by ejecting water from mantle cavity Jet propulsion by ejecting water from mantle cavity Circular muscle contractionsCircular muscle contractions Water ejected through exhalant siphonWater ejected through exhalant siphon Valve covers inhalant siphonValve covers inhalant siphon Propelled in opposite directionPropelled in opposite direction Slow and fast jettingSlow and fast jetting Flying squids can fly 50 m through airFlying squids can fly 50 m through air

12. 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 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

13.  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 Venom and other secretions enter prey’s blood stream through beak wounds  Tetrodotoxin from little blue-ringed octopus is responsible for some human deaths

14. Gas Exchange  Considered to be concurrent in most cases  Ways to supplement gas exchange Large gill SA Large gill SA Some gas exchange across body surface Some gas exchange across body surface Rapid ventilation Rapid ventilation Pressurized circulatory system Pressurized circulatory system Restricted to cold water, which has higher O 2 solubility Restricted to cold water, which has higher O 2 solubility

15. Circulation  Closed system  Capillary beds are main sites of diffusion, as opposed to hemocoels  Hearts One systemic - body One systemic - body Two branchial - gills Two branchial - gills  Vessels lined with endothelium, as in verts  Hemocyanin

16. Excretion  Ammonotelic  Two nephridia in all but nautiloids (which have four)  Nephridia are attached to pericardial cavity of branchial hearts

17. 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 Some brains are enclosed in a cartilaginous cranium  Giant motor neurons for rapid transmission of impulses  Image forming eyes Structurally similar to human eye Structurally similar to human eye Cannot see in color Cannot see in color Can discriminate objects as small as 0.5 cm from 1 m away Can discriminate objects as small as 0.5 cm from 1 m away

18.  Other sensory organs Epidermal hair lines Epidermal hair lines Analogous to lateral lines of fishAnalogous to lateral lines of fish Sensitive to water movement and pressure changesSensitive to water movement and pressure changes Statocysts Statocysts Chemoreceptors Chemoreceptors For taste or smellFor taste or smell May be located on suckers and tentaclesMay be located on suckers and tentacles All except nautiloids lack osphradia All except nautiloids lack osphradia

19. Chromatophores  Organs with pigment cells located in dermis Cells contain pigment sacs that are under nervous / muscular control Cells contain pigment sacs that are under nervous / muscular control Sacs stretch out and flatten, causing pigment to spread out Sacs stretch out and flatten, causing pigment to spread out Used for camouflage or when animal is alarmed Used for camouflage or when animal is alarmed Some produce waves of color when making defensive displays Some produce waves of color when making defensive displays  Also produce bioluminescence

20. Reproduction  Gonochoric  Single Gonad  Usually copulate but have indirect fertilization Sperm is transferred in form of spermatophore Sperm is transferred in form of spermatophore Male often transfers with modified arm known as a hectocotylus Male often transfers with modified arm known as a hectocotylus  Fertilization may be external (sea or mantle cavity) or internal  Often have courtship displays

21.  Lay large (15mm) yolky eggs with gelatinous capsule Can be free floating or attached 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

22. Nautiloids  Four species of Nautilus  Found in the Indo-Pacific ocean Typically between 100 m – 600 m Typically between 100 m – 600 m  External shell that they can retract into Leathery hood that acts like an operculum Leathery hood that acts like an operculum Lack ink sack Lack ink sack Lack chromatophores Lack chromatophores  90 arms Some are mechanosensory and chemosensory Some are mechanosensory and chemosensory Lack suckers Lack suckers

23.  Swim backwards  Specialize on decapods, especially hermit crabs  Two pairs of gills  Have osphradia  Slightly different circulatory system Not entirely closed Not entirely closed No branchial hearts No branchial hearts Four nephridia Four nephridia

24. 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

25. Squids  Loligo is a common genus  Can obtain greatest swimming speeds of any aquatic invert 40 km / hr 40 km / hr  Feed on fish, crustaceans, and other squids  Two gills  Eight arms and two tentacles

26.  One of their main predators is the sperm whale Sperm whales reach 20 m in length Sperm whales reach 20 m in length 14,000 beaks found in the belly of one sperm whale 14,000 beaks found in the belly of one sperm whale  Giant squids Architeuthis Architeuthis Live at depths between 300 m and 600 m Live at depths between 300 m and 600 m Not rapid swimmers Not rapid swimmers Sucker scars found on sperm whales Sucker scars found on sperm whales

27. Octopods  Octopus is a common genus  Two gills  Tend to be benthic; often crawl over substrate  Typically live in a den Leave to forage Leave to forage Den usually littered with shells of prey items Den usually littered with shells of prey items  Eight arms; no tentacles  Eat a variety of prey items, but clams, snails, and crustaceans dominate

28.  Pacific giant octopus Enteroctopus Enteroctopus Forages up to 250 m from den Forages up to 250 m from den Paralyze prey with venom and take back to den Paralyze prey with venom and take back to den Inject with poison and enzymes Inject with poison and enzymes Some drill holes through shells with radula Some drill holes through shells with radula Feeding ecology is similar to that of spiders Feeding ecology is similar to that of spiders