Biology 320 Invertebrate Zoology Fall 2005

1. Biology 320Invertebrate ZoologyFall 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 • Ecologically similar • Most active molluscs

3. 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

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”

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

6. Foot and Visceral Mass • Foot is modified to form several appendages that surround the mouth • Arms • Tentacles • Ventral region of foot also forms tubular siphon (funnel) • Leads to mantle cavity • Visceral Mass • Dorsal • Elongate • 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 • Anus w/ ink sac attached • Releases ink which quickly forms a cloud • Confuses predators and can anesthetize chemoreceptors • Nephridiopore • Gonopore

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

9. 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

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

11. 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

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 • 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 • 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 • Some gas exchange across body surface • Rapid ventilation • Pressurized circulatory system • Restricted to cold water, which has higher O2 solubility

15. 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

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 • 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

18. 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

19. 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

20. 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

21. 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

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

23. 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

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 • 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 • 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

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 • 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 • 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