Arthropods: Animals with Jointed Appendages

10. Arthropods: Animals with Jointed Appendages • Phylum Arthropoda = 75% of species • Have exoskeleton—a hard, protective exterior skeleton composed of protein and chitin (a tough polysaccharide) • molting—shedding and replacement of exoskeleton to permit animal’s growth • Body is divided into segments • Usually, each segment has a pair of jointed appendages, for locomotion, mouthparts, sensation, ornamentation • Have highly developed nervous systems • sophisticated sense organs • capacity for learning • 2 major groups of marine arthropods: • chelicerates – have a pair chelicerae (oral appendages) and lack mouthparts for chewing food • mandibulates – have appendages called mandibles that can be used to chew food

11. Arthropods: Animals with Jointed Appendages • Have highly developed nervous systems • sophisticated sense organs • capacity for learning • 2 major groups of marine arthropods: • chelicerates – have a pair chelicerae (oral appendages) and lack mouthparts for chewing food • mandibulates – have appendages called mandibles that can be used to chew food

12. Chelicerates • 6 pairs of appendages; 1 pair are chelicerae for feeding • Horseshoe crabs • 3 body regions • cephalothorax – largest region with the most obvious appendages • abdomen – contains the gills • telson – a long spike used for steering and defense • body is covered by a carapace—a hard outer covering • Horseshoe crabs (continued) • locomotion by walking or swimming by flexing the abdomen • mostly nocturnal scavengers • smaller males attach to females to mate, and eggs are laid in a depression on the beach; larvae return to the sea to grow

13. Chelicerates • Horseshoe crabs (continued) • locomotion by walking or swimming by flexing the abdomen • mostly nocturnal scavengers • smaller males attach to females to mate, and eggs are laid in a depression on the beach; larvae return to the sea to grow

14. Chelicerates • Sea spiders • have small, thin bodies with 4 or more pairs of walking legs • only marine invertebrate known where the male carries the eggs (with an extra pair of appendages) • palps—appendages used in sensation • feed on juices from cnidarians and other soft-bodied invertebrates, using a long sucking proboscis

15. Mandibulates • Crustaceans—marine mandibulates • Crustacean anatomy • 3 main body regions: • head • thorax • abdomen • appendages: • 2 pairs of sensory antennae • mandibles and maxillae used for feeding • walking legs, swimmerets (swimming legs), legs modified for reproduction, chelipeds (legs modified for defense) • gas exchange • small crustaceans exchange gases through their body surface • larger crustaceans have gills • Molting • Crucial part of the life cycle • Frequency of molting decreases with age • Controlled by specific hormones produced in a gland in the head, and initiated by environmental conditions

16. Mandibulates • gas exchange • small crustaceans exchange gases through their body surface • larger crustaceans have gills • Molting • Crucial part of the life cycle • Frequency of molting decreases with age • Controlled by specific hormones produced in a gland in the head, and initiated by environmental conditions

17. Decapods • Order decapoda; includes animals with 5 pairs of walking legs: • crabs • lobsters • true shrimp • 1st pair of walking legs are chelipeds—pincers used for capturing prey and for defense • Wide range in size • Nutrition and digestion • chelipeds are used for prey capture • appendages are used for scavenging • predation and scavenging are usually combined • some decapods are deposit or filter feeders

18. Decapods • Specialized behaviors • hermit crabs inhabit empty shells • decorator crabs camouflage carapaces with bits of sponge, anemones, etc. • common blue crabs are agile swimmers

19. Decapods • Nutrition and digestion • chelipeds are used for prey capture • appendages are used for scavenging • predation and scavenging are usually combined • some decapods are deposit or filter feeders

20. Decapods • Reproduction • sexes usually separate • males have appendages modified for clasping females and delivering sperm • spermatophores—sperm packages • copulatory pleopods—2 pairs of anterior abdominal appendages that deliver sperm • most brood their eggs in chambers or modified appendages

21. Decapods • Reproduction (continued) • larval stages: • zoea larval stage—initial stage in crabs, recognized by the very long rostral spine and sometimes lateral spines (thought to reduce predation) • nauplius larva—initial stage in shrimp

22. Mantis Shrimp • Order Stomatopoda • Highly specialized predators of fishes, crabs, shrimp and molluscs • 2nd pair of thoracic appendages • enlarged • has a movable finger that can be extended rapidly for prey capture/defense • used to spear or smash prey

23. Mantis Shrimp • Reproduction • some mantis shrimp pair for life and share a burrow • zoea larvae hatch from an egg mass • retain planktonic form for 3 months, then settle and take up adult lifestyle

24. Krill • Order Euphausiacea • Pelagic, shrimp-like, 3-6 cm long • Filter feeders that eat zooplankton • Most are bioluminescent • photophore—specialized light organ • swarms—large masses of individuals; bioluminescent is thought to signal swarming behavior • Food source for some whales, seals, penguins, and many fishes

25. Amphipods • Order Amphipoda • Shrimp-like, with posterior 3 pairs of appendages directed backward • Many are burrowers; some construct tubes which they inhabit • Most are detritus feeders or scavengers, some are herbivores • gnathopods—special appendages for picking up plant and animal remains • Eggs fertilized in female’s brood chamber; young resemble adults upon hatching

26. Copepods • Class Copepoda – the largest group of small crustaceans • Usually the most abundant member of the zooplankton • Mostly suspension feeders; some rely on detritus, some are predators • Males fertilize females with spermatophores; eggs are shed into the water column where they hatch

27. Barnacles • Class Cirripedia – the only sessile crustaceans • Most have calcium carbonate shell • Attach directly to a hard surface, or have a stalk for attachment • Filter feed using cirripeds—feathery appendages which extend into the water when the shell is open • Reproduction • hermaphroditic • cross-fertilized using a long, extensible penis • brooded eggs hatch into nauplius larvae • nauplius larvae develop into cyprid larvae, which have compound eyes and a carapace of 2 shell plates • cyprid larvae attach using adhesive glands in antennae, then metamorphose into adults

30. Barnacles • Reproduction • hermaphroditic • cross-fertilized using a long, extensible penis • brooded eggs hatch into nauplius larvae • nauplius larvae develop into cyprid larvae, which have compound eyes and a carapace of 2 shell plates • cyprid larvae attach using adhesive glands in antennae, then metamorphose into adults

31. Ecological Roles of Arthropods • Arthropods as food • important food sources for marine animals and humans • copepods form a link between phytoplankton they eat and many animals that use them as a major food source • krill are consumed in large quantities by whales and other organisms • Arthropods as symbionts • cleaning shrimps remove ectoparasites and other materials from reef fish • some copepods are ectoparasites for fish • some copepods are endoparasites or commensals within polychaete worms, echinoderms, tunicates, bivalves or cnidarians • amphipods carry sea butterflies • barnacles are commensal with many hosts • Role of arthropods in recycling and fouling • grass shrimp feed on detrital cellulose material, and so helps break down algae and grasses in tidal marsh ecosystems • barnacles are a serious fouling problem on ship bottoms • attached barnacles can reduce ship speed by 30% • special paints and other anti-fouling measures

32. Ecological Roles of Arthropods • Arthropods as symbionts • cleaning shrimps remove ectoparasites and other materials from reef fish • some copepods are ectoparasites for fish • some copepods are endoparasites or commensals within polychaete worms, echinoderms, tunicates, bivalves or cnidarians • amphipods carry sea butterflies • barnacles are commensal with many hosts

33. Ecological Roles of Arthropods • Role of arthropods in recycling and fouling • grass shrimp feed on detrital cellulose material, and so helps break down algae and grasses in tidal marsh ecosystems • barnacles are a serious fouling problem on ship bottoms • attached barnacles can reduce ship speed by 30% • special paints and other anti-fouling measures

34. Lophophorates • Lophophorates are sessile animals that lack a distinct head • Possess a lophophore—arrangement of ciliated tentacles that surround the mouth, used for feeding, gas exchange • 3 phyla of lophophorates: • Phoronida (phoronids) • Ectoprocta (bryozoans) • Brachiopoda (brachiopods)

35. Phoronids • Small, worm-like animals • Secrete a tube of leathery protein or chitin that can be attached or buried in bottom sediments • Catch plankton and detritus with mucus-coated tentacles • Can reproduce sexually or asexually (budding, transverse fission) • Have a planktonic larval stage

37. Bryozoans • Small, abundant, colonial animals • Most live on rocks, shell, algae, mangroves, etc. in shallow water • Colonies are composed of zooids (tiny individuals), each inhabiting a box-like chamber it secretes • Most are hermaphroditic brooders • Larvae are planktonic; they settle to form new colonies

39. Brachiopods • Most lamp shells are benthic and live in shallow water • Have mollusc-like, bivalve shells • valves differ in size and shape, and are dorsal and ventral • a pedicle (fleshy stalk) attaches the shell or is buried • Gather detritus/algae with lophophore • Generally have separate sexes; larvae are planktonic and settle in 24-30 hrs.

40. Ecological Roles of Lophophorates • As a group, they are filter feeders • Food for many invertebrates, especially molluscs and crustaceans • Largely responsible for fouling ship bottoms

41. Echinoderms: Animals with Spiny Skins • Phylum Echinodermata • Larval forms exhibit bilateral symmetry but most adults exhibit a modified form of radial symmetry • Mostly benthic, and found at nearly all depths • Sea cucumbers and brittle stars are commonly found in deep-sea samples

42. Echinoderm Structure • Endoskeleton—internal skeleton that lies just beneath the epidermis • ossicles—plates of calcium carbonate • endoskeleton is composed of ossicles held together by connective tissue • Spines and tubercles project outward from the ossicles • pedicellariae—tiny, pincer-like structures around the bases of spines that keep the body surface clean in some echinoderms

43. Echinoderm Structure • Water vascular system—unique hydraulic system that functions in locomotion, feeding, gas exchange and excretion • water enters by the madreporite • passes through a system of canals • attached to some canals are tube feet—hollow structures with a sac-like ampulla within the body and a a sucker protruding from the ambulacral groove

44. Sea Stars • Class Asteroidea • Typically composed of a central disk + 5 arms or rays • On underside, ambulacral grooves with tube feet radiate from the mouth along each ray • Aboral surface—the side opposite the mouth, which is frequently rough or spiny

46. Sea Stars • Feeding in sea stars • most are carnivores or scavengers of invertebrates and sometimes fish • prey are located by sensing of substances they release into the water • sea stars envelope and open bivalves, evert a portion of the stomach, and insert it into the bivalves to digest them • digestive glands located in each ray provide digestive enzymes

48. Sea Stars • Reproduction and regeneration • sea stars can regenerate rays; some can regenerate themselves from a single ray plus part of the central disc • asexual reproduction involves division of the central disk and regeneration of each half into a new individual • most have separate sexes, which shed eggs and sperm into the water for fertilization and hatching into usually planktonic larvae

49. Ophiuroids • Class Ophiuroidea • e.g. brittle, basket and serpent stars • Benthic with 5 slender, distinct arms, frequently covered with many spines • Lack pedicellariae and have closed abulacral grooves • Tube feet lack suckers and are used in locomotion and feeding • Brittle stars shed arms if disturbed