Chapter 33: Invertebrates (Part III)

Ribbon worms

• Cylindrical to flattened and very long
• Most are marine, few freshwater or live in humid terrestrial habitats
• Most range from 10 to 20 cm long
• Lineus Longissius reported to reach 60 meters!

• Lineus Longissimus
• A type of ribbon worm

Nemertean

Cephalization; 2

fluid-filled sac that serves as hydraulic power sources for proboscis

True. aka male and female worms

• Typically sexual reproduction.
• Some asexually via fragmentation but may fragments die and do not form a new animal.

The Annelids

• Segmented worms -ringlike segments
• Brain or cerebral ganglion and sensory organs at anterior
• Many species have eyes(earthworms don't)
• Head and tail develop first then segments form between them
• segments divided by septa
• each segment has pair of excretory organs, a ganglion, and locomotory structure (marine annelid segments also have reproductive organs)
• closed circulatory system
• ventral nerve cord connects ganglia in each segment with another and the brain

Development and function of individual segments or groups of segments can differ

Earthworms!

• Head and tail develop first
• Segments form between them

False, they are!

Closed

By contracting circular and longitudinal muscles against the hydrostatic skeleton.

Bristles that help anchor annelids in substrates so they don't slip when they move

• Class Polychaeta: Polychaetes
• Class Clitellata: Earthworms and Leeches

• Marine worms
• Parapodia-fleshy, paddle-like lateral projections used for swimming, burrowing or crawing
• Parapodia also have important role in gas exchange; in some species they are modified into gill-like structures
• Predatory polychaetes have powerful jaws
• Sedentary tube worms have feathery tentacles for filter feeding as well as gas exchange
• Most polychaetes are gonochoric and fertilization is external
• Palolo worms
• Fertilization>spiral clevage>ciliated mobile trochophore larve>growth to adult

Marine

Fleshy, paddle-like lateral projections used for swimming, burrowing, or crawling

gas exchange, some species have modified them into gill-like structures

External

• Annelids: Polychaetes
• gamete-filled terminal parts considered a delicacy by some South Pacific natives

Earthworms and Leeches

Because they both have a clitellim!

A thickened band on the body that secretes mucus to hold worms together during copulation and to form a cocoon for fertilized eggs to develop.

No! Poly wants a clitellum.

• Head is not well developed
• no parapodia
• few chaetae & project directly from body wall
• Eat their way through soil
• No eyes, but do have light-, chemo-, and touch-sensitive cells
• Hermaphroditic
• Cross-fertilization
• Eggs develop into young worms similar to adults

• Most are freshwater, few are marine, some live in tropical terrestrial areas
• Dorsoventrally flattened
• Hermaphroditic
• Cross-fertilization
• Clitellum only develops during mating season!
• Suckers at both ends of body
• Coelom reduced and not segmented
• no chaete (except one species)
• eat detritus or devour small animals
• some suck blood--secrete anesthetics and hirudin

Antocoagulant

medical leech

• Both have a clitellim
• hemaphroditic
• cross-fertilization

• Earthworms do not have eyes
• Leeches only develop a clitellum during mating season
• Leeches are mainly freshwater

• The Arthropods
• The most successful of all animals
• Two-thirds of all animals are arthropods

• Pollinate crops
• food for humans and other animals
• Damage to crops; insects are voracious herbivores
• Carriers or spreaders of disease to plants and animals including humans

• Class Chelicerata: spiders, mites, ticks, horshoe crabs
• Class Crustacea: crabs, shrimp, lobsters, barnacles, pill bugs
• Class Hexapoda: Insects
• Class Myriapoda: centipedes, millipedes
• Class Triloboita: trilobites (extinct)

Phylum Arhropoda

• Chelicera (pincers) in chelicerates
• Mandibles (biting jaws) in hexapods, crustaceans, and myriapods

• Body segments look alike in some arthropods
• tagmatization: the fusion of segments into specialized functional groups
• Tagmata include: head, thorax, abdomen
• In some arthropods, head and thorax are fused to form a cephalothorax

• fusion of segments into specialized functional groups.
• Includes: head, thorax, abdomen
• Some arthropods: cephalothorax

• Made of chitin and protein
• provides antagonism for muscles, support for body, protection against physical forces
• Can protect against water loss

Chitin and protein

• Size (weight gets too great with increased size)
• Rigidity (must undergo ecdysis or molting)

• May be modified into antennae, various kinds of mouthparts, legs
• Can bend to extend or retract
• Joints serve as fulcrum for appendage movement so leverage is possible

• Open circulatory system
• Heart pumps blood anteriorly
• Blood flows towards posterior through spaces between tissues, when heart relaxes blood returns to posterior region of heart through one-way valves.

• Double chain of segmented ganglia along ventral surface
• three fused ganglia form brain
• functions such as eating, moving, copulation, can be carried out even when brain is removed.
• compound eyes composed of ommatidia (individual visual units)
• ocelli= simple eyes present in some arthropods

Individual visual units that form compond eyes in arthropods.

Simple eyes present in some arthropods

• Gills: in marine crustaceans
• book gills: horseshoe crabs
• outer epithellium or gut for gas exchange: in some tiny arthropods
• Trachea: in terrestrial arthropods; tracheae branch into tracheoles
• Spiricles: openings in exoskeleton where air enters, can be closed to prevent water loss
• Book lungs: in many spiders

• Book gills: horseshoe crabs
• Book Lungs: spiders

openings in exoskeleton where air enters; they can be closed to prevent water loss

• In aquatic arthropods, waste diffises from blood in gills
• Malpighian tubules occur in terrestrial insects, myriapods, and chelicerates

• Occur in terrestrial insects, myriapods, chelicerates
• slender projections from digestive tract
• attached at junction of midgut and hindgut
• tubules contain fluid, are nitro-genous wastes from blood that bathes tubules
• precipitated as uric acid or guanine that are then emptied into hindgut for elimination
• water and salts are reabsorbed by hindgut and returned to arthropod's body
• Key adaptation to life on land

Malpighian tubules

Spiders, mites, ticks, scorpions, daddy long-legs, horseshoe crabs

• Two tagmata (body sections)
• Pair of chelicera (fangs or pincers)
• Pair of pedipals
• foud pairs of walking legs
• mostly carnivorous, but mites are mostly herbivorous

• Two tagmata
• The anterior prosoma bears all appendages and opisthosoma

• copulatory organs in male spiders
• large pincers in scorpions
• sensorial in most other chelicerates

• Order Araneae: Spiders
• Order Acari: Mites and Ticks

• Spiders
• From phylum Chelicerate
• Important as predators of insects
• produce silk that is forced out of spinnerets
• all spiders have poison glads with channels through their chelicerae
• poison/venom paralyzes prey

hunt

black widows and brown recluse

• Mites and Ticks
• found in every habitat
• predators and parasites of various organisms
• most mites less than 1 mm long
• in mites, cephalothorax and abdomen fused into ovoid body
• Respiration using tracheae or directly through body surface
• ticks are blood-sucking parasites of humans and other animals

Mites; ovoid

• Rocky Mountain spotted fever
• Lyme disease
• Red-water fever (affects cattle, horses, sheep, and dogs)

• Three tagmata= cephalon, thorax, and adbomen
• Two pairs of antennae (crustaceans are the only arthropods)
• Three pairs of appendages for chewing and manipulating food
• vairous pairs of legs (located on abdomen and thorax)
• Crustacean appendages are biramous("two-brached")
• large crustacean have feathery gills for respiration
• Gas exchange in smaller crustaceans occurs directly through thin regions of cuticle or through entire body

Crutaceans

• Gonochoric (except barnacles)
• Characteristic naupilus larva with three pairs of appendages
• nauplius is evidence for single common ancestor

• "Decapod" means ten feet
• shrimp, lobsters, crabs, crayfish

• five pairs of thoracic appendages
• calcium carbonate reinforced exoskeleton
• cephalothorax covered by carapace
• pincers used for obtaining food
• swimmerates on ventral surface of abdomen in lobsters and crayfish
• Uropods are paired flattened appendages at posterior that form a paddle
• Telson- tail pipe
• uropods and telson push water anteriorly, propelling animal posteriorly

found on the ventral surface of abdomen in lobsters and crayfish

paired flattened appendages at posterior that form a paddle

Tail spine in decapods

• Uropods and telson; anteriorly
• this propels the animal posteriorly

barnacles

• Sessile adults, but nauplius larva is mobile
• adults are filter-feeders; sweep legs through water in order to gather small food particles
• Hermaphroditic condition is thought to be related to their sessile lifestyle
• Have the longest penis relative to their size; allows sessile animals to cross-fertilize

Barnacles; allows sessile animals to cross fertilize.

• The Insects
• largest group of animals in terms of number of species and number of individuals
• found in every habitat on land and in freshwater; few found in the sea

• Digestive tract is tube about same length as body in many
• digestion occurs in stomach or midgut
• Malpighian tubules for excretion
• trachea for gas exchange
• spiracles are openings between segments along side of abdomen and thorax where air enters

coiled

• Eyes
• Sensory setae sensative to mechanical and chemical stimuli; numerous on antennae and legs
• tympanum: thin membrane that acts like eardrum, detects sound waves and vibrations
• pheromones are chemicals released by insects for communicating mating signals, trail markers, etc.

• Metamorphosis: change in form
• simple metamorphosis: eggs>nymph stages>adult
• Complete metamorphosis: egg>larva>pupa(chrysalis)>final molt into adult or imago.

Complete metamorphosis includes a pupa(chrysalis) stage.

Centipedes and Millipedes

• Both have head followed by numerous segments
• both are gonochoric
• fertilization is internal
• all lay eggs

• Centipedes
• One pair of legs per segment
• some centipedes hatch with a final number of legs; others add legs after hatching
• carnivorous
• poison fangs

Tend to care for their young, a rather uncommon behavior among invertebrates

• Millipedes
• two pairs of legs per segment
• Herbivorous
• roll into flat coil or sphere for defense
• glands produce foul-smelling fluid
• some produce cyanide gas

Millipedes

The centipede

• Centipedes: carnivorous
• Millipedes: herbivorous

• "Spiney skin"
• Exclusively marine
• Deuterostome development (only other phylum beside vertebrates)
• Endoskeleton of calcium carbonate plates
• Pentaradial symmetry (parts of 5)
• water-vascular system aids in movement and feeding
• larva have bilateral symmetry

• Echioderms have pentaradial symmetry but larvae is bilateral
• thought to have evolved from bilaterally symmetrical ancestors.

Towards the substrate

Away from substrate

Sea cucumbers

• horizontal axis
• surface faces forward

• Ossicles = calcium carbonate plates that make up endoskeleton
• Depending on the class, ossicles may be more loosely arranged, tightly fit together to form a test, or scattered throughout the body. 
• mutable callagenous tissue can change texture from tough and rubbery to fluid in seconds if animal is disturbed.

Cast off body parts

• Radially organized
• Madreporite
• WVS extends out into each arm of a sea star
• Ampulla allows tube foot to extend or contract
• gas exchange occurs across body surface and the tube feet.

water enters through the anus

Structure on aboral(away from the mouth) surface where water enters Echinoderms

The bulb that allows tube feet in echinoderms to extend or contract

• Many echinoderms can regenerate body parts
• Sexual reproduction is the norm
• gonochoric
• fertilization is external
• larvae are bilateral
• Each class of echinoderm has a characteristic larva

Asteroids and ophiuroids

Holothuroidians (sea cucumber)

True

• Asteroidea
• Ophiroidea
• Echinoidea
• Holothuroidea
• Crinidea

• Sea Stars
• Orginized in parts of five or multiples of five
• predators

• Brittle stars
• Arms are slender and "snake-like"
• Arms join central disk very abruptly
• tube feet for feeding not locomotion
• brittle stars have no anus

• Sea urchins and sand dollars
• no arms
• five double rows of tube feet extend through calcareous test (shell)
• Spines are moveable and have a ball-and-socket joint

• Sea Cucumbers
• Oriented horizontally to substrate
• Parts of five
• Filter feeders
• Have repiratory tree
• If skin is rubbed, can go from rigit to liquid in a couple minutes

• Sea lilies and feather stars
• oral surface faces up
• filter feeders

Ophiuroidea: Brittle Stars

Class Echinoidea: sea urchins and sand dollars