bio 191 - ch 26 - pt 2

26.6

lophotrochozoa: the flatworms, rotifers, bryozoans, brachiopods, mollusks, and annelids

lophotrochozoa

all possess:

• a lophophore - feeding structure

• trochophore - swimming larval stage

phylum platyhelminthes - flatworms with no coelom

among the first animal predators

acoelomate, likely the first bilateral animals to develop 3 distinct germ layers

• lack specialized respiratory or circulatory systems; rely on diffusion (can’t pump blood against gravity)

• Food is digested in a gastrovascular cavity 

• Reproduction is sexual or asexual 

platyhelminthes are organized into 4 classes 

flatworms lifecycles can be complex

An individual adult fluke can produce 360 million offspring during its lifetime

phylum Rotifera - have a pseudocoelom and ciliated crown

have an alimentary canal, a digestive tract with a separate mouth and anus

bryozoa and brachiopoda both possess a lophophore (ciliary feeding device) and a true coelom 

Bryozoans are small (0.5mm) colonial animals 

Brachiopods are small (1-8 cm), bottom-dwelling marine organisms that have 2 shell halves

phylum mollusca

Mollusks have a soft body, often protected by a shell

The tremendous diversity of mollusk body plans is related to environmental diversity

all molusks have 3 major body sections

1. muscular foot 

2. visceral mass

3. mantle 

mollusks typically have an open circulatory system

with a heart that pumps body fluid (hemolymph) through vessels and into cavities called sinuses

most mollusks have separate sexes,

Though some are hermaphroditic

• the 780 species of cephalopods are the most complex mollusks

  • A closed circulatory system where blood flows entirely within a series of vessels

phylum annelida - the segmented worms

Segmentation confers at least 3 major advantages

• Repetition provides backup 

• more effective locomotion 

• Some segments can be specialized 

Phylum Annelida - the segmented worms

• sexual reproduction involves two individuals

  • some species reproduce asexually by fission 

• double transport system: both the circulatory system and the coelomic fluid carry nutrients, wastes, and respiratory gases 

• Respiration occurs directly through the permeable skin surface 

26.7

Ecdysozoa: the nematodes and arthropods

ecdysozoa: nematodes and arthropods

• All have a cuticle, a nonliving cover such as an exoskeleton that supports and protects the animal 

• variety of appendages for locomotion (wings, legs) evolved in many species 

• internal fertilization 

• many undergo metamorphosis 

Phylum Nematoda - small pseudocoelomate worms covered by a tough collagen cuticle 

• Nematodes (roundworms) range from 1mm to 5 cm

• found from the poles to the tropics in soil. fresh and marine water, as well as inside plants and animals as parasites

• , reproduction is usually sexual with separate males and females, fertilization is internal 

• body plan: gases diffuse across the cuticle, pseudocoelom, complete digestive tract

a large number of nematodes are

parasitic in vertebrates

phylum arthropoda - spiders, millipedes, centipedes, insects, and crustaceans 

Most successful phylum - ¾ of all species are arthropods 

important features 

• exosekeleton 

• segments and jointed appendages, tagmata 

• cephalization

• open circulatory system 

• Cuticle blocks diffuse gases 

  • tracheal system with spiracles

arthropod classification is complex and ongoing

5 main subphyla

• trilobita - extinc 

• chelicerata 

• myriapoda

• hexapoda

• crustacea 

Arthropoda: subphylum: Chelicerata

all species have a body with 2 tagmata

4 pairs of walking legs (8 legs total)

Arthropoda subphylum: myriapoda 

millipedes have two pairs of legs per segment 

• slow-moving herbivores 

centipedes have one pair of walking legs per segment 

• fast-moving carnivores

Arthropoda subphylum: Hexapoda

insects and relatives

• have 3 tagmata (head, thorax, and abdomen) and 3 pairs of walking legs 

insect body plan

• wings developed as an outgrowth of the body wall cuticle

insect diversity

there are 35 different orders (some have over 100,000 species)

hexapoda

all insects ave separate sexes and use internal fertilization

4 stages of complete metamorphosis 

• egg

• larval

• pupa

adult 3 stages of incomplete metamorphosis 

• egg

• nymph

• adult

subphylum crustacea

crabs, lobsters, barnacles, and shrimp

crustacean body plan

• 2 pairs of antenna

• cephalothorax and abdomen

open circulatory system

crustacean diversity

Common clades include shrimp-like krill, isopods like the terrestrial pill bug, and decapods such as crabs and lobsters

26.8

Deuterostomia: the echinoderms and chordates

phylum echinodermata

all display modified radial symmetry

• free-swimming larvae have bilateral symmetry; radial symmetry is present only in sedentary adults 

Most exhibit autonomy, the ability to regenerate from a detached body part (limb) 

echinoderm body plan 

Most have an exoskeleton, and they have a true coelom 

The water vascular system functions in movement, gas exchange, feeding, and excretion 

5 main classes of echinoderm exist today

• sea stars

• brittle stars

• sea urchins, sand dollars

• sea lilies, feather stars

• sea cucumber 

phylum chordata - includes all vertebrates and some invertebrates

4 critical innovations of all chordates

1. notochord 

2. dorsal hollow nerve cord 

3. pharyngeal slits

4. postanal tail 

all chordates exhibit these characteristics at some life stage 

the phylum chordata contains 

• subphylum cephalochordate 

• subphylm urochordata 

• subphylum vertebrata 

cephalochrodata - the lancelets

have all 4 chordata characteristics

urochordata - the tunicates

larval tunicate displays all 4 chordate

An adult only displays pharyngeal slits