Protosomes

Animals

Heterotrophs

 ingest food and digest w/ enzymes

Ectoderm

outermost layer

• Becomes: skin & nervous system

Endoderm - (yellow) innermost layer

Becomes: gut, liver, lungs

Mesoderm - (red)

middle layer

• Becomes: skeleton, heart, kidney, muscle, blood

In all animals except sponges, the embryo becomes

layered through the process of gastrulation .  Layers = germ layers 

Acoelomate

No body cavity

Pseudocoelomate

body cavity between mesoderm and endoderm organs attached at mouth & anus

Coelomate

Body cavity completely linedwith mesoderm

Purposes of a Coelom
(or to a lesser extent, a pseudocoelom) 

1. Fluid within the body cavity cushions suspended organs (prevents internal injury)

   • The inner and outer layers of mesodermal tissue (mesentary) suspend the internal organs

2. Allows internal organs to grow and move independently of the outer body wall

Deuterostomes (Superphylum Deuterostomia)

Echinodermata, Hemichordata, and Chordata

Protostomes are themselves classified into two separate Superphyla:

• Ecdysozoa (Arthropoda, Nematoda, and several other phyla)

• Lophotrochozoa (Mollusca, Annelida, Brachiopoda, Platyhelminthes, and many many more phyla)

Deuterostome blastopore

becomes anus at bottom

Protostome coelom formation

• formation is schizocoelous

  • The body cavity forms when the mesodermal tissue “splits.”

Deuterostome coelom formation

•  formation is enterocoelous

  • The body cavity forms when pockets of the primitive gut (archenteron) bud off.

Protostome cell fate

• Determinate – Cells are pre-programmed 

Deuterostome cell fate

indeterminate- cells are stem cells

Ecdysozoa

• First of the two MAJOR branches (Superphyla) of the protostomes

• Ecdysis (molting) – all members of this clade shed their outer body covering

• Reduced cilia

• More ecdysozoan species than all other animals combined!

Phylum Nematoda (Roundworms)

Pseudocoelom

vermiform (worm shape)

complete digestive tract

ventral & dorsal nerve cords

tough cuticle

longtitudinal muscles

dioecious

Vinegar Eels
Nematoda

• Turbatrix aceti

• Free living

• Feed on bacteria & yeas

Trichinella

nematoda

• Parasitic

• Responsible for trichinosis

• From eating infected pork

• Makes cysts in muscle tissues of pigs

• Makes cysts in human brains, too

Ascaris (Nematoda)

• Tropical intestinal parasites

• Females can lay 200,000 eggs+ per day

• Eggs can survive preservation for up to 5 years

• Infection starts when eggs are ingested… thankfully, we no longer do this dissection

Phylum Arthropoda

• Most numerous and diverse group of animals

• From the Greek arthro (joint) + podos (foot)

• Characteristics:

  • Jointed Appendages

  • Segmented Body (Convergent with Annelid worms and Vertebrates)

  • Coelom becomes part of open circulatory system (hemocoel) with hemolymph for blood

  • Exoskeleton composed of Chitin

  • Dioecious

  • Ventral nerve cord

  • Cephalized ganglia (=brain

Subphylum Myriapoda (Arthropoda)

• MANY legs

• Single pair of antennae

• Single pair simple ocelli

• 3 pairs of modified appendages     for mouthparts

• Breathe with spiracles and   tracheae

Centipedes (Class Chilopoda)

• Carnivorous

• 1 pair of legs per segment

• Possess Poison Fangs

Millipedes (Class Diplopoda)

• Herbivorous

• 2 pair of legs per segment – each segment is 2 segments fused together

Subphylum Chelicerata

• Possess Chelicerae

  • Used as pincers or fangs

• Possess Pedipalps

  • Accessory appendages beside the mouth

• No antennae or mandibles

• 3 or 4 pairs of ocelli

• 2 Body Regions

  • Cephalothorax & Abdomen

• 6 pairs of appendages in total

  • 4 pairs of legs, 1 set of chelicerae, 1 set of pedipalps

• Breathe using Gills or Book Lungs

• Often have vestigial tracheae network

Pancrustacea (unranked taxon) (Arthropoda)

• Hexapoda and Crustacea are more closely related than any other two subphyla within the Arthropoda

• Molecular studies support this as a monophyletic clade

• Synapomorphies between Hexapods and Crustaceans: 

  • Heavily segmented

  • Compound Eyes

  • Well-developed mandibles

3 clearly distinguished body regions:

Pancrustacea: Subphylum crustacea (Arthropoda)

• Crabs, Lobsters, Crayfish, Barnacles, Shrimp, Isopods, Branchiopods, etc. (many more)

• Most marine, some freshwater, a few terrestrial

• 2 pairs of sensory antennae

• Each body segment has 2 appendages: antennae, mouth parts, chelipeds, legs, swimmerets, and tail fins

• >3 pairs walking legs

• Biramous (branched) appendages

• Gills or “branchiostegal lungs” for respiration

Lophotrochozoans (spiralia)

• The other MAJOR branch (a.k.a. Superphylum) of protostomes

• Very diverse clade with around 10-15 phyla 

• 4 defining features found in many, but not in all:

  • Increased cilia

  • Many (not all) have Spiral Cell Division/Cleavage in their embryos

  • Lophophore (Lophophorates)

  • Trochophore (Trochozoans)

• Lophophore (Lophophorates

– crown of ciliated tentacles that surround the mouth used for feeding 

• Trochophore (Trochozoans)

• ciliated larval stage of Annelids and Molluscs, some others

Subphylum Rotifera

• Wheel animals

• Part of Phylum Syndermata

• Corona is a two-part ciliated structure around the mouth

• Complete digestive tract

• Pseudocoelomate

• Foot and Toe to attach to surfaces

Phylum Platyhelminthes (flatworms)

• Flat bodies

• Acoelomate

• Hermaphroditic

• First example of cephalization (development of  a head) in the fossil record

• Ladder-like nervous system

• No circulatory system

• Incomplete digestive tract (if present) is large and branching

Phylum Platyhelminthes (Turbellaria)

• Planarians

• Free-living predators or scavengers

• Have protonephridia (flame cells) used for osmoregulation

• “Eyespots” - photoreceptive neurons (a.k.a. ocelli)

• Protrusible pharyx used for eating and voiding feces

Phylum Platyhelminthes (Trematoda)

• Flukes 

• Internal parasites

• Very complex life cycle with 

    multiple hosts (up to 7!)

• Definitive host is almost always a vertebrate

• Have two suckers (oral and ventral) that attach to their host

• Example: Clonorchis sinensis – Chinese liver fluke

Phylum Platyhelminthes (Cestoda)

• Tapeworms

• Internal Parasites

• Definitive host is a vertebrate

• No digestive system-Why?

• Attachment organ called a scolex

  • Not its head – it doesn’t have one!

Proglottids (Platyhelminthes)

 reproductive segments, break off end of worm when fully mature

Trochozoans:

annelida

segmented worms

trcophore larval stage

• Segmented body (convergent with Arthropods and Vertebrates)

• Truly segmented body cavity (divided by septa) with complete gut

• Closed Circulatory System

  • Convergent with Vertebrates & Cephalopod Molluscs

• Cerebral ganglion &  Ventral nerve cord

• Two major clades within Annelida: Errantia & Sedentaria

Phylum Annelida
Class Errantia

• Formerly Polychaetes

• From the Latin Errere, to wander 

• Free-living mobile marine worms

• Largest group of Annelids

• Possess a pair of fleshy parapodia with tiny, chitinous chaetae a.k.a. setae (bristles) on each segment

• Possess well-developed sense organs

  • Antennae & Eyes!

Phylum Annelida
Class Sedentaria

• Sedentary marine Tubeworms, Earthworms, and Leeches

• Possess few to no setae (bristles) and (often) a clitellum

  • Glues them together while mating

  • Secretes cocoon around eggs

Phylum Mollusca

• From the Latin molluscus (soft)

• Mostly marine

• Have a trochophore larval stage

• Characteristics:

  • Foot

    • Movement and food capture

  • Visceral Mass

    • Contains the organs – complete gut

  • Mantle

    • Secretes shell (usually)

  • Radula

    • Scrapes food

    • Found in 3 of 4 major clades

  • Open Circulatory System

    • No blood vessels except heart

Found in 3 of 4 major clades

Phylum Mollusca- polyplacophora

• Chitons

• From the Greek poly (many) + plak (plate) + phoros  (to bear)

• Segmented Shell (8 Plates) does NOT represent true segmentation

• Scrapes algae off rocks with a radula

Phylum Mollusca

Gastropoda

• Slugs, Snails, and their relatives

• From the Greek gaster (gut) + podos (foot)

• Many exhibit torsion: 180 degree rotation of the visceral mass

• 2 or 4 sensory tentacles with eyes on head

• Many have shells

• Most have radulas

Phylum Mollusca- Bivalvia

• From the Latin bis (twice) + valva (leaf or shell)

• Clams, Oysters, Scallops, & Mussels

• Protected between two hinged valves (Left and Right)

• Incurrent & excurrent siphons

• Lost radula

• 4 oversized gills (ctenidia) for respiration and filter-feeding

Phylum Mollusca- cephalopda

• From the Latin cephalic (head) + podos (foot) - modified foot forms part of the siphon and arms/tentacles in the head region

• Chambered Nautilus, Squid, and Octopus

• All are predators

• The most advanced invertebrates:

1. Closed circulatory system with 3 hearts – dual circuit circulation

2. Well-developed eyes

3. Most intelligent invertebrates

4. Dioecious

Chromatophores (cephalopoda)

• pigmented cells that help these animals change color

  • Communication and camouflage

Pen is remnant of shell

•  is internal – found in Squid 

• Octopuses have no pen

• Keratinized beak

• ALL octopuses have venomous bites!

Lophophorates:

Phylum brachipoda

• Sessile & Coelomate

• Protected between two hinged valves (Top & Bottom Shells)

• Are NOT related to bivalve molluscs!

Lophophore and pedicle present

Brachiopoda are

very abundant in fossil record (Paleozoic) now only about 350 species remain

LOST spiral cleavage

• Shells of Calcite (CaCO₃) & proteins

• Usually dioecious

• Incomplete or complete U-shaped digestive tract

Phylum Brachiopoda
Class Inarticulata

• Primitive

• Simple hinge mechanism & no teeth on valves

  • Simply use muscles to open and close shell

• Includes Lingula - oldest known animal genus still extant!

• Pedicle anchors in soft sediment

• Bristles around shell edges known as setae

• Valves (Shells) are soft and flexible

Phylum Brachiopoda
Class Articulata

• Include the “Lamp shells” 

  • Many look like ancient oil lamps

• Articulated valves

  • Many have “teeth”   to lock the shells closed

• Complex  hinge

• Pedicle anchors on rocks

• No setae

• Very few remain alive today

Branchipods vs Bivalve

• Top and bottom shells are NOT mirror-images of each other

• Pedicle anchors them in place (pedicle hole visible even in fossil brachiopods)

• Filter-feed using a lophophore

Branchipods vs Bivalve

• Left and right shells are mirror-images (mostly) of each other

• Muscular foot allows them to move (at least a little bit)

• Filter-feed using 4 oversize gills