Protostome The Deuterostomes Deuterostomes Echinoderms and Chordates The SECOND opening of Ch 35 the digestive system (in the gastrula stage) becomes the mouth Deuterostomes Characteristics: • Bilaterally symetrical • Coelomate • Blastopore fate (anus) – Second opening in the gastrula becomes the mouth – This developmental similarity between echinoderms and chordates is supported by DNA sequence data Phylum Echinodermata Why are Echinoderms considered (Gk: echin = spiny; derma = skin) to be bilaterally symmetrical? • 5 Classes: Sea stars, brittle stars, sea urchins, sand dollars, sea cucumbers • A thin skin covers an endoskeleton of hard calcareous plates • 7,500 species – all marine 1 Adults - Pentaradial Echinoderm larvae are bilateral Starfish larvae Sea Urchin larva Sea Cucumber Some species are commercially harvested for human food Echinoderm Features • Unique “water vascular system” • A network of hydraulic canals used in: • locomotion • feeding • gas exchange • excretion 2 Sea Star anatomy Tube feet of a sea cucumber • Muscle and nervous tissue, but no cephalization Sea Star feeding on a bivalve in adults • Endoskeleton of hard calcareous plates • Complete (but short) digestive system • No specialized respiratory, circulatory, or excretory systems • Separate male and female individuals • External fertilization Everts stomach into the bivalve to digest it INSIDE ITS OWN SHELL!! Sea stars = Keystone predators Crown-of-thorns sea star • Keystone species - plays a unique role in the • Feed on the living cnidarians that produce coral reefs way ecosystems function – greater than • Population explosions of the crown-of-thorns sea star what their biomass would suggest. can severely damage coral reefs • Sea stars eat shell fish (urchins, mussels, • Causes of outbreaks appear to be removal of natural etc) that most others do not eat predators and increased nutrient levels in the water • If sea urchins and/or mussels (herbivores) (both due to human activities) take over what will happen? • Control efforts include injection of ! individual starfish with chemical toxins 3 Phylum Chordata Phylum Chordata • Divided into 3 subphyla, which include 11 This phylum includes the animals that major groups of chordates are most familiar to us - and includes humans. • Some of the 11 groups are defined as “Classes” by biologists • Others of the 11 groups are currently considered to be “clades”, i.e. formal taxonomic level has not been agreed upon Chordates! Fig 35.12 • Chordate does NOT = Vertebrate All chordates have four characteristics 1. Pharyngeal slits (at some developmental stage) • Openings to the outside of the body at the pharynx (region just behind the mouth) 1. Pharyngeal gill slits – Allows water that enters the mouth to exit without passing though the gut in invertebrate chordates 2. Dorsal hollow nerve cord – Modified for gas exchange or other functions in vertebrates 3. Notochord 4. Post-anal tail Fig. 34.3 Pharyngeal slits 4 2. Dorsal hollow nerve cord 2. Dorsal hollow nerve cord • Unique to chordates • Nerve cord develops into the central nervous – Other animals have a solid nerve cord that is usually system ventrally located – Brain and spinal cord Dorsal hollow nerve cord Ventral solid 3. Notochord 4. Muscular post-anal tail • A flexible rod located between nerve cord and gut • Skeletal elements (notochord) and muscles – Provides skeletal support for muscle attachment • Lost during embryonic development in many – Only remnants of embryonic notochord found in most species adult vertebrates – Non-chordates have a digestive tract that extends the length of the body Notochord Post-anal tail Phylum Chordata Subphylum Cephalochordata Three Subphyla: • Called “lancelets” because of their blade-like shape 1. Cephalochordata • Chordate characteristics persist into adulthood • Globally rare, but some places have high 2. Urochordata population density (e.g., Tampa Bay, Florida) 3. Vertebrates 5 Lancelet Anatomy Suspension feeders that use their pharyngeal slits to filter out small food particles Typically present buried tail-first in sand Subphylum Urochordata Adult tunicates don’t look much like a “chordate” • Tunicates (“sea squirts”) • No notochord, nerve cord or tail • Filter feeders with incurrent and excurrent siphons Adult tunicates don’t look much Some tunicate species are like a “chordate” colonial • But these features are present in the tunicate larval form… 6 The Vertebrates! Subphylum Vertebrates • Chordates with a skull (either bone or cartilage) • Includes all of the animals we call “vertebrates” Finally - something we’ve heard of!! All vertebrates have the same • Includes some large and rather obvious characteristics as chordates animals that are quite familiar to us (at some developmental stage), plus • But remember that vertebrates represent • Pronounced cephalization less than 5% of the known animal species – With a skull (cranium) on Earth • Vertebral column that encloses the nerve cord – Replaces the notochord function • Endoskeletons that grows with the animal • Closed circulatory system • Lampreys 7 Hagfish (Clade Myxini) Jawless Lost vertebrae through evolution (ancestors had vertebrae) 8 .