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Biology 456 – Zoo Lab 6 Study Notes: Deuterostomia – Phyla Echinodermata, Hemichordata, Study notes of Biology

Rasmussen College - FloridaBiology

Biology 456 – Zoo Lab 6 Revised Study Notes: Deuterostomia – Phyla Echinodermata, Hemichordata, and Basal Chordates: This document provides revised study notes for Biology 456 Zoo Lab 6, focusing on Deuterostomia and the major phyla Echinodermata, Hemichordata, and basal chordates. It covers key zoological concepts including deuterostome embryonic development, anatomical characteristics, evolutionary relationships, body symmetry, locomotion, feeding mechanisms, and distinguishing features of each phylum. The material is designed to support structured revision and strengthen understanding of comparative anatomy, evolution, and animal diversity in zoology coursework.

Typology: Study notes

2025/2026

Available from 06/18/2026

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BIOLOGY 456 ZOO LAB 6 REVISED STUDY NOTES FOR
DEUTEROSTOMIA - PHYLA ECHINODERMATA,
HEMICHORDATA, AND BASAL CHORDATES
Part 1: Deuterostomes
Protostomous Animals
- Ex: lophotochozoa & ecdysozoa
- Mouth derived from blastopore of embryo during development.
- Spiral determinate cleavage
Clade Deuterostomia
- Clades include Echinodermata, hemichordate, and chordata.
- Mouth arises later in development.
- Anus derived from blastopore.
- Possess radial indeterminate cleavage.
Part 2: Phylum Echinodermata
I. General characteristics
- Greek for (echinos = spiny sea urchin) + (derma = skin)
- Spiny skinned marine organisms
- Ex sea stars and sea urchins
- Many are near sessile
- Ancestors of modern echinoderms were totally sessile
- Because of sessility, group has secondarily evolved radial symmetry
- Most have pentaradial symmetry (5 axes of symm.)
- Share a bilateral ancestor with deuterostomes reflected by ontogeny
- Bilaterally symmetrical larval from
- Larval form undergoes a drastic rearrangement which develops into a pentaradial adult
- Sea stars larva = bilaterally symmetrical swimming larva = bipinnaria
- Bipinnaria develops into brachiolaria larva which settles and develops into adult form
II. 5 classes
- Class ophiurodidea
o Brittle stars
o Tube feet with no suckers located on arms
o Mostly suspension feeders
- Class echinoidea
o Sea urchins and irregular urchins
o Includes sand dollars and sand biscuits
o Most feed by scraping algae or bacteria from substrates
o Others feed on tiny particles moved to mouth by tube feet
o Ossicles fuse to form internal test
- Class Crinoidea
o Near sessile suspension feeders
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Download Biology 456 – Zoo Lab 6 Study Notes: Deuterostomia – Phyla Echinodermata, Hemichordata and more Study notes Biology in PDF only on Docsity!

BIOLOGY 456 ZOO LAB 6 REVISED STUDY NOTES FOR

DEUTEROSTOMIA - PHYLA ECHINODERMATA,

HEMICHORDATA, AND BASAL CHORDATES

Part 1: Deuterostomes Protostomous Animals

  • Ex: lophotochozoa & ecdysozoa
  • Mouth derived from blastopore of embryo during development.
  • Spiral determinate cleavage Clade Deuterostomia
  • Clades include Echinodermata, hemichordate, and chordata.
  • Mouth arises later in development.
  • Anus derived from blastopore.
  • Possess radial indeterminate cleavage. Part 2: Phylum Echinodermata I. General characteristics
  • Greek for (echinos = spiny sea urchin) + (derma = skin)
  • Spiny skinned marine organisms
  • Ex sea stars and sea urchins
  • Many are near sessile
  • Ancestors of modern echinoderms were totally sessile
  • Because of sessility, group has secondarily evolved radial symmetry
  • Most have pentaradial symmetry (5 axes of symm.)
  • Share a bilateral ancestor with deuterostomes reflected by ontogeny
  • Bilaterally symmetrical larval from
  • Larval form undergoes a drastic rearrangement which develops into a pentaradial adult
  • Sea stars larva = bilaterally symmetrical swimming larva = bipinnaria
  • Bipinnaria develops into brachiolaria larva which settles and develops into adult form II. 5 classes
  • Class ophiurodidea o Brittle stars o Tube feet with no suckers located on arms o Mostly suspension feeders
  • Class echinoidea o Sea urchins and irregular urchins o Includes sand dollars and sand biscuits o Most feed by scraping algae or bacteria from substrates o Others feed on tiny particles moved to mouth by tube feet o Ossicles fuse to form internal test
  • Class Crinoidea o Near sessile suspension feeders

o Feathery arms used to collect tiny particles from surrounding water o Often attach to suberate by a long stalk

  • Class Holothuroidea o Sea cucumbers = bilateral, no arms o Motile o Body elongated along oral-aboral axis o Tube feet on ventral surface around mouth II. Diversity Class Ophiuroidea
  • Different than Asteroidea (sea stars) due to: ARMS o Brittle stars have narrowly joined arms to central disk of body o No visceral organs o Arms contain small extension of coelom o Rest of arm is muscle and ossicles o Autonomy and regeneration occur easily o Arms posses tube feet o Arms not restricted to ambulacral groove o Tine feet occur on all surfaces of arm o Manu use tube feet for suspension feeding o Arms important in locomotion o Sinusoidal movement of arms used to move along ocean floor
  • SIMILAR TO Sea stars oral surface is oriented downward with mouth in the center of the oral disk
  • HOWEVER Madreporite not on aboral surface as in sea stars but on ORAL SURFACE near the mouth
  • Anus lost in brittle stars = solid wate removed via mouth
  • Oral surface of central disk near base of each arm are slits = opening to Genitorespiratory bursae
  • Genitorespiratory bursae pouches arranged around the central disk between each of the arms containing gonads used for reproduction and gas exchange CLASS ECHINOIDEA
  • includes sea urchins and irregular urchins (sand dollars and sea biscuits)
  • posses a test (internal shell made of fused ossicles)
  • sand dollar common in American beach combers is the test of an irregular urchin
  • test of ancient irregular urchins = common fossil find
  • test of sea urchins results in rigid body
  • body of sea urchins no arms but still pentaradial symmetrical
  • moveable spines near body of sea urchins (can be long or short) = extensions of ossicles
  • spines used for protection and locomotion
  • possess multiple types of pedicellariae and tube feet all over body
  • most well know echinoderms
  • includes sea stars aka starfish aka sun stars
  • pentaradial symmetry
  • arms in multiples of fice
  • not uncommon for 6 arms
  • condition often a consequence of regeneration
  • arms joined to central oral disk
  • aboral surface faces up
  • oral surface oriented towards substrate
  • aboral surface covered w tiny fixed non moveable spines
  • fixed spines under dissecting scope appear as small off white bumbs on orange surface of body
  • bumps are extension of dermal ossicles
  • at higher magn. Ring of tiny pedicellaria visible around base of each fixed spine
  • dermal brachia (populae) scatter over surface of body
  • populaae appear as tiny finger like projections either alone or in groups
  • distal end of each arm is a tiny eyespot used for light detection o tip of the arm is a group of tiny moveable spines w no pedicellariae o spines are arranged ina. Ring surrounding eyespot
  • on oral disk o small circular structure visible near vertex of angle between two arms= madreporite o madreporite serves as entrance to water vascular system o on injected specimen this structure may be pink as a result of extrusion of latex during injection process o allows water to enter white preventing entrance of solid particles
  • on oral surface of body o well developed ambulacral groove w numerous tube feet o tube feet have sucked used for locomotion and move food to mouth o ambulacral groove runs down middle of each arm from distal tip to mouth o tube feet extend from center or ambulacral groove o on lateral margins of each ambulacra groove is a line of larger moveable spine o moveable spine used with tube feet for locomotion

Phylum Hemichordata

Overview

  • Hemichordates belong to the deuterostomes , a group that also includes: o Echinodermata o Chordata
  • The name Hemichordata means “half-chord” (Greek: hemi = half, chorda = cord).
  • They were originally thought to share the notochord characteristic of chordates.

New Understanding

  • Molecular evidence shows hemichordates are more closely related to echinoderms.
  • Their support structure, the stomochord , was once thought to be a notochord but is not homologous to the chordate notochord.

Larval Similarities

  • Hemichordates share developmental similarities with echinoderms.
  • Their tornaria larva is very similar to the bipinnaria larva of echinoderms.

Hemichordate Body Plan

Most hemichordates are worm-like marine animals. Two main classes:

1. Pterobranchia

Characteristics:

  • Sessile (attached to a surface)
  • Often colonial
  • Build tube-like structures similar to tube worms
  • Have complex tentacles Feeding:
  • Suspension feeders
  • Use tentacles to capture food particles from the water.

2. Enteropneusta (Acorn Worms)

Characteristics:

  • Commonly called acorn worms
  • Burrowing animals
  • Deposit feeders (consume sediment to obtain organic matter)
  • Filter feeding
  • In some organisms, gas exchange

4. Metameric Segmentation

  • Body is divided into repeating segments
  • Also found in: o Arthropods o Annelids Important:
  • Segmentation likely evolved independently in these groups.

5. Post-Anal Tail

  • Tail that extends beyond the anus
  • Often used for locomotion

6. Endostyle

  • Located in the ventral portion of the pharynx
  • Ciliated structure
  • Produces mucus for food capture Important evolutionary note:
  • In vertebrates, the thyroid gland develops from the endostyle.

Ascidians (Tunicates) Larval Stage

Ascidian Tadpole

  • A microscopic swimming larva
  • Does not feed
  • Has structures similar to adults: o Pharynx o Siphons

Siphons

Two types:

  1. Incurrent siphon o Located near the anterior end o Water enters here
  2. Excurrent siphon o Located mid-dorsally o Water exits here

Other Features

  • Pharyngeal slits visible under microscope
  • Post-anal tail present

Metamorphosis

Before becoming an adult:

  1. Larva attaches to a substrate using adhesive papillae
  2. During metamorphosis: o Siphons move posteriorly o Tail disappears o Notochord disappears o Nerve cord disappears Adult tunicates lose most chordate traits.

Subphylum Craniata

Craniata includes animals formerly called vertebrates. Key idea:

  • Some animals (like hagfish ) have no vertebrae but do have a skull. Thus the name Craniata (organisms with a cranium).

Phylum Chordata Classification

Three subphyla:

1. Cephalochordata

Example:

  • Lancelets (amphioxus) Characteristics:
  • Burrowing deposit feeders
  • Retain all chordate characteristics as adults

2. Urochordata

Example:

  • Sea squirts (tunicates) Characteristics:
  • Sessile suspension feeders
  • Adults lose most chordate characteristics
  • Covered by cellulose tunic

3. Craniata

  • Includes vertebrates
  • Possess a cartilaginous or bony cranium Function:
  • Supports and protects the brain/skull

Subphylum Cephalochordata (Lancelets)

General Characteristics

  • Small animals ( few centimeters long )
  • Elongated body
  • Tapered posterior end Behavior:
  • Burrow in sediment at an angle
  • Ventral side faces upward
  • Mouth remains exposed

Feeding Mechanism

  1. Tentacles around mouth o Sort food particles
  2. Water flow: o Water enters the mouth o Moves across the pharynx
  3. Pharyngeal slits o Collect food particles
  4. Water enters the atrium
  5. Water exits through the atriopore

Food Processing

  • Food gets trapped in mucus produced by the endostyle
  • Moved posteriorly to the hepatic cecum
  • Then enters the intestine
  • Waste exits through the anus Important:
  • Anus is posterior to the atriopore

Internal Structures

  1. Water enters incurrent siphon
  2. Passes through pharynx
  3. Moves across pharyngeal slits
  4. Enters atrium
  5. Leaves via excurrent siphon Food capture:
  • Endostyle secretes mucus
  • Food particles stick to mucus
  • Cilia move food to esophagus