Untitled Quiz

Phylum Echinodermata

• Comprises spiny-skinned marine animals with around 7,000 existing species and numerous extinct forms registered in the fossil record.
• Exclusively marine habitat, ranging from intertidal zones to deep-sea environments, primarily benthic.
• Includes notable members like starfishes, brittle stars, sea urchins, sea cucumbers, and sea lilies.

Cleavage Patterns

• Deuterostomes, including echinoderms, exhibit radial cleavage, while most protostomes demonstrate spiral cleavage.

Gastrulation Differences

• In protostomes, the first embryonic opening becomes the mouth, whereas in deuterostomes, it becomes the anus.

Classification of Echinodermata

• Divided into five classes:
  • Crinoidea (sea lilies, feather stars)
  • Ophiuroidea (brittle stars, basket stars)
  • Asteroidea (starfishes or sea stars)
  • Holothuroidea (sea cucumbers)
  • Echinoidea (sea urchins, sand dollars)

Controversial Hypotheses

• There are two main hypotheses regarding echinoderm classification:
  • Asterozoan hypothesis
  • Cryptosyringid hypothesis

Main Characteristics of Echinodermata

• Defined by four unique characteristics known as synapomorphies:
  • Pentamerous radial symmetry evident in adult forms.
  • Calcareous skeleton made of ossicles.
  • Mutable collagenous tissue allowing flexibility.
  • Unique water vascular system for locomotion and feeding.

Pentamerous Radial Symmetry

• Adults display five-part symmetry around a central axis, evolving from a bilateral ancestor; larvae retain bilateral symmetry.

Calcareous Skeleton

• The mesodermal skeleton is composed of calcium carbonate ossicles, which form various structural configurations from flexible to rigid, contributing to the phylum's name due to spiny texture.

Mutable Collagenous Tissue

• Ligaments composed of collagen are neural-controlled, allowing for adjustments in body rigidity for different species, such as flexible bodies in sea cucumbers and rigid forms in sea urchins.

Water Vascular System

• A fluid-filled canal system originally for respiration and food transport; also aids in locomotion via tube feet. No excretory organs or centralized brain; generally dioecious in reproductive structure with external fertilization.

Madreporite

• A calcareous structure that filters water into the water vascular system, indicating the intake point into the system.

Tube Feet

• Muscular extensions of the water vascular system that function in locomotion and attachment; equipped with suckers, extended by hydraulic pressure from the body's muscular sacs (ampullae).

Classes of Echinoderms

• Major groups include:
  • Class Crinoidea
  • Class Asteroidea
  • Class Ophiuroidea
  • Class Echinoidea
  • Class Holothuroidea

Class Crinoidea

• Comprises sea lilies and feather stars, primarily suspension feeders with long arms for catching food.
• Sea lilies are typically sessile in deep water, while feather stars can crawl and swim.
• Ancestral forms likely emerged as stalked sea lilies, with the mouth positioned on the upper surface, representing a basal group.

Class Asteroidea

• Characterized by starfishes with varied adaptations for predation and environmental interaction.