Echinoderms and Hemichordates

Echinodermata

• "Echinodermata" means "prickly skin" (due to external spines or projections)

• Calcareous endoskeleton: plates or scattered ossicles

• Evolved from bilateral ancestors (larvae show bilateral symmetry)

• Adults have pentaradial symmetry with ambulacral (radial) grooves

• Unique water vascular system for movement and feeding

• No brain

• Usually a complete digestive system

• Cannot osmoregulate → avoid brackish water

• Mostly benthic (bottom-dwelling) species

• No known parasitic echinoderms (few are commensal)

• Feeding varies: some are particle feeders, others predators

Features found only In Echinoderm

include pentaradial symmetry, a water vascular system, and calcareous endoskeletons unique to this phylum.

Echinodermata Symmetry

free-living larval stages exhibit bilateral symmetry

Pedicellariae

• small pincer-like structures that help to keep the body surface clean and defend against predators.

Dermal Branchiae

• projections of the coelomic cavity covered with epidermis and lined with peritoneum

• Ciliary action moves fluids in the opposite direction (countercurrent)

Class Asteroidea

A class of echinoderms, commonly known as sea stars, characterized by their star-shaped body and ability to regenerate lost arms.

• mouth underside

Water- Vascular system

A unique hydraulic system found in echinoderms, responsible for locomotion, feeding, and gas exchange through the use of tube feet.

Madreporite

A perforated structure in echinoderms that regulates water entry into the water vascular system, aiding in locomotion and feeding.

Stone Canel

Reinforced canal connecting madreporite to ring canel

Polian Vesicles

storage fluid structures- regulate internal pressure

Radial Canal

Symmetrically from ring canal and run the length of arm toward the tips of the arms.

Tube foot extension

• Circumlongitudinal (CLD) muscles contract and podial longitudinal LD muscles relax

• fluid forced into podial region extending by hydraulic pressure

• End of podium gains traction by suction of duo-adhesive glands

Tube feet Retraction

• Circumlongitudinal (CLD) muscles relax and podial longitudinal (LD) muscles contract, pulling the tube foot back. This process allows the tube foot to retract and gain stability for movement or attachment.

Feeding

Echinoderms typically utilize tube feet and a water vascular system to facilitate feeding. They often exhibit various feeding strategies, including predation and filter feeding.

Reproduction

Sexes seperate

Pairs of gonads

Fertilization is external

occurring in the water, often leading to larval stages that develop into adults.

Hemichordata

A phylum of marine deuterostome animals that includes acorn worms and pterobranchs, characterized by a body divided into three parts: proboscis, collar, and trunk. They share features with both echinoderms (larvae) and chordates (gill slits).

Characteristics Hemichordata

1. Bilaterally symmetrical, soft bodied; triploblastic; free
   living.

2. Digestive system complete

3. Longitudinal and Circular muscles

4. A single glomerulus connected to blood vessels may have
   excretory function (metanephridium)

5. Respiratory system of gill slits connecting the pharynx
   with outside

6. Circulatory system of dorsal and ventral vessels and
   dorsal heart

Enteropneusta

• Wormlike acorn worms

• cilla carry particles to mouth

• Contraction of body musculature forces excess water out through gill slits

Pterobranchia

• Small, colonial hemichordates that live in secreted tubes. - They possess a distinctive body plan with a proboscis and a collar that contains gill structures for feeding and respiration.

• Both dioecious and monoecious

• asexual reproduction