ECHINODERMATA Guia

Approx. 7,000 species.
Term derived from Greek words "echinos" (spine) and "dermis" (skin) indicating their spiny skin.
Primarily marine benthic organisms.

Complete digestive system.
Extensive coelomic cavity.
Hemal system supported by the coelom and the water vascular system (WVS):
- Glandula axial
- Rings: Oral, Gastric, Aboral.
- Sinuses: Radial, Gastric, and Genital.
- Aboral sac.
Respiration through body wall via WVS, utilizing:
- Papulae in Asteroidea.
- Podia (tube feet).
- Gills in Echinoidea.
- Branchial trees in Holothuroidea.
Lack of excretory system.
Dioecious with simple gonads, usually releasing dipleura larvae.
- Some hermaphroditic species exist and have external fertilization (some with incubation chambers).
- Gonopores located aborally at interambulacral positions.
Nervous system structured as:
- Nervous ring and radial nerves:
  - Hyponeural, Ectoneural, Endoneural, and Lateral from podia.
Ambulacral system utilized for locomotion, feeding, and gas exchange:
- Tiedmann's bodies assist in clearing obstructions within the water vascular circuit.

Highly diverse group constituting 90% of deep-sea benthos.
Bioturbators influencing sedimentary processes.
Control populations, serve as prey for other organisms, and are vital to coral reef ecosystems.
Economically significant, consumed worldwide, and used in ornamental trades.

Sessile, divided into:
- Sea lilies: Have stalks (peduncle).
- Feather stars: Possess cirri.
Five ambulate plates regardless of the number of arms.
Doliolaria larva evolves into pentacrinoid larva.
Animals demonstrate pentaradial symmetry.
- Body consists of a cup-like calyx; mouth may be on the lateral margin or central.
- Five arms extend from the calyx, commonly branched and subdivided.
- Pinnulated arms for defense, feeding, and reproduction.
Approximately 80 stalked species live below 200m; 540 un-stalked species (Comatulida) inhabit shallower waters.
Movement is slow, often attached to substrates like corals or rocky outcrops.
Filter feeders consuming zooplankton (foraminifera, small crustaceans) and phytoplankton.
Dioecious with external fertilization.
Larval development shows bilateral to pentaradial symmetry; stalk is lost in Comatulida adults.
Crinoids can autotomize arms for self-defense and regenerate limbs rapidly.

Star-shaped body with radial symmetry.
Each arm contains all vital systems enabling fragmentation-based reproduction.
Reproductive modes include:
- Asexual through fragmentation vs. sexual methods: bipinnaria and brachiolaria larvae.
Classified into 7 orders:
- Forcipulatida, Brisingida, Notomyotida, Spinulosida, Paxillosida, Valvatida, Velatida.
Calcified skeleton formed by flat plates connected by collagen and internal ossicles.
Some species possess venomous spines; variable surfaces (smooth, granular, spiny) with vivid colors and patterns.
Earliest records date back to the Ordovician period but are incomplete due to disintegration of soft tissues.
Mouth located on the oral surface, with the anus aborally positioned.
- Many asteroids utilize external digestion by eviscerating stomachs over prey—capable of consuming larger organisms.
- Feeding primarily on bivalves, gastropods, arthropods, and small fish.
Slow movement via hydraulic-operated tube feet.
Complex life cycles, capable of both sexual and asexual reproduction.
- Many species are dioecious; some hermaphroditic with larval stages exhibiting bilateral symmetry.
- Regeneration abilities present, but complete disc regeneration varies by species.

Star-shaped body showing radial symmetry.
Each arm contains 4 muscular bundles connected by ossicles; have maxillary plates around the mouth for expelling non-digested material.
Gonads located on the central disc.
Ability to regenerate arms; some can split at the disc level.
Primarily dioecious, with simultaneous hermaphroditism or protandry noted.
Display only horizontal movement.

Divided into:
- Regulars (globular) and irregulars (bilateral symmetry).
Possess the Aristotle's lantern, a calcified structure not growing proportionately with the organism.
Digestive anatomy:
- Intestine encircles the urchin, with the siphon for food circulation.
Respire via gills and tube feet.
Senses of balance via statocysts located in ambulacral regions; exhibit negative phototaxis based on light levels.
Reproductive behavior involves producing numerous gametes, indicating high reproductive capacity.
- Regenerative capabilities exist, though threatened by predation.
- Common habitats found in rocky or sandy substrate.

Reacts defensively when disturbed, releasing gametes and defensive tubes.
External morphology includes:
- Trivial: contact with substrate.
- Bivial: not in substrate contact.
Internal structure:
- Skeletal pieces bound by connective tissue, lacking plates.
- Possess an internal madreporite allowing water intake through the anus.
- Contains branchial trees with alcubier tubes.

Upon disturbance, organisms eject Cuvierian tubules, followed by respiratory trees, and in extreme cases, expel other organs. Some species exhibit body autonomy.
Produce holothurins, a group of toxins derived from sea cucumbers aiding in defense.

Genes associated with notochord and pharyngeal slits are inactivated but present.
High-quality DNA supporting rapid regeneration.
Regulatory systems for regeneration might provide insights into cancer control.

Many species exhibit hermaphroditism and reproduce via budding.
Order Apodida: Worm- or snake-like body lacking tube feet and respiratory trees, digitated tentacles, calcified ring without extensions.
Order Dendrochirotida: Extensive branched tentacles, present respiratory trees; retractable muscles.
Order Elasipodida: Tentacles functioning as plates or shields for digging, may or may not possess respiratory trees; soft, gelatinous body walls with elongated papillae.
Order Molpapiida: Distinctive thick body tapering into a tail.
Order Persiculida: Globe-shaped with ambulacral regions.
Order Holothuriida: General characteristics based on cucumber morphology, including deep-sea cucumbers (Order Synallactida) which might lack respiratory trees.

Function as significant bioturbators, aiding substrate turnover and supporting marine biodiversity.