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Phylum Echinodermata Facts and Information

[Kingdom: Animalia] [Superphylum: Deuterostomia] [Clade: Ambulacraria] [Phylum: Echinodermata]

By far, the vast majority of ancient echinoids are now extinct. But, the five major living classes account for around seven thousand extant (surviving) examples.

This section contains fun facts and interesting information about the echinoderm marine invertebrate animals that belong to the phylum Echinodermata.

Facts about Echinoderms (for Scuba Divers)

In the Greek language, echinoderm means spiny (from "echinos") and skin (from "derma").

The five surviving classes are morphologically diverse, represented by:

Asteroidea (sea stars (starfishes))
Crinoidea (feather stars, sea lilies)
Echinoidea (sand dollars, sea urchins)
Holothuroidea (sea cucumbers)
Ophiuroidea (basket stars, brittle stars, serpent stars)

There are around 13,000 extinct echinoderm species. Hence, understanding how the classifications relate to each other is mostly done through the largest fossilised echinoids and crinoids, some of which are more than 20 metres long (66 feet).

Most of the living classes are found in abundance in all saltwater environments around the world. Plus, almost two hundred species of echinoderms can also survive life in the harshest Arctic regions, mostly brittle stars of the class Ophiuroidea.

But wait - there's more:

The widest distributions occur in the diverse habitats of coral reef formations and shorelines in the tropical waters of the Indian and Pacific Oceans.

By and large, most of the phylum echinodermata have limited depth ranges. Thus, shallower than 100 metres (330 feet) is the norm. Nevertheless, some of the deep-sea specimens can exist at incredible depths - approaching five thousand metres (16,400 feet).

Fun Fact: Only a few species can survive abyssal depths beyond nine kilometres (5 miles). They include 'sea pigs' (Elpidiidae) and some species of sea cucumbers of the genus Myriotrochus.

Characteristics of Echinoderm

The adult stage in deuterostomal (bilaterian) animals is the time when they feature their unmistakable pentaradial five-part symmetry (meaning divisible into five equal parts).

All echinoderms have an internal skeleton made from stereom (calcium carbonate), including the extinct fossilised forms.

Even though these marine invertebrate species display various forms of sensory perception, they lack a "definitive" or well-developed sensory head region.

Here's the thing:

Most echinoderm clades function through a simplified "one-way" digestive system. Even so, they have a diversified range of feeding mechanisms.

Some species are carnivorous, using a mouth, a stomach, and an intestine to metabolise their food, such as small mollusks.

Whereas, others are herbivores and some are detritivores, grazing and chewing on marine algae or getting enough nutrients from dead and decaying organic matter.

Phylum Echinodermata Regeneration Process

It's fair to say that having the ability to regenerate a lost body part is rare in the animal kingdom. Yet, brittle stars and sea stars are able to regrow arms and even divide in half to produce two completely new individuals.

Interesting Fact: Some sea urchins can replace their spines and any lost (or damaged) tube feet. Plus, some sea cucumber species can regrow the whole of their digestive tract.

Echinoderm Size and Colour

Compared to some marine annelids and most saltwater crustaceans, echinoderms are small - rarely growing more than ten (10) centimetres long or diameter (4 inches).

Even so, the snake sea cucumber (Synapta maculata) grows up to three metres long (ten feet), and sunflower sea stars (Pycnopodia helianthoides) have an arm span up to one (1) metre (3.3 feet).

Moving on...

One of the striking features of the echinoderm species is the brilliant colouring. For example, many are flamboyant red, some are radiant orange, and others are green or purple.

In general, the tropical species tend to have dark brown or black body colouring. But, the deep water species that get very little daily sunlight are lighter shades of yellow and white.

How Do Echinoderms Reproduce?

Most of the species have separate sexes (males and females) and, for the most part, reproduction is sexual. Thus, male sperm cells fertilise female eggs. But, some brittle stars, sea cucumbers, and starfishes can also reproduce asexually.

Asexual Reproduction

Some echinoderms display fragmentation, meaning they can divide their body into two (or more) parts. The same procedure is how some species regenerate missing body parts.

Sometimes, "sexual reproduction" fails to occur at all. But, the majority of asteroids, holothurians, and ophiuroids use fragmentation as the normal process for reproducing.

Sexual Reproduction

Generally speaking, echinoderm spawning is an annual occurrence that usually lasts four to eight (8) weeks. Even though some species spawn several times per year, the optimum months are spring and summer when the water gets warmer.

Female echinoderms that reproduce "sexually" cast several million eggs into the water column. At the same time, the males will shed their spermatozoa (a process called spawning) to fertilise the eggs.

Threat and Predators

The major predators of echinoids are crabs, moray eels, octopuses, sharks, and some sea birds. Despite that, they have various defencive mechanisms that include sharp spines, venomous toxins, and the ability to discharge sticky entangling threads.

Important: The IUCN Red List of Threatened Species is a comprehensive source of information about the global conservation status of animals, fungi, and plants. Currently, the IUCN lists the pineapple sea cucumber (Thelenota ananas) as being "Endangered" (EN) and decreasing in population and the European edible sea urchin (Echinus esculentus) as "Near Threatened" (NT).

Echinoderm Species List

Brittle Stars

Feather Stars

Sand Dollars

Sea Cucumbers

Scientists believe tropical sea cucumbers are helping with the global battle against harmful climate change and may reduce the damage that it causes to coral reefs.

This segment contains fun and interesting facts about sea cucumber species, such as where they live, what they eat, and how these holothurian marine invertebrates reproduce.