Sea urchin | Wikipedia audio article
Channel: wikipedia tts
Date: 02/10/2019

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Sea_urchin


00:01:51 1 Diversity
00:03:31 2 Description
00:05:03 3 Systems
00:05:12 3.1 Musculoskeletal
00:08:04 3.2 Feeding and digestion
00:11:27 3.3 Circulation and respiration
00:13:17 3.4 Nervous system and senses
00:14:31 4 Life history
00:14:41 4.1 Reproduction
00:15:48 4.2 Development
00:17:08 4.3 Life cycle and development
00:18:29 5 Ecology
00:18:38 5.1 Trophic level
00:19:04 5.2 Predators, parasites, and diseases
00:20:51 5.3 Anti-predator defences
00:21:40 5.4 Range and habitat
00:23:51 6 Evolution
00:24:00 6.1 Fossil history
00:26:20 6.2 Phylogeny
00:26:29 6.2.1 External
00:26:55 6.2.2 Internal
00:27:06 7 Relation to humans
00:27:16 7.1 Injuries
00:28:07 7.2 Science
00:30:33 7.3 As food
00:32:53 7.4 As tools
00:33:11 7.5 Aquaria
00:33:35 7.6 Folklore
00:34:12 8 See also



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SUMMARY
=======
Sea urchins, or simply urchins (), are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to 5,000 metres (16,000 ft; 2,700 fathoms). Their tests (hard shells) are round and spiny, typically from 3 to 10 cm (1 to 4 in) across. Sea urchins move slowly, crawling with their tube feet, and sometimes pushing themselves with their spines. They feed primarily on algae but also eat slow-moving or sessile animals. Their predators include sea otters, starfish, wolf eels, and triggerfish.
Like other echinoderms, urchins have fivefold symmetry as adults, but their pluteus larvae have bilateral (mirror) symmetry, indicating that they belong to the Bilateria, the large group of animal phyla that includes chordates, arthropods, annelids and molluscs. They are widely distributed across all the oceans, all climates from tropical to polar, and inhabit marine benthic (sea bed) habitats from rocky shores to hadal zone depths. Echinoids have a rich fossil record dating back to the Ordovician, some 450 million years ago. Their closest relatives among the echinoderms are the sea cucumbers (Holothuroidea); both are deuterostomes, a clade which includes the chordates.
The animals have been studied since the 19th century as model organisms in developmental biology, as their embryos were easy to observe; this has continued with studies of their genomes because of their unusual fivefold symmetry and relationship to chordates. Species such as the slate pencil urchin are popular in aquariums, where they are useful for controlling algae. Fossil urchins have been used as protective amulets.