| Abstract from DBPedia | An echinoderm (/ɪˈkaɪnəˌdɜːrm, ˈɛkə-/) is any member of the phylum Echinodermata (/ɪˌkaɪnoʊˈdɜːrmətə/). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or "stone lilies". Adult echinoderms are found on the sea bed at every ocean depth, from the intertidal zone to the abyssal zone. The phylum contains about 7,000 living species, making it the second-largest grouping of deuterostomes, after the chordates. Echinoderms are the largest entirely marine phylum. The first definitive echinoderms appeared near the start of the Cambrian. The echinoderms are important both ecologically and geologically. Ecologically, there are few other groupings so abundant in the biotic desert of the deep sea, as well as shallower oceans. Most echinoderms are able to reproduce asexually and regenerate tissue, organs, and limbs; in some cases, they can undergo complete regeneration from a single limb. Geologically, the value of echinoderms is in their ossified skeletons, which are major contributors to many limestone formations, and can provide valuable clues as to the geological environment. They were the most used species in regenerative research in the 19th and 20th centuries. Further, some scientists hold that the radiation of echinoderms was responsible for the Mesozoic Marine Revolution.棘皮動物（きょくひどうぶつ）とは、棘皮動物門（学名: phylum Echinodermata）に属する動物の総称である。ウニ、ヒトデ、クモヒトデ、ナマコ、ウミユリなどが棘皮動物に属する。 とで構成される。 棘皮動物という名称は、echinoderm というギリシア語由来のラテン語を直訳したもので、echinoderm とは echinos（ハリネズミ）のような derma（皮）を持つものという意味である。その名が示す通り、元来ウニを対象としてつけられた名称であるが、ヒトデ、ナマコ、ウミユリなど、棘をもたないがウニと類縁関係にある動物も棘皮動物に含まれる。成体は五放射相称、三胚葉性、海にのみ生息し、自由生活。僅かな種をのぞき底生性。雌雄異体が多い。消化管は口から肛門につながるが、一部の種では肛門が退化している。 (Source: http://dbpedia.org/resource/Echinoderm) |
