Large-bellied nautilus - Large-bellied nautilus

...The arms are not elastic like those of dibranchs, but are short whisker-like tentacles that are contained within a muscular sheath, and there are 60 to 90 of them, with a double set surrounding the mouth. Compared to the approximately 3,500 fossil species, there are only four extant species, the others being the Palau Nautilus N. belauensis found in the Palau Islands, the large-bellied Nautilus N. macromphalus found from New Caledonia to Fiji, and the broad-bellied Nautilus N. scrobiculata found in New Guinea. [Takashi Okutani]
[Fossils and systematics]
The fossil nautiloids (subclass) Nautiloidea consist of approximately 75 families, 300 genera and 3,500 species, with the order Nautilida alone consisting of 24 families and 165 genera. They appeared in the early Paleozoic era and flourished in the geological period to a degree incomparable to the present.

*Some of the terminology explanations that mention the "Giant Nautilus" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…腕は，二鰓類のように伸縮せず，筋肉質のさやの中に収まる短いひげ状の触手で，口の周囲を取り巻いて二重にあり，60～90本ある。化石種は約3500種と多いのに比べ，現生種はわずかに4種で，他にパラオ諸島にパラオオウムガイN.belauensis，ニューカレドニアからフィジーにかけてオオベソオウムガイN.macromphalus，ニューギニアにヒロベソオウムガイN.scrobiculataが産する。【奥谷 喬司】
【化石と系統分類】
　化石オウムガイ類(亜綱)Nautiloideaはほぼ75科300属3500種，オウムガイ目Nautilidaだけでも24科165属あって，古生代初期から出現し，地質時代には現在とは比べるべくもなく繁栄した。…

※「オオベソオウムガイ」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報