挑食！以死亡魷魚的喙為食的海螺(原創 克爾-紐曼黑洞)

1888年，摩納哥王儲阿爾貝于亞速爾群島外海約780英尋（約相當于1427米）深度拖網獲得一塊頭足類喙的殘骸。殘骸上棲息著許多微型笠螺，多個個體啃咬出與貝殼基部大小相當的凹坑，有時坑底僅存一層透明薄膜。12年后，Dautzenberg與Fischer根據這些標本建立淵喙螺科Bathysciadiidae。

淵喙螺科是種粒螺目Cocculinida僅有的3個科之一。全科共4屬9種，大多棲息于數千米深的海底，加之其以死亡魷魚喙為食的習性，因此十分罕見。盡管曾有在一個大王烏賊喙上發現百余個淵喙螺Bathysciadium costulatum個體的記錄，但據2023年的一篇論文統計，全世界記錄在案的博物館館藏僅有35批。稀少的發現令淵喙螺的相關研究極少。

淵喙螺擁有標志性的具放射狀流蘇的殼皮，和蟶螂一樣殼皮長于殼體，其作用也和蟶螂的相似——當動物抬高身體以便水流過貝殼與其基座之間時，這些流蘇覆蓋兩側，使得沉積物無法進入貝殼與基座之間。淵喙螺的足部會形成類似吸盤的結構，也是唯一完全缺失中腸腺的非寄生腹足類。淵喙螺殼體脆弱，以至于在干燥環境中，Bathysciadium costulatum的外殼會因殼皮收縮而碎裂。在Bathysciadium costulatum的胃中曾發現刮削下的頭足類喙碎片，推測其依靠共生菌消化這些碎片。

Bathysciadium xylophagum是唯一被發現于木材上的淵喙螺，其棲息于船蛆的蛀洞中。這被認為是在首選基質不存在時的無奈選擇。在葡萄牙西南部外海約瑟芬海山發現的Bathysciadiumcf.xylophagum則棲息于頭足類喙上。除Bathysciadium xylophagum外，僅有2個來自科隆群島（加拉帕戈斯群島）的未命名Xenodonta屬物種確認不以頭足類的喙為食——它們附著在一個尖帽螺科Capulidae個體的殼上并吞噬了它的大部分殼皮。

Bathysciadium xylophagum/ 作者拍攝自有標本

Bathysciadium xylophagum（圖中a、b）

Bathysciadiumcf.xylophagum（圖中c、d）

Xenodonta bogasoni

Bathysciadium pacificum生活的深度范圍極廣，在5500米、4000米至2000米水深都有發現，甚至曾在一條捕獲自549~594米水深處的太平洋油鰈Microstomus pacificus的消化道內發現過一個標本。太平洋油鰈棲息深度為10~1370米。考慮其在冬季才向深水產卵洄游，而含B. pacificum的標本于6月采集到，因此B. pacificum可能在500~800米也有分布。令人遺憾的是這枚標本已經遺失。

Bathysciadium pacificum/ Geiger et al, 2023

淵喙螺科的Pilus conicus

淵喙螺在生命早期就會失去胎殼，齒舌退化，齒數遠少于正常的扇舌型古腹足類齒舌。魷喙螺科Teuthirostriidae的Teuthirostria cancellata盡管同樣棲息于頭足類喙上，卻擁有正常的種粒螺型齒舌。因此魷喙螺科可能代表著種粒螺科Cocculinidae與淵喙螺科之間的過渡——一些種粒螺首先改變食性，以頭足類喙為食，隨后齒舌和消化道因此而退化。魷喙螺科共2屬3種，除T. cancellata外，其余2種均棲息于沉木上。

魷喙螺科的Fedikovella beanii

魷喙螺科的Fedikovella caymanensis

參考文獻及圖片來源

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