挑食！以死亡魷魚(yú)的喙為食的海螺(原創(chuàng) 克爾-紐曼黑洞)

1888年，摩納哥王儲(chǔ)阿爾貝于亞速爾群島外海約780英尋（約相當(dāng)于1427米）深度拖網(wǎng)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(gè)個(gè)體啃咬出與貝殼基部大小相當(dāng)?shù)陌伎?，有時(shí)坑底僅存一層透明薄膜。12年后，Dautzenberg與Fischer根據(jù)這些標(biāo)本建立淵喙螺科Bathysciadiidae。

淵喙螺科是種粒螺目Cocculinida僅有的3個(gè)科之一。全科共4屬9種，大多棲息于數(shù)千米深的海底，加之其以死亡魷魚(yú)喙為食的習(xí)性，因此十分罕見(jiàn)。盡管曾有在一個(gè)大王烏賊喙上發(fā)現(xiàn)百余個(gè)淵喙螺Bathysciadium costulatum個(gè)體的記錄，但據(jù)2023年的一篇論文統(tǒng)計(jì)，全世界記錄在案的博物館館藏僅有35批。稀少的發(fā)現(xiàn)令淵喙螺的相關(guān)研究極少。

淵喙螺擁有標(biāo)志性的具放射狀流蘇的殼皮，和蟶螂一樣殼皮長(zhǎng)于殼體，其作用也和蟶螂的相似——當(dāng)動(dòng)物抬高身體以便水流過(guò)貝殼與其基座之間時(shí)，這些流蘇覆蓋兩側(cè)，使得沉積物無(wú)法進(jìn)入貝殼與基座之間。淵喙螺的足部會(huì)形成類似吸盤(pán)的結(jié)構(gòu)，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(huán)境中，Bathysciadium costulatum的外殼會(huì)因殼皮收縮而碎裂。在Bathysciadium costulatum的胃中曾發(fā)現(xiàn)刮削下的頭足類喙碎片，推測(cè)其依靠共生菌消化這些碎片。

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

Bathysciadium xylophagum/ 作者拍攝自有標(biāo)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(fā)現(xiàn)，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(nèi)發(fā)現(xiàn)過(guò)一個(gè)標(biāo)本。太平洋油鰈棲息深度為10~1370米?？紤]其在冬季才向深水產(chǎn)卵洄游，而含B. pacificum的標(biāo)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(biāo)本已經(jīng)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(huì)失去胎殼，齒舌退化，齒數(shù)遠(yuǎn)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(guò)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(xiàn)及圖片來(lái)源

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Dall W H, 1927. Small shells from dredgings off the southeast coast of the United States by the United States Fisheries Steamer "Albatross", in 1885 and 1886[J]. Proceedings of the United States National Museum, 70(2667): 1-134.

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