把木頭當(dāng)飯吃，它們是深海木材分解者（下）（克爾-紐曼黑洞）

木材通過河流輸入等因素進(jìn)入大海，并在被海水浸透后沉入深海，成為這片缺乏初級(jí)生產(chǎn)環(huán)境的特殊碳源。這些“有機(jī)島嶼”片段化且存在時(shí)間短暫，因此棲息于此的生物往往演化出長(zhǎng)距離擴(kuò)散策略。許多食木蛤（約35%的物種）殼表都有不挖洞的微型生物個(gè)體固著。研究者曾認(rèn)為這些微型個(gè)體是食木蛤幼體，因此認(rèn)為它們具有育幼習(xí)性。但后來的研究證實(shí)這些微型個(gè)體實(shí)際上是食木蛤的矮雄。矮雄以足絲固定在較大個(gè)體體表，僅有胎殼，營(yíng)濾食生活。一些物種如Xylophaga supplicata的大的挖洞個(gè)體則是先雄后雌的雌雄同體，但其矮雄不能轉(zhuǎn)變?yōu)榇蟮耐诙磦€(gè)體。另一些物種如Xylophaga dorsalis和Xylophaga depalmai則是雌雄異體。一些食木蛤的性別受環(huán)境影響，如雌雄異體的Xylonora atlantica在食物充足的新棲息地，性別比例會(huì)偏向雌性。隨著木材被第一世代持續(xù)消耗，食物與空間資源逐步減少，之后世代的雄性比例逐漸增加，最終導(dǎo)致幼體直接在雌性殼上定居，形成矮雄。

食木蛤的浮游幼體可以長(zhǎng)時(shí)間維持浮游生活，大幅推遲變態(tài)時(shí)間。例如，Xylonora atlantica幼蟲可延遲變態(tài)達(dá)6個(gè)月之久，同時(shí)能進(jìn)入遠(yuǎn)離海底的上層海水。懸浮于海底上方20米水層中的木材仍可被大量食木蛤定殖，因此，一些物種分布范圍極廣，可跨海盆分布。但與此同時(shí)，由于深海沉木獲取困難，所以有大量食木蛤定殖的現(xiàn)象僅被發(fā)現(xiàn)過一次，有些物種甚至出現(xiàn)在遠(yuǎn)離陸地的深淵平原或海溝，這些區(qū)域的木材沉降事件是極其罕見的。

一些食木蛤會(huì)選擇棲居的木材，如Abditoconus brava幾乎僅生活于松木而非橡木中，另一些則沒有這種偏好。后者的貝殼形態(tài)會(huì)因木材種類不同導(dǎo)致的硬度不同而出現(xiàn)變化。水深也會(huì)影響貝殼形態(tài)，但是食木蛤科本身的貝殼形態(tài)又高度趨同，因此僅依靠貝殼形態(tài)很難將食木蛤定種，而水管等軟體結(jié)構(gòu)及其蛀道外部形態(tài)成為重要的分類依據(jù)。

Abditoconus brava/ Romano et a，2020

Abditoconus investigatoris。A–B. 正模TMAG E58320；C. TMAG E59292；D. 副模 2 TMAG E58316 / MacIntosh et al，2021

Spiniapex gilsonorum（TMAG E58450）/ MacIntosh et al，2021

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