Diversity and potential parentage of molluscan (and likely-molluscan) eggs from the Aleutian Trench

Many deep-sea molluscs are in taxonomic groups known to deposit demersal egg capsules, but limited information is available on the morphology of molluscan egg capsules from abyssal and hadal depths. During the 2022 “AleutBio” expedition (R/V SONNE, SO293) to the Aleutian Trench, we collected egg capsules from depths ranging between 4,220 and 7,142 m. Morphological analysis revealed eight distinct egg types, ranging from translucent capsules to large, grape-like yolky eggs, and those containing no discernible development to visible embryos. Six of these could be tentatively attributed to known taxa based on co-occurrence and morphology: caenogastropod egg capsules with protoconchs morphologically matching the buccinid Bayerius knudseni (Bouchet & Warén, 1986), different capsules likely belonging to Cancellariidae and Eulimidae, stalked yolky eggs postulated as being from the rare trench volutid Tenebrincola frigida Harasewych & Kantor, 1991, and droplet-shaped egg causules consistent with cirrate octopuses of which the emperor’s dumbo octopus (Grimpoteuthis imperator Ziegler & Sagorny, 2021) is the only species known with certainty from the region. Two other egg types — a small ovate egg with metallic sheen and a cluster of seven grape-like capsules — remain taxonomically unresolved and may or may not be molluscan. Our findings represent the first records of molluscan egg capsules from abyssal to hadal parts of the Aleutian Trench and add to the limited knowledge of deep-sea mollusc spawns.