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| Harcledo toyoshioae Kodama, Watabe, Nakaguchi & Wakabayashi, 2026 |
Abstract
Deep-sea visual environments show extreme gradients in light intensity, driving divergence in eye morphology. In the order Amphipoda, such specializations are documented in pelagic hyperiideans, whereas deep-sea Eusiridae remain poorly known. During a bathypelagic survey in Japan, we collected a eusirid amphipod with conspicuously enlarged eyes. Integrative taxonomy, using morphology and four DNA barcoding regions, shows that it represents a new species of the monotypic genus Harcledo Barnard, 1964, described here as Harcledo toyoshioae sp. nov. It is characterized by markedly enlarged eyes that cover most of the lateral head and meet across the dorsal midline, and by a distinctive maxilla 1 armature. Phylogenetic analyses place H. toyoshioae sp. nov. within Eusiridae but leave its relationships to H. curvidactyla unresolved, owing to the lack of sequence data. Comparisons with historical records suggest rapid diversification of eye size within this clade and indicate that it is unlikely to be governed by depth or pelagic–benthic mode alone. We propose that the enlarged eyes are plausibly associated with a pelagic lifestyle in dim mid-water habitats, while noting that this interpretation remains tentative. Our findings highlight visual specializations in deep-sea eusirids and the value of combining new collections, historical literature, and molecular data when reassessing deep-sea taxa.
Key words: bathypelagic, deep sea, Harcledo, Kagoshima, Tanegashima Island, visual specialization
ORDER AMPHIPODA Latreille, 1816
FAMILY EUSIRIDAE Stebbing, 1888
Harcledo Barnard, 1964
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| Harcledo toyoshioae sp. nov., paratype female, 18.8 mm, NSMT-Cr 33350, ethanol preserved specimen, photographs for head and pereonites 1–2: A, dorsal view; B, lateral view. |
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| Harcledo toyoshioae sp. nov., fresh specimens, lateral view: A, holotype ovigerous female, 21.6 mm, NSMT-Cr 33349; B, paratype female, 18.8 mm, NSMT-Cr 33350. |
Harcledo toyoshioae sp. nov.
DISTRIBUTION: Known only from type locality, North Pacific Ocean off Tanegashima Island, Kagoshima, Japan.
HABITAT: Bathypelagic zone (about 1200 m deep).
ETYMOLOGY: The new species is named after TRV Toyoshio Maru. The specific name is a noun in the genitive case.
Masafumi Kodama, Hiroto Watabe, Kazumitsu Nakaguchi and Kaori Wakabayashi. 2026. A New Species of Giant-eyed bathypelagic eusirid Amphipod (Crustacea: Amphipoda: Eusiridae) from the western North Pacific. Systematics and Biodiversity. 24(1); 2659885. DOI: doi.org/10.1080/14772000.2026.2659885 [05 Jun 2026]
