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| Physalia mikazuki Yongstar, Ochiai & Lewis Ames, collected from Gamo Beach, Sendai City, Miyagi Prefecture, Japan. in Yongstar, Ochiai, Nugraha, Tan, Totsu, Sato-Okoshi et Lewis Ames. 2025. |
The discovery of Physalia mikazuki sp. nov. from the temperate waters of Gamo Beach, Sendai Bay (Miyagi Prefecture) in the Tohoku (northeast) region of Japan, represents a significant addition to the taxonomic and ecological understanding of this genus. Morphological analysis reveals key diagnostic traits, distinguishing it from all known Physalia species. Phylogenetic analyses of the 16S rRNA gene and COI (cytochrome c oxidase subunit 1) regions further confirm its classification as a distinct species, forming a well-supported monophyletic clade separate from other Physalia species. Oceanographic data and Lagrangian particle trajectory simulations suggest that P. mikazuki may have dispersed northward via the recent 100 km northward extension of the Kuroshio Current (KE) in tandem with record-breaking sea surface temperature changes (SST) of more than 2°C in the Tohoku region between 2022 and 2024. Long-term monitoring confirmed no previous reports of Physalia at the type locality of Gamo Beach, Sendai City (Tohoku) prior to 2023, indicating a likely recent introduction. Molecular barcode sequences matching samples from both Pakistan and Mexico indicate a broad Indo-Pacific connectivity for the new species. The occurrence of P. mikazuki sp. nov. in the Tohoku region poses potential ecological and public health concerns, particularly due to its predation on fish larvae and risk of envenomation during beach recreation. This study underscores the importance of integrative experimental design combining taxonomy, molecular data, and oceanographic modeling to understand species range shifts and cryptic diversity in a changing ocean.
Keywords: Portuguese man-of-war, new species, ecosystem change, Kuroshio Extension (KE), distribution range
Phylum Cnidaria Verrill, 1865
Subphylum Medusozoa Peterson, 1979
Class Hydrozoa Owen, 1843
Subclass Hydroidolina Collins, 2000
Order Siphonophorae Eschscholtz, 1829
Family Physaliidae Brandt, 1835
Genus Physalia Lamarck, 1801
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| Morphological characteristics of Physalia mikazuki sp. nov. collected from Gamo Beach, Sendai City, Miyagi Prefecture, Japan. Type 112960 (Tohoku University Museum).; Central image: Entire colony displaying the gas-filled pneumatophore and trailing tentacles (scale bar = 5 cm).; (A) Lateral view of the pneumatophore with a well-defined wrinkled crest and transparent, sail-shaped float.; (B) Close-up of the dorsal surface beneath the pneumatophore, highlighting clusters of gonodendra, tentacular palpons, and gastrozooids with yellow-tipped oral regions.; (C) Multiple principal tentacles exhibiting characteristic coiled morphology.; (D) Zooid clusters divided into the posterior zone (right), containing six zooid clusters (I–VI) and a protozooid (PZ), and the main zone (left), with densely packed tripartite zooid groups extending aborally. Colony orientation is indicated (anterior, posterior, dorsal, ventral).; (E) Close-up view of the gastrozooids elongate with distally swollen, balloon-like yellow tips, highlighting their feeding structures. Photographs taken of live specimens under natural and aquarium lighting to preserve color and morphology. |
Physalia mikazuki sp. nov. Yongstar, Ochiai & Lewis Ames
Diagnosis: Physalia mikazuki sp. nov. Yongstar, Ochiai & Lewis Ames is distinguished from other members of the genus Physalia by a combination of morphological traits: Pneumatophore length range 9.25–72.4 mm, with maximum known size smaller than that reported for P. physalis (8.1–134 mm) but overlapping with P. utriculus. Coloration of the crest is bluish with deep blue to purple hues and membrane is a translucent bluish-green (vs. dark green/carmine in P. physalis, blue and clear-glassy in P. utriculus, transparent with green patch at anterior apex in P. minuta). Up to six zooid clusters are present in the ...
Distribution: Tohoku and Kanto regions of Japan; Pakistan and Mexico.
Type locality: Gamo Beach, Sendai City, Miyagi Prefecture, Japan.
Etymology: The Japanese word “mikazuki” refers to the “crescent moon” shape of the warrior helmet worn by Samurai Masamune Date (1567 – 1636) of the Tohoku region who founded Sendai City. Vernacular “mikazuki no eboshi” (Japanese), “crescent helmet man-of-war” (English).
Chanikarn Yongstar, Yoshiki Ochiai, Muhammad Izzat Nugraha, Kei Chloe Tan, Ayane Totsu, Waka Sato-Okoshi and Cheryl Lewis Ames. 2025. Physalia mikazuki sp. nov. (Phylum Cnidaria; Class Hydrozoa) blown into Japan’s northeast (Tohoku) at the whim of Marine Ecosystem Change. Front. Mar. Sci. 12:1653958. DOI: doi.org/10.3389/fmars.2025.1653958 [30 October 2025]
