Hantazuia sp. 1

Overview

An unidentified species within the genus Hantazuia (family Hantazuidae). Collected from Okinawa, Japan. Multilocus barcoding (COI / 16S / H3) places it closest to Hantazuia yugoikedai (Honshu, Jogashima) but distinct from all three currently described species, suggesting a fourth Hantazuia species candidate.

Description

The body has a yellowish coloration similar to H. yugoikedai. Unlike H. yugoikedai, however, the notum becomes black in this species, providing a reliable external diagnostic. The sympatric H. imagawai also consistently shows a dark notum, presumably because its thin body wall allows the underlying digestive gland to show through; this species and H. imagawai are therefore distinguished by the shape and arrangement of the cerata rather than by notal coloration.

Distribution

Known from Okinawa, Japan. Sympatric with H. imagawai.

Three-marker integrated analysis

Pairwise distances against the three named Hantazuia species at COI, 16S, and H3 are as follows.

At COI, divergence to H. yugoikedai is 14.5-14.8% (= 85.2-85.5% identity), to H. imagawai 15.75% (= 84.25% identity), and to H. kimotoi 16.67% (= 83.33% identity). These all slightly exceed the 12.3-13.1% inter-species range previously reported among the three named Hantazuia species.

At 16S, BLAST-based divergence from named Hantazuia species is approximately 10%. At H3, divergence is 2.45% (= 97.55% identity) and essentially equidistant from all three named species.

All three markers consistently indicate a divergence slightly beyond the inter-species range within Hantazuia, clearly distinguishing this specimen as a divergent lineage among the genus. The COI signal placing it closest to H. yugoikedai is consistent with the external morphology, which resembles H. yugoikedai in its yellowish coloration.

Remarks

Hantazuidae fam. nov. and Hantazuia gen. nov. were recently erected to accommodate small aeolids from the north-western Pacific along the Japanese coast, with three named species (H. yugoikedai and H. kimotoi from Jogashima, Honshu; H. imagawai from Okinawa). The present specimen is positioned as a fourth species candidate within this framework: collected in Okinawa yet phylogenetically positioned closer to the H. yugoikedai + H. kimotoi subclade rather than to the sympatric H. imagawai. The combination of yugoikedai-like morphology, Okinawan distribution, and sympatry with H. imagawai represents a typical sympatric cryptic divergence pattern that warrants formal description.

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