Patelloida parva, Paran & Sasaki & Asakura & Nakano, 2025

Comparison of Patelloida parva n. sp. with Patelloida saccharinoides

The genetic characteristics of Patelloida parva n. sp. were compared with those of Patelloida saccharinoides , a tropical species exhibiting 93% genetic similarity. Although this study did not perform side-by-side comparisons between P. parva n. sp and P. saccharinoides , substantial morphological differences were observed based on the original description published on P. saccharinoides by Habe and Kosuge (1966). Below, we discuss the differences with the P. saccharinoides , justifying the recognition of P. parva n. sp. as a distinct species.

P. parva n. sp. exhibits a conical shell with 8–12 radial ribs of varying thickness. The major ribs are thicker, while thinner secondary ribs intersperse between the primary ribs, forming a distinctive stellate pattern. In contrast, P. saccharinoides ( Fig. S3 View Fig ) possesses six prominent radial ribs that are thicker and paired, projecting outward radially. Externally, P. parva n. sp. displays greyish-blue to brown reticulate markings with a whitish eroded apex. The ventral view reveals a smooth and lustrous interior with blue and yellow shadings on the apex and dark blue to black margins encircling the shell. In contrast, P. saccharinoides exhibits a dark outer coating with black margins except at the rib ends, and a uniformly white internal surface. Shell size also differs significantly. P. parva n. sp. is smaller in size, while P. saccharinoides has larger dimensions, with lengths of 36.3–40.4 mm, widths of 32.0– 35.5 mm, and heights of 8.5–11.2 mm (See Table S1 for shell dimensions of P. parva samples).

Despite a 93% genetic similarity between P. parva n. sp. and P. saccharinoides , mitochondrial 16S rRNA analysis revealed sequence divergence rates of 5.01%, a sufficient threshold to distinguish them as separate species. Phylogenetic analysis using Bayesian inference confirmed the monophyly of P. parva n. sp., clustering it with P. saccharinoides but maintaining clear genetic distinctiveness. In terms of ecological distribution, P. parva n. sp. is confined to the intertidal zones of Kochi and Wakayama Prefectures, Japan, with additional occurrences in Amami-Oshima Islands. Its distribution is influenced by the Kuroshio Current, which likely facilitated its migration from the tropics. The type locality of P. saccharinoides is in Zamboanga, Mindanao, Philippines.

However, the sequences of P. saccharinoides available in GenBank lack corresponding morphological data, raising the possibility that they do not represent the true P. saccharinoides as originally described by Habe and Kosuge (1966). Furthermore, no genetic sequences collected from the type locality of P. saccharinoides have been analyzed, increasing the risk of misidentification. Additional morphological and molecular studies, particularly involving specimens from the type locality, are necessary to confirm the genetic status of P. saccharinoides and its relationship to P. parva n. sp.