This is an early access version, the complete PDF, HTML, and XML versions will be available soon.
Morphological and Molecular Evidence Revealed New Species in Mactra antiquata sensu lato
by
,
Fei Teng
1,†, 
Peizhen Ma
2,3,†,
Yang Zhang
1,
Jiazhen Zhang
1,
Yuan Zhang
1,
Jie Liu
1,* and
Haiyan Wang
4,* 1
National Maritime Museum of China, Tianjin 300450, China
2
State Key Laboratory of Mariculture Biobreeding and Sustainable Goods, Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao 266071, China
3
Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao Marine Science and Technology Center, Qingdao 266237, China
4
Laboratory of Marine Organism Taxonomy & Phylogeny, Shandong Province Key Laboratory of Marine Biodiversity and Bio-resource Sustainable Utilization, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Biology 2026, 15(2), 178; https://doi.org/10.3390/biology15020178 (registering DOI)
Submission received: 4 December 2025
/
Revised: 11 January 2026
/
Accepted: 14 January 2026
/
Published: 18 January 2026
(This article belongs to the Section Zoology)
Simple Summary
This study aimed to clarify the taxonomic status of Mactra antiquata sensu lato, which has long been controversial due to morphological and molecular variations. Samples newly collected from four Chinese coastal provinces were analyzed using integrated morphological and molecular methods. Results showed two distinct groups (N-group and S-group) with significant differences in shell ratios, pallial sinus orientation, and escutcheon shape. Molecular analyses (phylogeny, haplotype networks, genetic distances, ASAP, and ABGD) confirmed obvious genetic differentiation exceeding intraspecific thresholds. The S-group was identified as a new species, Mactra haiboensis sp. nov., distributed in the East and South China Seas. This study provides diagnostic criteria for the new species and lays a foundation for its targeted conservation and further research.
Abstract
Mactra antiquata sensu lato, a commercially important clam species in China, exhibits remarkable morphological and molecular diversity, which has led to the proposal of cryptic species within this complex. In the present study, specimens of M. antiquata sensu lato were collected from four coastal provinces (Shandong, Guangdong, Guangxi, and Hainan) of China, and an integrated comparative analysis was performed based on morphological traits and partial sequences of two mitochondrial genes (cytochrome c oxidase subunit I, COI; and 16S rRNA). Our results revealed that M. antiquata sensu lato could be clearly delineated into two distinct clades: the N-group (comprising specimens collected from Shandong in this study) and the S-group (including specimens collected from Guangdong, Guangxi, and Hainan), with significant intergroup differences. Morphologically, S-group individuals possessed relatively narrower shells (mean shell width-to-length ratio = 0.465) and shorter shells (mean shell height-to-length ratio = 0.781) compared to N-group conspecifics. Additionally, the pallial sinus of S-group clams extended directly toward the anterior adductor muscle, whereas that of N-group clams pointed to the region below the anterior adductor muscle. Furthermore, the escutcheon of N-group individuals was considerably more slender than that of the S-group. Phylogenetic trees and haplotype networks constructed based on both partial COI and 16S rRNA sequences further confirmed a deep genetic divergence between the two groups, with Kimura 2-parameter distances of 0.158 for COI and 0.084 for 16S rRNA. Collectively, these morphological and molecular lines of evidence strongly support the existence of cryptic species within M. antiquata sensu lato. By comparing the morphological characteristics of specimens in this study with the original description of M. antiquata, we herein propose that the S-group represents a new species, which we named M. haiboensis sp. nov. Our findings provide a scientific basis for the targeted conservation and further research of both M. antiquata and M. haiboensis sp. nov.
