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| Delectopecten thermus Lin, in Lin, Peng, Chen, Xu et Qiu, 2025. |
Abstract
Delectopecten is a small genus of the family Pectinidae (Bivalvia: Pectinida) that remains poorly studied in terms of both morphology and phylogeny. Here, we describe the first member of this genus from deep-sea hydrothermal vent ecosystems, D. thermus sp. nov., based on morphological investigations and molecular analyses of a specimen collected from the Higashi–Ensei vent field (962-m depth) in the northern Okinawa Trough. Morphologically, this new species resembles D. vancouverensis and D. gelatinosus in shell size, shape, auricle size and sculpture. However, D. thermus sp. nov. can be distinguished from its congeneric species (including 9 extant and 12 fossil species) by its unequal auricles (the anterior one being larger than the posterior), inwardly recurved anterior auricle of the left valve and a large byssal notch angle of ~90°. Comparisons of genetic sequences from three mitochondrial and three nuclear gene fragments supported the placement of the new species in the genus Delectopecten. Further phylogenetic analyses using these gene markers support that Delectopecten is monophyletic and positioned as an early diverging clade of the family Pectinidae. Additionally, the mitogenome of D. thermus sp. nov. was assembled and annotated, a first for its genus – revealing significant divergences in gene order compared to other pectinids. The 16S rRNA amplicon analysis of the gill tissue indicated that this vent-dwelling scallop does not exhibit symbiosis with chemosynthetic bacteria. A key to all known species of Delectopecten is provided to aid the identification of species in this understudied genus.
Keywords: bivalvia, deep sea, Delectopecten, heterotrophy, Higashi–Ensei, hydrothermal vent, identification key, new species, Okinawa Trough, Pectinidae, systematics, taxonomy, trophic mode.
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| Delectopecten thermus sp. nov., holotype (NSMT-Mo 79569). (a, b) External and internal views of the left valve. The ‘6’-like structure on the outer surface is the calcareous tube of an annelid worm. (c, d) External and internal views of the right valve. |
Order: PECTINIDA Gray, 1854
Family: PECTINIDAE Rafinesque, 1815
Subfamily: CAMPTONECTINAE Habe, 1977
Delectopecten Stewart, 1930
Type species: Delectopecten vancouverensis Whiteaves, 1893
Delectopecten thermus Lin, sp. nov.
Etymology: The species epithet ‘thermus’ means ‘thermal’ in Latin, refer-ring to its hot vent habitat.
Yi-Tao Lin, Ying-Bei Peng, Chong Chen, Ting Xu and Jian-Wen Qiu. 2025. Integrative Morphological, Mitogenomic and Phylogenetic Analyses reveal New Vent-dwelling Scallop Species. Invertebrate Systematics. 39, IS24091. DOI: doi.org/10.1071/IS24091
