Brisingida

Abstract: Seamounts are important deep ocean entities that serve as reservoirs for varied types of habitats and fauna. During the Chinese cruises in the northwestern Pacific seamount areas, a new starfish species of order Brisingida, Astrolirus patricki, was found at 1,458-2,125 m depth. All specimens of the new species were observed in situ attaching on hexactinellid sponges, suggesting a possible close relationship between the two taxa. A. patricki sp. nov. is the second known species of the genus, characterized by the abutting plates in the intercostal integument, separated first pair of adambulacral plates and densely distributed proximal spines. Phylogenetic analyses were conducted for order Brisingida to incorporate the new species as well as Hymenodiscus cf. fragilis (Fisher, 1906), Freyella cf. attenuata Sladen, 1889 and two Brisinga spp., for which we present the molecular data for the first time. Phylogenetic trees suggest a close relationship between A. patricki sp. nov. with Brisinga species rather than with Hymenodiscus species, which is inconsistent with morphological taxonomy. This study highlights the distinct morphological and ecological characters of the new species and provides new data for future investigation on Brisingida phylogeny.

Abstract: Starfish (phylum Echinodermata) are ecologically important and diverse members of marine ecosystems in all of the world's oceans, from the shallow water to the hadal zone. The deep sea is recognized as an extremely harsh environment on earth. In this study, we present the mitochondrial genome sequence of Mariana Trench starfish Freyastera benthophila, and this study is the first to explore in detail the mitochondrial genome of a deep-sea member of the order Brisingida. Similar to other starfish, it contained 13 protein-coding genes, two ribosomal RNA genes, and 22 transfer RNA genes (duplication of two tRNAs: trnL and trnS). Twenty-two of these genes are encoded on the positive strand, while the other 15 are encoded on the negative strand. The gene arrangement was identical to those of sequenced starfish. Phylogenetic analysis showed the deep-sea Brisingida as a sister taxon to the traditional members of the Asteriidae. Positive selection analysis indicated that five residues (8 N and 16 I in atp8, 47 D and 196 V in nad2, 599 N in nad5) were positively selected sites with high posterior probabilities. Compared these features with shallow sea starfish, we predict that variation specifically in atp8, nad2, and nad5 may play an important role in F. benthophila's adaptation to deep-sea environment.

Abstract: Freyastera (Downey, 1986) is a derived group of deep-sea starfish in the order Brisingida with 6 arms and slender ambulacral plates, whose taxonomy and phylogeny have rarely been investigated. In this research, two new species of Freyastera are reported from the northwest Pacific Ocean, both characterized by fairly long and numerous lateral spines and the presence of furrow spines. Freyastera delicata n. sp. is further distinguished from other species by having 6–8 spinelets arranged in a transverse line on each abactinal arm plate. Freyastera basketa n. sp. is similar to the Atlantic species Freyastera sexradiata (Perrier, 1885), but differs from the latter by the presence of pedicellariae on the abactinal surface and number of mouth spines and lateral spines. A revised key to Freyastera and potential Freyastera spp. from the genus Freyella (Perrier, 1885) is provided. Phylogenetic analysis was conducted using available molecular data for the order Brisingida. The intraspecific and interspecific divergence within Freyastera are recognized from a COI genetic distance matrix, in which some abnormal intraspecific distances are found between the known species, which might indicate the existence of cryptic species and an underestimated diversity in the genus. A phylogenetic tree of Brisingida is constructed based on a concatenated sequence dataset of COI, 16S and H3 gene fragments. The tree supports the affinity of Freyastera and Freyella, which together form a crown clade within the order. The global distribution and in situ observations of Freyastera are discussed to provide information on their ecological characteristics and diversity.