Xinzheng Li

A poorly known callianassid ghost shrimp species, Praedatrypaea modesta (De Man, 1905), is redescribed and illustrated based on new material recently collected off the south coast of Hainan Island, northern continental shelf of the South China Sea. Genetic data were obtained and compared with other six congeners. With the inclusion of this species, the monophyly of Praedatrypaea Poore, Dworschak, Robles, Mantelatto & Felder, 2019 is reevaluated. The inferred phylogenetic trees, based on two matrices (4-gene and 21-gene), both support the monophyly of this genus and its placement as sister taxon to all other genera of Callianassidae Dana, 1852.

This study describes two new species collected from deep-sea environments in the Indo-West Pacific. Hyalonema (Cyliconema) dexiangi sp. nov. , collected from the Indian Ocean, is characterized by distinctive finger-like protuberances on the body surface, the presence of choanosomal pentactins, the co-occurrence of micropentactins and microhexactins, and the absence of mesamphidiscs. Hyalonema (Cyliconema) subconica sp. nov. , sampled from a seamount in the western Pacific Ocean, is distinguished by the presence of pinular diactins, a unique combination of choanosomal spicules (diactins, pentactins, and hexactins), and the presence of basalia bearing two-toothed anchors. In addition to their morphological distinctions, molecular phylogenetic analyses based on 16S rDNA sequences indicate a close genetic relationship between the two species.

Munidopsis species represent some of the dominant macrobenthos in cold seep habitats of the northern South China Sea. Earlier studies documented high abundances of M. verrilli Benedict, 1902 at Site F cold seep and M. lauensis Baba & de Saint Laurent, 1992 at Haima cold seep. However, comparative morphological and genetic analysis of additional materials from the deep waters of California, Manus Basin, and southern Okinawa Trough now indicate that those specimens in the South China Sea require taxonomic revision: the specimens at Site F should be M. longispinosa Cubelio, Tsuchida & Watanabe, 2007 and the specimens at Haima cold seep belong to M. ryukyuensis Cubelio, Tsuchida & Watanabe, 2007. Complementary descriptions of M. ryukyuensis , M. longispinosa and M. verrilli , as well as their geographic distributions, are provided to facilitate future identification.

Microbial communities at Site F cold seep, ubiquitous in both the environment and the associated fauna, demonstrate clear habitat-specific partitioning. Metagenomic sequencing and binning demonstrated a striking partitioning of microbial taxa at the cold seep: whereas the sponge-associated microbiome was distinctly enriched with specialized sulfur- and methane-oxidizing bacteria that were rare in the environment, it simultaneously exhibited a significantly reduced archaeal content, lower α-diversity, and a simpler overall community structure compared to the sediment and seawater communities. Distinct evolutionary lineages and varying abundances were observed among the microbiomes from seawater, sediment, and sponges. Furthermore, their Metagenome-Assembled Genomes (MAGs) exhibited significant differences in genomic features, including genome size and GC content. The sponge-associated microbiome exhibits lower diversity but maintains a high abundance of key functional genes, particularly those involved in sulfur cycling (e.g., apr, dsr, metZ), indicating enhanced metabolic efficiency in energy conservation and nutrient acquisition. This study reveals that the seawater, sediment, and sponge-associated microbiomes exhibit genome simplification and functional specialization in the cold seep environment, with varying lifestyles driving structural optimization and functional remodeling of the symbiotic microbiomes.

Cold seep sponges typically reside in the carbonate rock areas surrounding the vents, often comprising only a few individuals of a limited number of species. Previous limited studies have indicated that sponges living in seeps or vents host chemolithotrophic microorganisms, including sulfur-oxidizing bacteria (SOB) and methane-oxidizing bacteria (MOB), regardless of their feeding habits. This suggests that they may utilize compounds from their environment. However, when multiple sponge species are found co-occurring in a single sponge ground sharing identical environmental and material conditions, it remains unclear how their symbiotic community structure will behave. Specifically, it is uncertain whether the community will exhibit greater similarity or, as seen in most studies, demonstrate host specificity. We utilize metagenomics and binning analysis to characterize six new sponge species belonging to two classes and two distinct dietary habits, all discovered in the same cold seep. Our findings reveal that their associated microbial communities, primarily composed of SOB and MOB from the phylum Proteobacteria, exhibit a high abundance of groups with the same chemosynthetic functions. Binning recovered diverse, novel MAGs (metagenome-assembled genomes) primarily dominated by order PS1 (SOB) and order Methylococcales (MOB). This similarity extends beyond the dietary habits and higher taxonomic levels of the sponge hosts. Phylogenetic and abundance difference analyses of MAGs indicate significant host specificity in the selection of symbiotic microbial species among different sponge species. Notably, these MOB and SOB exhibit potential novelty within their clade compared to known taxa. Furthermore, the genomes of these SOB and MOB contain abundant functions related to their adaptation to the chemoautotrophic environment and symbiotic lifestyle within the cold seep. The chemosynthetic environment shapes the high relative abundance of key functional groups that dominate the symbiotic community, while the species differences among host sponges determine the strain selection within these groups. The metabolic functions expressed by this "convergence with divergence" community structure collectively endow the holobionts with the ability to adapt to the cold seep environment.

A recently collected specimen of the rare deep-sea nematocarcinid genus Segonzackomaius Burukovsky, 2011 from the Philippine Basin is new to science and we revealed that the material previously reported as S. altus (Spence Bate, 1888) from Taiwan also belongs to this new species, based on a DNA sequence comparison. The new species S. sursus sp. nov. differs from S. altus by having a relatively shorter but ascending rostrum, and a longer telson, which distinctly exceeds the uropodal endopod. An identification key to the three known species of Segonzackomaius is provided. The multi-gene analyses do not support the monophyly of Nematocarcinus A. Milne-Edwards, 1881 because S. sursus sp. nov. forms a robust clade with N. lanceopes Spence Bate, 1888 and this clade is very separated from other species of Nematocarcinus. Nevertheless, a more extensive molecular study on the phylogenetic relationships amongst the taxa within the family Nematocarcinidae Smith, 1884 is necessary for a better comprehension of its evolution.

The genus Typhlonida Macpherson & Baba in Machordom et al. 2022 is a group of munidid squat lobsters typically found in deep waters. This study describes and illustrates a new species, Typhlonida cocoensissp. nov., from a seamount area in the eastern Pacific. Typhlonida cocoensissp. nov. is closely related to T. sanctipauli (Henderson, 1885) but can be readily distinguished from the latter by its relatively small eyes, narrow anterior margin of the thoracic sternite 4, lack of granules on the lateral surfaces of sternite 7, and unarmed anterior branchial regions dorsally. In addition to morphological comparisons, genetic distance and phylogenetic analyses were used to support the recognition of this new species. The phylogenetic positions of the Typhlonida and Antillimunida species from the eastern Pacific are discussed.