Exploring the Ross Sea: Investigating Peracarid Crustaceans and Aplacophoran Molluscs

As the RVIB Nathaniel B. Palmer steams south toward the Ross Sea, I find myself reflecting on the incredible biodiversity hidden beneath the surface in the frigid Antarctic waters. The Kocot lab specializes in studying marine invertebrates, and on this expedition—NBP25-01—we are particularly excited about sampling peracarid crustaceans and aplacophoran molluscs using an epibenthic sledge. We hope our efforts will contribute to a deeper understanding of their diversity, phylogeny and biogeography.

Peracarid Crustaceans: Piecing Together Evolutionary Relationships
Peracarida is an incredibly diverse and ecologically important group of crustaceans that includes amphipods, isopods, tanaids, mysids, and cumaceans (comma shrimp). Dr. Sarah Gerken has already introduced cumaceans in a previous blog post, highlighting their unique morphology and lifestyles. Building on that, our research focuses on resolving the higher-level phylogeny of Peracarida—an effort that requires robust sampling across multiple taxa and habitats.

Our project, in collaboration with Dr. Regina Wetzer and other colleagues (see www.peracarida.org), aims to use genome scale molecular data to reconstruct evolutionary relationships among major peracarid lineages. Despite their abundance and ecological significance in deep-sea and polar environments, many aspects of peracarid phylogeny remain poorly understood. By collecting fresh specimens from the Ross Sea, we hope to fill critical gaps in taxon sampling and refine our understanding of peracarid evolution.

One of the fascinating aspects of peracarids is their brood pouch (or marsupium), a characteristic that distinguishes them from other crustaceans. This adaptation allows them to protect their young through early development, a key advantage in the extreme Antarctic environment. Additionally, their varied feeding strategies—ranging from scavenging and filter-feeding to predation—highlight their ecological versatility. Through our work, we aim to clarify how different peracarid groups are related and explore how their diversification patterns correlate with Antarctic environmental shifts over evolutionary timescales.

Aplacophoran Molluscs: Shedding Light on an Understudied Molluscan Lineage
Another major research focus of the Kocot lab (www.kocotlab.com) is the biodiversity and phylogenetics of aplacophoran molluscs, a little-known group of worm-like mollusks that lack shells and instead are covered in microscopic calcareous spicules. These animals are divided into two main clades: Solenogastres and Caudofoveata, both of which inhabit the deep sea and play vital roles in benthic ecosystems. While they may not be as charismatic as larger mollusks like squids or scallops, they are evolutionarily significant because they offer key insights into the early evolution of mollusks as a whole.

Our previous work on aplacophorans during the NBP20-10 and NBP23-03 cruises, as documented in blog posts by Emily McLaughlin, Carmen Cobo, Franzi Bergmeier, and Chandler Olson, has already provided exciting discoveries. We are eager to expand on that research by collecting additional specimens from the Ross Sea. Our goal is to use DNA barcoding and morphological analyses to better understand their biodiversity and transcriptome sequencing and genome skimming to better understand their evolutionary relationships.

One of the challenges of studying aplacophorans is their fragility and cryptic nature. They are often overlooked in benthic samples due to their small size and delicate bodies. However, the epibenthic sledge we are using on this cruise is well-suited for capturing these elusive animals. By targeting different regions and depths, we hope to collect a diverse array of specimens that will help us refine the molluscan tree of life.

The Importance of Antarctic Biodiversity Research
Both peracarid crustaceans and aplacophoran mollusks are key components of Antarctic benthic ecosystems, yet much remains to be learned about their diversity, distribution, and evolutionary history. By combining traditional taxonomy with cutting-edge genomic techniques, we aim to uncover new species, resolve long-standing phylogenetic questions, and better understand how these organisms have adapted to life in one of Earth’s most extreme environments.

As we begin our sampling in the Ross Sea, we are filled with anticipation for what we might discover. Every expedition brings new surprises, and the invertebrate life hidden beneath the Antarctic ice holds secrets that can reshape our understanding of evolution, biogeography, and biodiversity. Aside from these focal taxa, I aim to collect specimens of diverse other taxa to enrich the collections at the Alabama Museum of Natural History and benefit other researchers beyond our team. Stay tuned for updates as we share our findings from NBP25-01!

Dr. Kevin Kocot
University of Alabama