# Expanding Knowledge of Sea Pen (Octocorallia: Pennatuloidea) Diversity and Distribution Through Integrative Taxonomy: Insights From Hong Kong's Coastal Waters

## TL;DR

This study uses DNA and physical traits to identify nine sea pen species in Hong Kong, including three new ones, improving understanding of their diversity and distribution.

## Contribution

The study introduces three new sea pen species and provides new DNA sequences and phylogenetic insights for Hong Kong's sea pens.

## Key findings

- Nine sea pen species were identified in Hong Kong using molecular and morphological methods.
- Three new species (Cavernularia solaris, Lituaria triscleromorpha, and Virgularia exilis) were described.
- Phylogenetic analysis grouped the species into three well-supported clades.

## Abstract

Sea pens (Octocorallia: Scleralcyonacea: Pennatuloidea) are widespread but remain under‐documented in the Northwest Pacific. Using a combined molecular (MutS‐ND2‐28S rRNA) and morphological approach, we analysed sea pen samples collected from Hong Kong's urban waters. MutS sequences at a 0.3% divergence threshold and ASAP automatic delimitation resolved nine species across three families and four genera for Hong Kong specimens, consistent with phylogenies inferred from concatenated datasets (MutS‐ND2‐28S rRNA), which recovered nine species in three well‐supported clades within Pennatuloidea. Morphological examinations (colony form, zooid arrangement, axis shape, sclerite shape and size) corroborated species boundaries. We described three new species (Cavernularia solaris sp. nov., Lituaria triscleromorpha sp. nov., and Virgularia exilis sp. nov.) and updated the morphological descriptions of four previously known species. Additionally, we compared these species with sea pens reported from other regions, particularly Japan and Palau. By discovering new species and new distribution ranges, providing new DNA sequences, and clarifying phylogenetic placements for Hong Kong's sea pens, this work augments species inventories and contributes to ongoing revisions of Pennatuloidea systematics and biogeography in the Northwest Pacific.

Based on a combined molecular and morphological analysis, this study identifies nine sea pen species in Hong Kong's waters, including three newly described species. The findings provide new DNA sequences and clarify phylogenetic relationships, support revisions to Pennatuloidea systematics, and update species distributions in the Northwest Pacific.