# Morphological, Molecular and Phylogenetic Characterization of Ceratomyxa nemiptera sp. nov. (Myxozoa: Ceratomyxidae) Infecting Nemipterus virgatus Houttuyn, 1782 in the East China Sea

## TL;DR

A new myxosporean parasite was discovered infecting a commercially important fish in the East China Sea, adding to the known diversity of these tiny organisms.

## Contribution

The discovery and characterization of a new Ceratomyxa species infecting Nemipterus virgatus in the East China Sea.

## Key findings

- The new species has a crescent-shaped body with two polar capsules and distinct genetic material.
- Phylogenetic analysis shows it is closely related to Ceratomyxa arcuata but genetically distinct.
- This is the first report of a Ceratomyxa species infecting Nemipterus virgatus.

## Abstract

Myxosporean parasites are a large group of tiny organisms that infect both marine and freshwater fish, and identifying their species can be tricky due to their small size and variable shapes. Ceratomyxa, a large genus of myxosporeans, mostly infects the gallbladders of marine fish, and scientists now use a combination of morphological characteristics, infection site, host and genetic data to identify species of Ceratomyxa. Nemipterus virgatus, an economically important fish in southeastern Chinese coastal fisheries, is a known myxosporean host, but little is known about these parasites in the East China Sea. In our study, we found a new Ceratomyxa species (Ceratomyxa nemiptera sp. nov.) in the gallbladders of N. virgatus from the East China Sea. This new parasite has a crescent-shaped body with two spherical polar capsules near its front end, and its genetic material is distinct from other known myxosporeans, being most closely related to Ceratomyxa arcuata. This is the first time a Ceratomyxa species has been found infecting N. virgatus, adding to current knowledge of myxosporean diversity in the East China Sea and helping protect this important commercial fish.

A newly discovered myxosporean parasite was described from the gallbladder of Nemipterus virgatus Houttuyn, 1782 collected from the East China Sea. Mature myxospores are crescent-shaped with shell valves that taper gradually toward rounded ends. Each myxospore contained two sub-spherical polar capsules located near the anterior end, closely aligned along the suture line. The mature myxospores measured 6.2 ± 0.6 (5.4–6.9) μm in length and 44.8 ± 4.6 (38.5–53.1) μm in thickness. Polar capsules measured 2.8 ± 0.2 (2.4–3.1) μm in length and 2.3 ± 0.2 (1.9–2.6) μm in width, with polar filaments coiled in 2–3 turns. The small subunit ribosomal DNA (SSU rDNA) sequence of Ceratomyxa nemiptera sp. nov. was distinct from all known myxosporeans, showing the highest similarity (93.56%) and the shortest genetic distance (0.0637) with Ceratomyxa arcuata Thélohan, 1892. The phylogenetic analysis revealed that C. nemiptera sp. nov. was positioned within a later-diverging lineage, forming a sister-group relationship with a clade containing C. arcuata and Ceratomyxa cretensis Kalatzis, Kokkari & Katharios, 2013. This is the first report of a Ceratomyxa species infecting N. virgatus.