# Chaetoderma shenloong mollusc hosts dracosphera with over 1,600 bacteria per cell

- Published: 2026-11-15 15:28 UTC
- Section: Life & Health › Biology & biochemistry
- Tags: dracosphera, Chaetoderma shenloong, cold seep symbiosis, sulphur-oxidising bacteria, shell-less mollusc, South China Sea, chemosynthesis, digestive gland, Nature Communications
- URL: https://realtech.media/news/rt-7cee4facd6115e3b17b98a06_chaetoderma_shenloong_mollusc/

**Researchers described a microscopic 10–15 µm structure with over 20 membrane layers in the digestive gland of a shell-less mollusc from a South China Sea cold seep.**

![Chaetoderma shenloong mollusc hosts dracosphera with over 1,600 bacteria per cell](https://realtech.media/media/2026/11/721227072e388faf.webp)
*Muy Interesante*

According to Muy Interesante, a research team has described a spherical structure, named dracosphera ("dragon ball" in Latin), in the digestive gland of the shell-less mollusc Chaetoderma shenloong. The structure is 10–15 micrometres across and is surrounded by more than 20 membrane layers [1]. The animal was found buried in sediments with almost no oxygen at a cold seep in the South China Sea. The study was published in Nature Communications [1].

## Structure and symbiotic bacteria

The dracosphera is not a geological formation: it is located inside the animal's cells. For scale, a human hair is about 70 micrometres thick. Chaetoderma shenloong belongs to the caudofoveates, a group of aplacophorans that, unlike snails or clams, have no shell [1]. Cold seeps are areas of the seabed where fluids rich in chemical compounds, including methane, emerge at relatively low temperatures.

Inside the dracosphera there are symbiotic bacteria: on average, more than 1,600 per host cell [1]. The bacteria are chemosynthetic, that is, they obtain energy from chemical reactions rather than sunlight. They oxidise sulphur compounds rather than feeding on methane, and the genomic and spatial evidence collected in the study is compatible with this metabolism [1]. Nothing in the work shows that the mollusc "eats methane".

## Reorganised anatomy and open questions

Much of the mollusc's digestive tube is reduced or absent, while the digestive gland is greatly enlarged and has a reticulated, net-like structure. This is where the dracospheres and their bacteria are housed [1]. The authors suggest the gland may have shifted from processing external food to maintaining and managing symbionts, but anatomy alone does not show how much the animal depends on its bacteria.

The membrane layers vary notably in total thickness between specimens. The researchers propose that they may regulate the diffusion of oxygen to the bacteria, which would matter in nearly anoxic sediment. This has not been demonstrated in a living animal; it is a hypothesis based on the observed architecture and habitat [1].

Several points remain unestablished. It is not known which molecules pass from the bacteria to the mollusc, or in which direction nutrients are exchanged. It is suggested that the host may digest part of its bacteria to recover nutrients, but the whole process has not been observed directly. It is also unknown whether the association is obligatory, how bacteria are passed between generations, and how their number in each cell is controlled. The dracosphera is not equated with an organelle such as the mitochondrion. Answering these questions would require direct measurements of oxygen and nutrient flows, chemical tracer experiments, physiological analyses under controlled conditions and comparisons with related species [1].

## Sources

1. [Muy Interesante](https://muyinteresante.okdiario.com/ciencia/bola-de-dragon-molusco.html)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-7cee4facd6115e3b17b98a06_chaetoderma_shenloong_mollusc/