Xenassiminea Nana: New Genus and Species of Assimineidae from Japan

Scientists have recently described and named a new snail species that is native to Japan and belongs to the family Assimineidae.

The species, called Xenassiminea nana, is the smallest among known assimineids and has a translucent, spiral shell.

It was first discovered more than three decades ago by Dr. Hiroshi Fukuda, an Associate Professor at Okayama University, but remained undescribed until now.

Dr. Fukuda published his findings in Molluscan Research.

What makes Xenassiminea nana unique?

(Photo : ISSOUF SANOGO/AFP via Getty Images)

Xenassiminea nana is a rare and peculiar gastropod species that lives in brackish water habitats such as estuaries and mangroves.

It is referred to as Ka-wa-tare-kawa-zanshō in Japanese, which means "the snail that crosses the river".

It has been labeled as "vulnerable" or "near threatened" in several government and local red lists due to its limited distribution and habitat loss.

Xenassiminea nana has some distinctive anatomical features that set it apart from other assimineids and gastropods. For example, it has distinct omniphoric grooves, which are furrows on the shell that allow the snail to breathe air when submerged.

It also has specific radular teeth, which are used for scraping food from surfaces. Its reproductive system and nervous system organization are also different from other assimineids.

One of the most striking features of Xenassiminea nana is its tentacular nerve, which runs parallel to the optic nerve and reaches a triangular bulge around each eye.

This is a unique trait that has not been seen in any other taxa within the family.

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How did Dr. Fukuda classify Xenassiminea nana?

Dr. Fukuda has been studying Xenassiminea nana since he first found it in 1992, when he was a fourth-year university student.

He realized that it was a member of the family Assimineidae, despite its morphological dissimilarity to other assimineids. Then, he decided to conduct a taxonomic revision of the family and to describe the new species in detail.

For the classification, Dr. Fukuda examined, cataloged, and deposited snail specimens across multiple collections and museums.

He used various methods to preserve the specimens, such as drying, neutral seawater formalin, or ethanol.

He also compared Xenassiminea nana with other assimineine members, such as Angustassminea sp. from Okinawa, which is another rare and undescribed species.

Dr. Fukuda named the new species Xenassiminea nana, which means "the dwarf foreign assimineid".

The genus name Xenassiminea reflects the fact that the species is not closely related to any other assimineid genera.

The species name nana comes from the Latin word "nanus", which means dwarf, and refers to the exceptionally small size of the species, which is only about 1.5 mm in shell height.

Dr. Fukuda hopes that his study will contribute to the conservation and understanding of Xenassiminea nana and other assimineids, which are often overlooked and understudied.

He also plans to continue his research on the diversity and evolution of the family Assimineidae.

What are the implications and challenges of Xenassiminea nana?

Xenassiminea nana is a remarkable example of the diversity and adaptation of gastropods, which are one of the most diverse groups of animals on Earth.

It shows how snails can evolve to survive in different environments and develop unique features that help them cope with various challenges.

It also reveals the complex relationships among different taxa within the family Assimineidae, which is still poorly understood and in need of further investigation.

However, Xenassiminea nana also faces many threats to its survival, such as habitat degradation, pollution, invasive species, and climate change.

Its small size and restricted distribution make it vulnerable to these factors, which could lead to its extinction.

Therefore, it is important to protect and monitor its habitats, as well as to raise awareness and appreciation of its existence and value.

Xenassiminea nana is not only a new snail species, but also a precious part of the natural heritage of Japan and the world.

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