---
title: Brown-lined Paper Bubble (Hydatina physis)
scientific_name: Hydatina physis
common_name: Brown-lined Paper Bubble
taxon: Opisthobranchia
published: 2026-08-11T13:46:58.951Z
updated: 2026-08-11T14:12:55.104Z
tags: Brown-lined Paper Bubble, Hydatina physis, Opisthobranchia, Red Sea, Marine Life, Diving
url: https://redseacreatures.com/taxon/invertebrate/molluscs/opisthobranchia/brown-lined-paper-bubble
---

# Brown-lined Paper Bubble (*Hydatina physis*)

## Quick facts

- **Group:** Opisthobranchia (*Opisthobranchia*)
- **Size:** up to 6 cm
- **Depth:** 0-20 m
- **Diet:** Carnivore
- **Activity:** Nocturnal
- **Rarity:** Uncommon
- **Habitat:** Shallow sand and rubble flats, often near seagrass
- **Reproduction:** Egg layer, Simultaneous hermaphrodite

## How to recognise it

- thin rounded white shell ruled with dense fine brown-black spiral lines
- huge cream body edged with a wavy pink-white frill, far too big for the shell
- no rhinophores standing up, only a flat shield over the head
- length up to 6 cm

A thin white shell ruled with dense brown-black spiral lines, carried by a cream body so large it cannot possibly fit back inside, edged all around with a wavy frill in pink and white. Up to 6 cm (2.4 in) of it crossing open sand at night, and one of the most photographed animals on any Red Sea night dive that includes a sand flat.

The flat shield over the head is what the group is named for and what it is for: a plow. Headshield slugs burrow just under the surface, and the shield keeps sand out of the mantle cavity while the animal moves through it, which is why none of them have the standing rhinophores that make a nudibranch look like a rabbit. Everything about the body is built to slide.

It hunts worms. The prey are burrowing bristle worms, tracked through the sand and swallowed, and the search is chemical: this slug reads the water and the sediment through a groove along the front of the head rather than looking for anything. The eyes are two black dots buried in the tissue and see little more than light and shade.

## Also known as

- **English:** brown-line paperbubble, green paperbubble, green-lined paperbubble
- **German:** Meeresrose
- **Russian:** Гидатина полосатая

## Scientific synonyms

- *Bulla atrolineata* Schröter, 1804
- *Bulla physis* Linnaeus, 1758
- *Bulla quoyana* A. d'Orbigny, 1841
- *Bulla staminea* Menke, 1853
- *Hydatina filosa* Schumacher, 1817

## Range

Angola, Cape Verde, Coral Sea, Fiji, Gabon, Indian Ocean, Lord Howe and Norfolk Islands, Madagascar, Mozambique, New Caledonian Exclusive Economic Zone, New Zealand, North Atlantic Ocean, Republic of Mauritius, South Africa, Tanzania, Tasman Sea, Vanuatu, Vietnam

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*Source: [Red Sea Creatures](https://redseacreatures.com/taxon/invertebrate/molluscs/opisthobranchia/brown-lined-paper-bubble)*
*Updated: August 11, 2026*