---
title: Divided Flatworm (Pseudoceros dimidiatus)
scientific_name: Pseudoceros dimidiatus
common_name: Divided Flatworm
taxon: Flatworms
published: 2023-12-27T01:06:11.207Z
updated: 2026-08-15T21:48:55.355Z
tags: Divided Flatworm, Pseudoceros dimidiatus, Flatworms, Red Sea, Marine Life, Diving
url: https://redseacreatures.com/taxon/invertebrate/worms/flatworms/divided-flatworm
---

# Divided Flatworm (*Pseudoceros dimidiatus*)

## Quick facts

- **Group:** Flatworms (*Pseudocerotidae*)
- **Size:** up to 8 cm
- **Depth:** 1-30 m
- **Diet:** Carnivore
- **Activity:** Diurnal
- **Rarity:** Uncommon
- **Habitat:** Reef and rubble, in the open in daylight
- **Reproduction:** Egg layer, Simultaneous hermaphrodite
- **Hazard:** Poisonous

## How to recognise it

- flat oval body, black with a bold orange-yellow median stripe and margin
- no visible organs, no segments - a sheet of tissue a millimeter thick
- swims by rippling the whole body edge like a flamenco skirt
- length up to 8 cm

A sheet of black and orange tissue about a millimeter thick, gliding over coral in broad daylight, with no shell, no spines and nothing between it and anything that wants to eat it.

It survives by being poisonous and saying so. Flatworms of this group carry potent toxins in the skin - in some species tetrodotoxin, the pufferfish poison - taken up from the prey they eat, and the bold pattern is the label. Fish that try one do not try a second.

When it needs to leave, it swims. The entire margin of the body ripples in waves and the animal lifts off the bottom and travels through open water like a flamenco skirt, which is startling the first time you see it.

And it is a simultaneous hermaphrodite with a habit worth knowing: two flatworms meeting fence with their penises, each trying to inject sperm into the other while avoiding being injected, because carrying the eggs is the expensive job. The loser bears the young.

## Also known as

- **English:** divided flatworm, symmetrical flatworm, tiger flatworm
- **French:** Ver plat tigre
- **Italian:** Platelminta giallonero, Platelminta tigre
- **German:** Symmetrischer Strudelwurm, Tiger-Plattwurm
- **Russian:** Тигровый псевдоцерос

---

*Source: [Red Sea Creatures](https://redseacreatures.com/taxon/invertebrate/worms/flatworms/divided-flatworm)*
*Updated: August 15, 2026*