---
title: Mosaic Longarm Octopus (Abdopus abaculus)
scientific_name: Abdopus abaculus
common_name: Mosaic Longarm Octopus
taxon: Cephalopods
conservation_status: DD - Data Deficient
published: 2024-11-02T18:52:40.323Z
updated: 2026-08-11T19:10:24.543Z
tags: Mosaic Longarm Octopus, Abdopus abaculus, Cephalopods, Red Sea, Marine Life, Diving
url: https://redseacreatures.com/taxon/invertebrate/molluscs/cephalopods/mosaic-longarm-octopus
---

# Mosaic Longarm Octopus (*Abdopus abaculus*)

## Quick facts

- **Group:** Cephalopods (*Cephalopoda*)
- **Size:** 3.3 cm
- **Weight:** 21 g
- **Depth:** 1-5 m
- **Diet:** Carnivore
- **Activity:** Cathemeral
- **Rarity:** Rare
- **Habitat:** Shallow rubble and coral fragments, close inshore
- **Reproduction:** Egg layer, Gonochoric, Semelparous
- **Conservation status:** DD - Data Deficient

## How to recognise it

- mosaic of dark gray to purple with cream and lilac spots
- very small, mantle barely 33 mm
- shallow rubble and coral fragments, often under 5 m
- may leave a shed arm writhing behind it

A pygmy octopus with a mantle of barely 33 mm (1.3 in), dark gray to purple with cream to lilac spots in a mosaic pattern. It lives in very shallow water, from the shoreline down to about 5 m (16 ft), on rubble and among coral fragments, and it is small enough that most divers who pass one will register a moving stone.

The second common name, drop-arm octopus, is the useful one. Members of this genus shed an arm when something grabs one, and the detached arm keeps writhing on the bottom for minutes: the nervous system of an octopus arm is largely local, and it can run its own movements without the brain. The predator stays with the moving piece while the animal leaves. The arm regrows.

Males court with posture and color and mate at arm's length, passing a sperm packet along a modified third arm. This is one of the few octopus genera where males have been recorded fighting and guarding females rather than mating opportunistically.

Everything else about it is unrecorded. It was described only in 1997, from Philippine material, and there is no published account of its diet, lifespan or breeding in the wild. The gaps here are real, not an omission.

## Also known as

- **English:** Mosaic Drop-arm Octopus, Mosaic Longarm Octopus, Mosaic Octopus
- **Italian:** Polpo mosaico
- **Portuguese:** Polvo-mosaico
- **Japanese:** カクレダコ

## Scientific synonyms

- *Octopus abaculus* M. Norman & Sweeney, 1997

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*Source: [Red Sea Creatures](https://redseacreatures.com/taxon/invertebrate/molluscs/cephalopods/mosaic-longarm-octopus)*
*Updated: August 11, 2026*