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Tetralia nigrolineata

A small crab that lives among the branches of corals of the genus Acropora, on which it depends. 4 5 It can be recognised by the black band along the front and side edges of its carapace. 3 Like others in its genus, it probably feeds on coral mucus and detritus. 6

Tetraliidae
Tetralia nigrolineata

At a glance

Data from the scientific sources listed at the bottom.

Depth in the wild

2–10 m

0 m2 m4 m6 m8 m10 m

Conservation

NEDDLCNTVUENCREWEX

IUCN Red List: not evaluated. Red List data taken from SeaLifeBase and GBIF. 2 11 It does not appear in the CITES lists checked on Species+. 10

Where it lives

Red SeaWestern Indian OceanEastern Indian OceanCentral Indo-PacificWestern PacificCentral PacificEastern PacificWestern AtlanticEastern AtlanticMediterranean

Indo-Pacific. 2 Recorded in the Seychelles, Mozambique and Réunion, in the Gulf of Thailand, Malaysia, Indonesia, Japan, the Solomon Islands, Australia and New Caledonia; the type locality is in Queensland. 3 It is also known from Singapore, Guam and the Philippines, and from northern Taiwan since 2016. 4 WoRMS adds Mayotte, the East China Sea and French Polynesia. 1

How to recognise it

Tap a number on the photo: the key explains what to look for.

1234
  1. 1Black band sharp, along the front and side edges of the carapace 3
  2. 2Pale line thin, edging the black band 3
  3. 3Claw uniform in colour, like the legs 3
  4. 4Dark spot on the joint of the propodus, a segment of the leg 3

Life in the wild

Where it is found

It lives among Acropora branches. 4 5 In Taiwan it was collected at 2-10 m on Acropora hyacinthus and Acropora digitifera 4, at Lizard Island at 2-4 m on Acropora valida. 8 In the literature it goes down to 52 m 4, and SeaLifeBase gives 1-66 m. 2 It is not entirely exclusive: in one study it also turned up on pocilloporid corals 7, and a not-yet-adult individual was found on a sea fan. 4

What it eats

The data are at genus level: Tetralia ingests coral mucus together with the detritus it contains, and on its legs it has small brushes and two rows of bristles, called a 'feeding comb'. 6 The Aquarium of the Pacific adds that coral crabs use special appendages to stimulate the coral to produce more mucus. 9

Behaviour

Tetralia and Trapezia crabs proved to be the most effective symbionts at keeping crown-of-thorns starfish away from the coral. 7 Tetralia mainly pinches the tube feet and, unlike the larger Trapezia, causes no lasting damage. 7 These crabs also remove detritus and sediment from the colony. 8 9

Reproduction

On each Acropora valida colony studied at Lizard Island there was one breeding pair. 8 In the genus they usually live in pairs, one per colony. 6 For coral crabs in general, gestation lasts about a month in the laboratory. 9

In the aquarium

From the experience of the BallingMania community.

Community rating
Level in the tank
lowmediumhigh
Coral compatibility
lowmediumhigh
Aggression
lowmediumhigh
Care difficulty
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Original sheet

Tetralia nigrolineata is a small, easily recognised symbiotic crab, marked by a black band that divides the body horizontally; as often happens, this band gives it its name, Nigro Linea or Black Line.

This crab is about 1 cm long, and its size lets it move nimbly through the colony of the coral that hosts it. It feeds on mucus, which it gathers with the "combs" on its legs, and on food scraps that stick to it; it keeps the colony clean and deters and keeps away pests.

It does not feed on pests (a real shame!); however, it has been observed preying on flatworm eggs (not bad).

Geographical area: Indo-Pacific. Diet: symbiotic commensal

Species sheet written by Tiozzo Matteo Brasiola

Did you know?

It has been suggested that Tetralia crabs eat the flatworm that attacks Acropora and its egg capsules, but this is only a possibility: it has not been observed. 8
Tetralia species look very much alike, and in the past several were confused under the name Tetralia glaberrima; colours in life matter a lot. 5 This very species started out as a form of T. glaberrima. 1
Plate-shaped Acropora colonies can host many crabs of the genus: in one, 27 males and 16 females were counted. 6

Sources

  1. DecaNet (2026). Tetralia nigrolineata Serène & Pham, 1957. World Register of Marine Species.
  2. SeaLifeBase (2026). Tetralia nigrolineata. SeaLifeBase.
  3. Naturalis Biodiversity Center (2026). Tetralia nigrolineata, Crabs of Japan. Naturalis.
  4. Limviriyakul P., Tseng L.C., Hwang J.S., Shih T.W. (2016). Anomuran and Brachyuran Symbiotic Crabs in Coastal Areas between the Southern Ryukyu arc and the Coral Triangle. Zoological Studies.
  5. Trautwein S.E. (2007). Four new species of coral crabs belonging to the genus Tetralia Dana, 1851 (Crustacea, Decapoda, Brachyura, Tetraliidae). Zootaxa.
  6. Castro P. (1976). Brachyuran Crabs Symbiotic with Scleractinian Corals: A Review of their Biology. Micronesica.
  7. Pratchett M.S. (2001). Influence of coral symbionts on feeding preferences of crown-of-thorns starfish Acanthaster planci in the western Pacific. Marine Ecology Progress Series.
  8. Rawlinson K.A., Stella J.S. (2012). Discovery of the Corallivorous Polyclad Flatworm, Amakusaplana acroporae, on the Great Barrier Reef, Australia. PLOS ONE.
  9. Aquarium of the Pacific (2023). Coral crabs, Online Learning Center. Aquarium of the Pacific.
  10. UNEP-WCMC (2026). Search for Tetralia nigrolineata in the CITES lists. Species+.
  11. GBIF Secretariat (2026). Tetralia nigrolineata, IUCN Red List category. GBIF.

Sources checked on 5 November 2026. Community texts and ratings are kept separate from the scientific data.

View the original sheet (Italian)All species