Red triangle slug

The red triangle slug (Triboniophorus graeffei) is a species of large air-breathing land slug, a terrestrial pulmonate gastropod mollusk in the family Athoracophoridae, the leaf-veined slugs.

Red triangle slug
Two individuals of the green form of Triboniophorus graeffei, in the forest in Chatswood West, New South Wales. The slug on the right is starting to become active, the other is in the contracted state.
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Subclass: Heterobranchia
Superorder: Eupulmonata
Order: Stylommatophora
Superfamily: Athoracophoroidea
Family: Athoracophoridae
Subfamily: Aneitinae
Genus: Triboniophorus
Species:
T. graeffei
Binomial name
Triboniophorus graeffei

This large (up to 15 centimetres (5.9 in)), often colorful and striking-looking species is found in eastern Australia. It is Australia's largest native land slug.[2] It is a common part of the fauna.

Triboniophorus graeffei is the type species of the genus Triboniophorus.[3] A closely related species is the as-yet-unnamed Triboniophorus sp. nov. 'Kaputar'.

Distribution
Distribution map of Triboniophorus graeffei

This slug species occurs on the east coast of Australia, from New South Wales to Queensland.[4]

An affiliated bright pink species, Triboniophorus aff. graeffei, are found exclusively on Mount Kaputar.[5]

Solem (1959)[3] mentioned a possible introduction of this species to the New Hebrides, but no material was available to confirm it.

Habitat

Red triangle slugs are found in damp situations in various habitats, including city gardens, forests, woodland and heaths.[2]

Life habits
Triboniophorus graeffei with grazing marks from its radula, on the trunk of a Sydney Blue Gum, near Dungog, Australia

These slugs graze on algae which grows on the surface of the smooth bark of some eucalyptus trees and on rocks. Sometimes the slugs enter houses[4] and have been known to graze on the mold that grows on bathroom walls.[2][6]

This species of slug has been found to have an unusual defensive mechanism. It can secrete a kind of sticky mucus (different from the slippery slime secreted when it moves) that is strong enough to glue predators down for days. The glue is strongest in wet conditions and becomes less sticky as it dries. The cells responsible for secreting the glue are located across the dorsal surface.[7][8]


Description

These slugs have two, not four, tentacles, and like other leaf-vein slugs, they have an indented pattern on their dorsum which resembles that of a leaf. The body length is up to 14 cm.

They are very variable in color. Individual slugs can be white, off-white, yellow, dark or light grey, beige, pink, red, or olive green.[4] Each of the color forms have a red (possibly orange, magenta, or maroon) triangle on the mantle surrounding the pneumostome, and a red line at the edge of the foot. The texture of the dorsum of the slug can be smooth or very rough.

Juveniles lack the typical red foot border and red triangle of the adults but have three dark grey stripes running down the dorsal surface of their body and have the triangular mantle shield outlined with grey.[9]

Research is currently being carried out in an attempt to determine if some of the different colourations may actually represent different species or subspecies.[4]

Various shots of Triboniophorus graeffei on the bark of Sydney Blue Gums, near Dungog, Australia, showing color variation, varying degrees of contraction and body shape.

  • Close-up of a pale pink individual with the pneumostome open and a narrow body, tentacles fully extended
  • An off-white individual with a very pale "red triangle"
  • A beige individual with a very wide body and a pale orange "triangle" and foot edge. Tentacles partially retracted
  • Two individuals, one fully contracted and with pneumostome closed
  • Same two individuals from the side showing the body shape in profile
  • Same two individuals, the previously contracted one has retreated to a less exposed position among old flakes of bark
  • Juvenile Red Triangle Slug on moist Hawkesbury Sandstone, Chatswood West, Australia

References
  1. Humbert A. (December 31) 1863. Études sur quelques mollusques terrestres nouveaux ou peu connus. Mem. Soc. Phys. Nat. Hist. Geneve, 17, (1), 109-128. Description at page 119.
  2. Red Triangle Slug Fact File. Australian Museum, 2009, accessed 22 February 2009.
  3. Solem A. 1959. Systematics of the land and fresh-water mollusca of the New Hebrides. Fieldiana Zoology, volume 43, number 1, Chicago Natural History Museum, page 45-46
  4. (June) 2004. Red Triangle Slug Diversity. An Australian Museum Website, Australian Museum, accessed 22 February 2009.
  5. Stanisic J. 2010. Australian Land Snails Volume 1
  6. Stephanie Pain (July) 2000. Hate housework? Can't find a reliable cleaner? Try a slug. New Scientist Magazine, Melissa Kaplan's Herp Care Collection, Last updated April 19, 2007. Accessed 22 February 2009.
  7. Le Page, Michael. "Slime-fighting slug can superglue enemy frogs to trees for daysSlime-fighting slug can superglue enemy frogs to trees for days". New Scientist. Retrieved 22 February 2019.
  8. Gould, John; Valdez, Jose W.; Upton, Rose (2019). "Adhesive defence mucus secretions in the red triangle slug (Triboniophorus graeffei) can incapacitate adult frogs". Ethology. 125: 587–591. doi:10.1111/eth.12875.
  9. pers. comm. Michael Shea, Australian Museum

Further reading
  • (in German) Pfeiffer W. 1898. Anatomische und histologische Bemerkungen über Triboniophorus Graeffei Humbert. Sitzber. Ges. natf. Freunde, Berlin.

Photographs on the life history etc.:

Photographs of the various different color forms:

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