Critter of the Week: Dagnaudus petterdi – the antlered crab

You may remember our critter of the week number 175 – Psolus antarcticus (Philippi, 1857), the limpet-like sea cucumber?  This was featured while half of our collection team were at sea investigating marine food webs on the Chatham Rise. While they did come across some of these sea cucumbers (to the bewilderment of some people who thought they may be a type of ascidian or even a nudibranch!), we also came across the spiny, long-legged antlered crab.  

Critter of the Week number 175 – Psolus antarcticus (Philippi, 1857)

The Antlered crab Dagnaudus petterdi (Grant, 1905) is distinguished by its antler-like horns to either side of the eyes with a simple rostrum in the middle, and small hooks at the end of the last pair of legs, which are usually held above the carapace. [Owen Anderson, NIWA. TAN0905 - Chatham Rise Graveyard Seamounts]

Carrier crabs

Dagnaudus petterdi (Grant, 1905), also known as the antlered crab, is a member of the Homolidae family which contains 15 genera known as carrier crabs. Carrier crabs have the ability to hold their last pair of walking legs above their carapace in a sub-dorsal position and use them to carry other objects - even other invertebrates such as sea urchins, corals and sponges. This could be as an anti-predatory behavior or perhaps food-carrying. See this video of carrier crabs in action:

video.nationalgeographic.com

Adaptions

The antlered crab lives on the continental slope, between 180 to 540 m depth, and are distributed on the East Coast, Northland to Fiordland and Snares Islands, New Zealand. They are also found in Australia and New Caledonia. Its carapace is covered in tubercles and spines, and has characteristic spiny long thin walking legs, which are probably used to hold itself above the soft mud on which it lives. In addition to having the ability to lift its back legs over its carapace, the legs of Dagnaudus petterdi feature distinctive small hooks, which help it grasp objects.

In this image the last pair of legs are bent slightly forward and the characteristic black claws are clearly seen. This specimen was caught from the Chatham Rise between 305 to 316 m depth during a recent marine food webs survey. [Diana Macpherson, NIWA, TAN1511 Fisheries Oceanography III 2015 survey]

Close-up view of the branched antlers, spiny carapace, and prominent bulbous eyes on short eye-stalks of Dagnaudus petterdi (Grant, 1905). This specimen was caught from the Chatham Rise between 305 to 316 m depth during a recent marine food webs survey. [Diana Macpherson, NIWA, TAN1511 Fisheries Oceanography III 2015 survey]

Close-up of the antlered crabs swollen palms (enlarged in older males) and black fingers. This specimen was caught from the Chatham Rise between 305 to 316 m depth during a recent marine food webs survey. [Diana Macpherson, NIWA, TAN1511 Fisheries Oceanography III 2015 survey.]

References:

McLay, C.L. (1988). Brachyura and crab-like Anomura of New Zealand. Leigh Laboratory Bulletin No. 22. 463 p

Tracey, D.M.; Anderson, O.F.; Naylor, J.R. (Comps.) (2011). A guide to common deepsea invertebrates in New Zealand waters. New Zealand Aquatic Environment and Biodiversity Report No. 86. 317 p.