Summary
Physical Description
Ecology
Life History & Behaviour
Anatomy & Physiology
Evolution & Systematics
Biogeographic Distribution
Conservation & Threats
References & Links | Life History & Behaviour
C. ungulatus belongs to Xanthoidea which is a superfamily within the infraorder Brachyura and that houses families Trapezia, Pilumnus and Panope. Brachyura is a large infraorder with species showing a wide variety of feeding and reproduction behavioural patterns, growth and species interactions.
Reproduction and Growth
A study by Mcdonald, (1982) covered the reproduction and growth of two crab species occupying an intertidal oyster habitat. Of both crab species studied Panopeus herbstii is from the Xanthid family and a close relative of C. ungulatus. P. herbstii females reach first reproduction at approximately 22mm carapace width, are ovigerous for six to seven months a year, carrying 3000 – 113000 eggs of 0.31mm in diameter and weighing 5.5µg, and undergo reproduction annually. With respect to observations of C. ungulatus, a female of just over half the size of my largest female (Bambi – 35mm) approximately 20mm found with thousands of black eggs. This fits in well with the findings of Mcdonald. An assumption of similarities in the reproductive cycles can be drawn from these close species, though egg size could be largely different due to the need for P. herbstii eggs to cope with potential desiccation. Due to finding only one C. ungulatus under 20mm it could be said that they share a similar growth cycle to P. herbstii reaching sexual maturity in approximately one year, this means that they cycle through all larval stages and grow approximately 20mm carapace width in just under a year. Meaning that the pelagic larvae that most crabs possess would have a short production phase.
Feeding
 C. ungulatus uses a technique known as scrubbing to accumulate food, (as seen in the video below). It mainly eats algae scraping it off the substrate of its habitat though the type of algae unknown a study on coral symbiont scrubbers revealed that red and green algae were preferred (Saisho et al. 1983). Though scrubbing for algae is their main technique some species have been known to engage in burrow storing of algal supplies or even echinoid and gastropod remains. Kyomo (1999) found that females showed a higher feeding rate than males, this could be due to their energy need for an annual reproductive cycle.
Species Interactions
From observations Cyclodius ungulatus isn’t an aggressive style of crab, with claws made for scraping and the toxicity of their body they don’t have or need to the capability to defend against many predators. There are often recordings of mutualistic relationships between crustaceans and their host corals, one documented was between a shrimp species Alpheus lottini and crab Trapesia serenei (McKeon et al. 2012). This study showed that each species were able to live, defend and provide beneficial protection against their hosts predation. Observing the behaviour of C. ungulatus it is possible for them to live in a mutualistic relationship with other crustaceans inhabiting corals, rubble or fouling environments.
Video: Grazing Xanthids (Cyclodius ungulatus) provided by youtube user jlpm87
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