Libinia spinosa

Libinia spinosa is a majoid crab found in mud and sand bottoms of the Southwestern Atlantic and Pacific oceans. It is a generalist feeder on organisms such as algae, sponges, cnidarians, mollusks, polychaetes, crustaceans, and small fish. It commonly engages in a symbiotic relationship with the medusa Lychnorhiza lucerna.

Libinia spinosa
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Malacostraca
Order:	Decapoda
Suborder:	Pleocyemata
Infraorder:	Brachyura
Family:	Epialtidae
Genus:	Libinia
Species:	L. spinosa
Binomial name
Libinia spinosa Milne Edwards, 1834

Description

Libinia spinosa is a member of the crab superfamily Majoidea which are commonly known as the spider crabs.^[1] The carapaces of this organism can measure up to 89 mm and its leg span can be up to 568 mm.^[2] The number of median spines of Libinia spinosa can vary, with 7 being the most common number, but Libinia spinosa with 5, 8, and 10 median spines are also seen commonly.^[2] Testes are visibly flat, transparent structures that are coiled anteriorly.^[3]

Range and habitat

Libinia spinosa is commonly found at both mud and sand bottoms in the Southwestern Atlantic and Pacific oceans.^[2][4] It inhabits Southwestern Atlantic waters ranging from Nova Scotia to Argentina.^[2][4] In the Pacific Ocean, it is found off the coasts of the United States, Baja California, Galápagos Islands, Hawaii, Peru, and Chile.^[4] The depths at which this organism is found at range from the intertidal zone to 170 m. It prefers sediment that contains both silt and clay.^[5]

Reproduction

Libinia spinosa engage in precopulatory courting using both olfactory and tactile cues, indirect sperm transfer is common.^[6] Females have been shown to exhibit sexual selection with their preference for larger males.^[4] The trait that has been shown to be most highly correlated with mate acquisition for males is large cheliped size.^[7] Males have been shown to exhibit mate guarding where they will maneuver their chelipeds around the female and fight off other males.^[4] Precopulatory mate guarding is exhibited significantly longer than postcopulatory mate guarding.^[4] Males breed with females by turning the female upside down and below them and subsequently inserting their gonopods into the female's gonophores. Male copulatory organs consist of a long first gonopod and a short stout second gonopod.^[4] Females produce 1-3 offspring for each breeding season.^[4]

Life cycle

Floating Lychnoriza lucerna

Libinia spinosa with peteropods retracted for protection

Prezoeal phase

Libinia Spinosa's total length in this phase is 0.8 mm and the larva is encased in a cuticle. Its rostrum and dorsal spine are folded. The maxillipeds have terminal, retracted setae. This stage lasts 3 to 5 minutes.^[8]

Zoeal phase

Libinia spinosa has 2 stages in the zoeal phase of its larval cycle. In the zoeal phase, Libinia spinosa contains a carapace with one rostral and one dorsal spine, seven setae are present. The abdominal somite 2 of the zoeal phase has 2 dorsolateral projections while the abdominal somite 3 lacks dorsolateral projections. The abdominal somites 3 and 4 of the zoeal phase have postero-lateral processes. There are 10 marginal setae and 1 apical setae on the scaphognathite.^[9]

Megalopa phase

The megalopal phase of Libinia spinosa contains 1 stage.^[9] The rostrum in this phase is deflected ventrally and carapaces contains spines/tuberance.^[9] There are 2 maxillule endopod setae, 0 maxilla endopod setae, 4 first maxilliped epipod setae, and 6 third maxilliped setae.^[9]

Ecology

Libinia spinosa can be classified as a generalist species when it comes to diet.^[9] It consumes both mobile and nonmobile prey.^[10] It feeds on organisms such as algae, poriferans, cnidarians, mollusks, polychaetes, crustaceans, and small fish.^[9]Libinia spinosa does not have commercial value but is unintentionally caught in prawn trawls, an activity which has led to a decline in its population.^[5] Libinia spinosa carries epibionts such as sea anemones on top of its carapaces.^[5]

Symbiotic relationship with Lychnorhiza lucerna

Libinia spinosa has been shown to engage in a symbiotic relationship with the medusa Lychnorhiza lucerna, mainly during its juvenile stages.^[11][12][5] Libinia spinosa burrows itself in the subgenital pockets of Lychnorhiza lucerna.^[11]Libinia spinosa is protected from predators by the stinging cnidocytes of Lychnorhiza lucerna and also ingests food particles collected by Lychnorhiza lucerna.^[11] Additionally, this relationship allows Libinia spinosa to move through the environment while conserving its own energy.^[5] There is no clear benefit to Lychnorhiza lucerna hosting Libinia spinosa so their symbiotic relationship is likely a form of commensalism.^[12][11]