Lamarckdromia is a genus of marine crabs belonging to the family Dromiidae, commonly known as sponge crabs or carrier crabs. These crabs are notable for their unique camouflage strategy, wherein they carry living sponges, ascidians, or other marine organisms on their carapaces.
Etymology
The genus name Lamarckdromia honours Jean-Baptiste Lamarck, a prominent French naturalist and early proponent of evolution. The suffix "-dromia" is characteristic of the Dromiidae family, derived from the Greek dromos, meaning "running" or "course," though in the context of these crabs, it often refers to the family itself.
Taxonomy and Classification
- Kingdom: Animalia
- Phylum: Arthropoda
- Subphylum: Crustacea
- Class: Malacostraca
- Order: Decapoda
- Infraorder: Brachyura
- Family: Dromiidae
- Genus: Lamarckdromia
Description and Characteristics
Members of the genus Lamarckdromia share the general characteristics of other Dromiidae crabs, but possess distinct morphological features:
- Camouflage: Their most striking feature is the habitual carrying of living sponges, ascidians (sea squirts), or other sessile invertebrates on their dorsal surface. They meticulously cut and shape these organisms to fit their carapace, securing them with their specialized last two pairs of legs.
- Legs: The last two pairs of pereiopods (walking legs) are typically reduced in size and modified to be dorsally directed, often subchelate (pincer-like), allowing them to grasp and hold the carried camouflage material firmly.
- Carapace: The carapace (dorsal shell) is generally rounded or subglobose, providing a stable base for the carried material. Its texture and ornamentation vary between species.
- Size: Species within Lamarckdromia can vary in size, from a few centimeters to over ten centimeters in carapace width.
Habitat and Distribution
Lamarckdromia species are found in marine environments across tropical and subtropical regions worldwide, including the Indo-Pacific, Atlantic, and other oceans. They typically inhabit soft substrates or rocky areas where suitable camouflage organisms, such as sponges, are abundant. Their depth range can vary from shallow coastal waters to deeper continental shelves.
Ecology and Behavior
The relationship between Lamarckdromia crabs and their carried organisms is often considered a form of commensalism or mutualism:
- Protection: The primary benefit for the crab is effective camouflage, making it difficult for predators to spot. The carried organism may also deter predators through chemical defenses (e.g., toxic sponges) or unpalatability.
- Mobility for the organism: The carried sponge or ascidian gains mobility and access to new feeding grounds or environmental conditions that it would not experience as a sessile organism.
- Active Selection: The crabs actively select, cut, and shape the organisms they carry, demonstrating a sophisticated behavioral adaptation. If the original camouflage material is lost or outgrown, the crab will seek and acquire a new one.
Selected Species
As a diverse genus, Lamarckdromia includes several recognized species, such as:
- Lamarckdromia globosa (Stimpson, 1858)
- Lamarckdromia excavata (Stimpson, 1858)
- Lamarckdromia johnstoni (Guinot & Macpherson, 1987)
- Lamarckdromia rathbunae (Richardson, 1949)