The arrow crab (Stenorhynchus seticornis) is a saltwater invertebrate that looks something like an underwater daddy long-legs. It moves surprisingly quickly for its ungainly appearance, and uses its muscular legs to keep predators at bay. They grow to a length of about 6". Scientific classification - Wikipedia /**/ @import /skins/monobook/IE50Fixes. ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria Placozoa Bilateria Acoelomorpha Orthonectida Rhombozoa ?Myxozoa Superphylum Deuterostomia    Chordata (vertebrates, etc. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - Trilobites (extinct) Subphylum Chelicerata Arachnida - Spiders, Scorpions, etc. ... Classes Remipedia Cephalocarida Branchiopoda Ostracoda Maxillopoda Malacostraca The crustaceans (Crustacea) are a large group of arthropods (55,000 species), usually treated as a subphylum. ... Orders Not necessarily a complete list: Leptostraca Stomatopoda Bathynellacea Thermosbaenacea Mysidacea Cumacea Amphipoda Isopoda Tanaidacea Euphausiacea Amphionidacea Decapoda Peracarida The Malacostraca are the largest subgroup of crustaceans, and include most of the animals that non-experts recognise as crustaceans, including the decapods (such as crabs, mole crabs, lobsters and true... Suborders Either suborders: Natantia Reptantia or suborders: Dendrobranchiata Pleocyemata The decapods or Decapoda are a group of crustaceans within the class Malacostraca. ... Infraorders Caridea Stenopodidea Reptantia, divided into: Polychelida Achelata Glypheoidea Astacidea Thalassinidea Anomala Brachyura Pleocyemata is a sub-order of decapod crustaceans, erected by Martin Burkenroad in 1963. ... In biology, binomial nomenclature is a standard convention used for naming species. ... 1788 was a leap year starting on Tuesday (see link for calendar). ... The Phalangids or Opiliones (better known as harvestmen or daddy longlegs) are eight-legged invertebrate animals belonging to the order Opiliones in the class Arachnida, in the subphylum Chelicerata of the phylum Arthropoda. ...

When kept in an aquarium, arrow crabs, while notorious for eating fish and becoming destructive in reef aquariums, can nonetheless be helpful. They are well-known for eating fireworms and other aquarium pests.