The Non-Insect Arthropods collection contains a great variety of invertebrate specimens of the phylum Arthropods included in eight large groups with category of class; it ranges from marine organisms such as Pycnogonids (sea spiders or Pantopoda) or Xiphosura (horseshoe crabs, true living fossils), to other typically terrestrial specimens such as Arachnida, Chilopoda, Diplopoda, Symphylans and Pauropods (commonly called centipedes, millipedes and garden centipedes); there are also crustaceans - mostly marine and freshwater specimens, and a few terrestrial, as it is the case with many isopoda. The collection is particularly strong in Arachnids and Crustacea, which are also the most morphologically and ecologically diversified groups. The Arachnids are representative of 17 orders. The most commonly known are araneids (spiders), scorpions, opiliones and acari; acari represent seven orders, including ectoparasites species such as ticks, which can transmit serious illnesses. Other important groups in the arachnids are the pseudoscorpions, the solifuges (camel spiders) and the thelyphonida (whip scorpions). Crustaceans show a huge morphological variety and inhabit different marine, freshwater and terrestrial ecosystems. There are sessile forms (Cirripedia, such as balanus, barnacles and smooth gooseneck barnacles), and forms with bivalve shells (ostracods) or without shell (amphipoda); there are specimens of the planktonic species (copepods); others are parasitic (rhizocephala), terrestrial (many of these are isopods) and specimens of great size and resilient calcareous shell such as the stomatopods (squila mantis shrimp) and decapods (crabs, lobster, European lobster, etc.).

As we mentioned before, the collection is strong in Crustaceans and Arachnids, but also in centipedes and millipedes. There are at least 2,760 represented species, most of them Crustaceans and Arachnids. Regarding the type material, there are 330 species comprised of 1,405 specimens. 69% of the specimens are terrestrial or from freshwater ecosystems, and 30% are marine. Over 37,000 of the marine specimens are native to the Spanish coasts; nearly 1,300 come from the Pacific Ocean (mostly the Philippines, Chile and Panama) and 500 from the Caribbean Sea (Venezuela and Cuba). There are around 70 specimens from the Southern Ocean, mainly Pycnogonids, Amphipods and Decapods. The collection houses 4,800 specimens from cavernous ecosystems, among which we may find the Arachnids, Chilopoda, Diplopoda and Crustaceans (Amphypoda, Isopoda and Bathynellacea mainly), with 146 types (27 holotypes) from caves across Spain - the Cantabrian coast, Navarre, Levante and Burgos, among other provinces. There are over 3,000 microscope slides and around 600 specimens. Most specimens of the historic collection are dry preserved.