The Department of Invertebrate Zoology houses some of the most extensive and historically important metazoan and protozoan collections available to researchers today. The Department also contains the arachnid collection, but excludes mollusks, insects, deuterostomes and the "lophophorates." The holdings represent over one million specimens within 307,000 lots, with 7,663 primary types, plus several thousand secondary types. The Araneae collection is currently one of the largest in the world, with all major families represented. The crustacean collection is among the most important in the world. Other strengths are the Acari (including fossil material in Baltic amber), Myriapoda, Cnidaria and hexactinellid sponge collections.
The collections contain terrestrial and aquatic specimens from diverse geographical regions of the world. Many specimens were collected during the 19th and early 20th century expeditions, most significantly the “Thayer” to Brazil, the “Hassler” around the coast of South America, the “Blake” and “Atlantis” both to the Atlantic and Caribbean, the “Challenger” and “Albatross” to many Pacific regions, and the U.S. Geological Surveys of the Territories.
More recent marine acquisitions include North Atlantic specimens from various National Marine Fisheries Service cruises, the reference collection for the Massachusetts Water Resource Association Boston Harbor clean-up and the Howard Sanders deep-sea collections from the Woods Hole Oceanographic Institution.