Extinct Invertebrates

To the list of recently extinct invertebrates

The Invisible Majority: Invertebrate Animals

Invertebrates (Invertebrata), as the name suggests, are characterized by the fact that they have no spine, in contrast to vertebrates (Chordata). This group includes a variety of organisms, including insects. Also invertebrates are, for example, spiders, snails, mussels, jellyfish, octopuses, scorpions, crustaceans, starfish, worms, corals or tardigrades. The exact number of invertebrate species on Earth is difficult to determine, as many species have not yet been discovered or scientifically described. It is estimated that there are millions of invertebrate species, with more than 95 percent of all animal species being invertebrates.

The diversity of invertebrate species allows them to inhabit a wide range of habitats that span various ecosystems. Some live in hydrothermal vents, on seabeds, or in coral reefs, while others occur in freshwater habitats such as rivers, lakes, or wetlands. In addition, invertebrate animals are also found in terrestrial habitats such as forests, meadows, deserts, and the arctic tundra. Some species have adapted to extreme conditions, such as the dryness of the desert or the cold of the polar regions.

This diversity and the often small body size of invertebrate animals make it difficult to accurately determine their conservation status. The International Union for Conservation of Nature (IUCN) has listed 380 invertebrate species as extinct, including 81 insect species. Most of these extinct species (296) are mollusks (Mollusca) such as snails, mussels, octopuses, and squids. It is assumed that many more invertebrate species have become extinct, as the IUCN is extremely cautious in its assessments and lists some species as “critically endangered” even though they have not been detected for over 100 years.

With the IUCN Red List update in October 2024, five more snail species of the genus Partula were classified as extinct. This means that of the 93 tree snails from Polynesia listed by the IUCN, 32 are now classified as “extinct.” Another 9 species are currently considered extinct in the wild, 26 as endangered, 18 as highly endangered, and 3 as vulnerable.

Habitat loss – one of the greatest threats

The reasons for the disappearance of invertebrate animals are as diverse as the animals themselves and range from habitat loss to the threat of parasites. A major factor is often human intervention in their habitats, whether through deforestation, mining, or urbanization. The overexploitation of resources such as overgrazing, overfishing, or the collection of animals for trade also contributes to the disappearance of species. Climate change and pollution further exacerbate the situation by impairing the living conditions of the animals and making them more susceptible to disease.

Some invertebrate species live only in a single small place, and if this habitat is destroyed, it leads to the extinction of the species. This is what happened to the Pasadena freshwater shrimp: The body of water in which it lived was completely destroyed by channelization and urbanization. The Rose Bowl stadium now stands on the site where the shrimp species was discovered in 1897.

Another example is the Lake Pedder earthworm, which occurred exclusively in Lake Pedder, a lake in Tasmania, died out in 1972 immediately after the construction of dams on the lake. The former sandy beaches around the body of water in which the earthworm lived are now under water.

The Brazilian giant earthworm, which grew to be over two meters long, probably also had a very limited distribution area, so that habitat loss led to its extinction at the beginning of the 20th century. The Cascade funnel-web spider, endemic to Tasmania, also likely disappeared around 1926 due to urban developments that destroyed its habitat.

Extinct Invertebrates by Invaders

Endemic species that only occur on islands are particularly at risk. The destruction of their habitats and the introduction of animals and plants often lead to their demise. The list of extinct species that were once native to islands such as the Seychelles or Hawaii is enormously long.

Before humans settled the Hawaiian Islands, there were about 750 species of tree snails there. Today, most of them are considered endangered or already extinct. Of the 41 nocturnal snail species of the genus Achatinella, which live exclusively on the island of Oahu, at least 16 are extinct. Two examples are Achatinella buddii, which has not been sighted since 1900, and Achatinella apexfulva, of which the last specimen died in 2019.

The main reasons for the disappearance, in addition to the collection of snails and the loss of their habitat on the island, are introduced invasive animals and plants, such as the rosy wolfsnail (Euglandina rosea) and house rats (Rattus rattus). The rosy wolfsnail was introduced to Oʻahu in the 1950s to control the previously introduced giant African snail, but then also ate tree snails.

Also on the Seychelles, where more than 1,000 invertebrate species are endemic, numerous animals such as rats, pigs, cattle or chickens and also plants such as the cinnamon tree, which partially destroyed the native flora and fauna, arrived with humans. Since the end of the 19th century, at least five harvestman species have become extinct on the Seychelles, including Centrobunus braueri.

The Crayfish Pacifastacus nigrescens became extinct after the signal crayfish, along with crayfish plague pathogens, a fatal fungal disease in crayfish, reached California. Today, the signal crayfish can be found as a neozoon in most European countries. It poses a major threat to the three native crayfish species of Central Europe.

When the host animals of parasites die out

The extinction of an animal or plant species can trigger a chain reaction in which at least one other species also disappears. This is especially the case with parasites, which belong to the invertebrates and are closely associated with a host. If the host dies out, the parasite is also lost. For example, with the passenger pigeon from North America, the passenger pigeon mite also became extinct in 1914. A similar fate befell the nasal mite Halarachne americana, which exclusively colonized the airways of the Caribbean monk seal, which became extinct around 1952. Other examples are the feather mite Chiasmalges carolinensis, which lived parasitically on the feathers of the Carolina parakeet, or the louse Rallicola extinctus, which specialized on the huia as a host.

In the case of some less researched invertebrate species, only speculations can be made as to why they became extinct. These include, for example, the eyeless cave scorpion Akrav israchanani, which probably only occurred in two cave systems in Israel. The extinction of the land snail species Plegma duponti and Tropidophora carinata native to Mauritius in the 19th century also remains unclear.

Detailed pages are available for the following invertebrate animals:

• Passenger pigeon mite
• Yellow-tipped Oahu tree snail