Mygalomorphae

Mygalomorphs, Orthognatha

Family Guides

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Mygalomorphae is one of three major lineages of living spiders, comprising over 3,000 across 32 . Members include tarantulas, trapdoor spiders, and Australian funnel-web spiders. They are characterized by downward-pointing , two pairs of book lungs, and often large body sizes with exceptional longevity—some individuals live 25 years or more. The group exhibits remarkable morphological conservatism across its global distribution.

Aphonopelma paloma by (c) Chris A. Hamilton, Brent E. Hendrixson, Jason E. Bond, some rights reserved (CC BY). Used under a CC-BY license.Aphonopelma anax by (c) Chris A. Hamilton, Brent E. Hendrixson, Jason E. Bond, some rights reserved (CC BY). Used under a CC-BY license.Atypus karschi by (c) Andy Deans, some rights reserved (CC BY), uploaded by Andy Deans. Used under a CC-BY license.

Pronunciation

How to pronounce Mygalomorphae: /ˌmɪɡəloʊˈmɔːrfiː/

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Identification

Distinguished from Araneomorphae by downward-pointing (not crossing) fangs, two pairs of book lungs (versus one), and lack of cribellum. Distinguished from Mesothelae by absence of external abdominal segmentation and reduced number. Differs from other spiders in combination of orthognath , book lung retention, and typically robust body form. Molecular often required for -level identification due to morphological conservatism and .

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Appearance

Heavy-bodied, stout-legged spiders with large, powerful and fangs. Most have eight arranged as one principal pair and three secondary pairs. Body sizes range from less than 1 mm to 10 cm body length with 28 cm leg span in Theraphosa blondi. reduced to two pairs in most . Lack abdominal segmentation. Many species possess urticating setae on the . Some have stridulatory apparatus with setae on .

Habitat

Primarily terrestrial and , occupying burrows or constructing sheet webs and trapdoor structures. Many create silk-lined burrows with soil-and-vegetation trapdoors. Found in diverse substrates including sand dunes, rocky highlands, and forest soils. Some build above-ground sheet webs approaching one meter in diameter. Limited arboreal representatives compared to Araneomorphae.

Distribution

All continents except Antarctica. Highest diversity in tropics and subtropics; extends into temperate regions including southern and western United States. Only 12 occur in Europe across six . Fossil record indicates worldwide distribution prior to Pangaean breakup. Notable restricted distributions include coastal dune endemics in California and highland 'campos rupestres' in Brazil.

Seasonality

Activity patterns vary by strategy. Many are sit-and-wait at burrow entrances year-round. Long developmental periods—some do not reach maturity until approximately six years of age. Extended longevity with documented cases exceeding 40 years. Mating seasons may be seasonally restricted in some species.

Diet

Powerful of large arthropods; some kill small mammals, birds, and reptiles. Prey captured by ambush from burrows or active pursuit depending on web architecture.

Life Cycle

Extended lifespan with slow development. Some require ~6 years to reach maturity. may live 25 years or more; one documented female trapdoor spider lived 43 years. Endoparasitic Acroceridae flies may remain in book lungs for up to 10 years before consuming the . Females generally longer-lived than males.

Behavior

Primarily sit-and-wait . Trapdoor spiders detect prey vibrations and spring from concealed burrows. Many . Some engage in stridulatory communication using leg and cheliceral structures. Urticating setae used defensively in some tarantulas. Docile temperament documented in Brachypelma species contributes to pet trade popularity.

Ecological Role

Significant in terrestrial . control of large arthropods and small vertebrates. Prey for specialized including Acroceridae flies. Burrowing activities contribute to soil dynamics.

Human Relevance

Australian funnel-web spiders ( Atrax) pose serious medical risk; most harmless despite formidable appearance. Tarantulas widely kept in international pet trade, including CITES-listed species. Silk studied for biomaterial applications—stronger than steel and more stretchy than Kevlar. Subject of conservation concern for narrow-range endemics (e.g., Cryptocteniza kawtak classified as 'Endangered Living Fossil').

Similar Taxa

  • AraneomorphaeModern spiders with crossing (araneognath) fangs, single pair of book lungs, cribellum in many groups, and typically shorter lifespans (~1 year)
  • MesothelaePrimitive spiders retaining external abdominal segmentation and at least four pairs of ; limited to East and Southeast Asia

More Details

Morphological Conservatism

Mygalomorphae exhibit extreme morphological conservatism attributed to under similar . This complicates and necessitates molecular approaches for phylogenetic resolution. Recent genomic studies using Ultra Conserved Elements (UCEs) and anchored hybrid enrichment have substantially revised familial classifications.

Taxonomic Revision

Classification underwent major revision in 2020 (Opatova et al.), establishing superfamilies Atypoidea and Avicularioidea. Five elevated to rank, three new families created, and generic compositions of Ctenizidae, Cyrtaucheniidae, Dipluridae, and Nemesiidae relimited. Historical 'Tuberculotae' and 'Fornicephalae' divisions replaced by molecularly-supported groupings.

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