Trigonalidae (the spelling Trigonalyidae is incorrect under Article 29.5 of the ICZN,ICZN Code
29.5. Maintenance of current spellings. If a spelling of a family-group name was not formed in accordance with Article 29.3 but is in prevailing usage, that spelling is to be maintained, whether or not it is the original spelling and whether or not its derivation from the name of the type genus is in accordance with the grammatical procedures in Articles 29.3.1 and 29.3.2. also historically sometimes spelled Trigonaloidae, based on an unjustified emendation) is one of the more unusual families of hymenopteran

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...

s, of indeterminate affinity within the suborder

Apocrita Apocrita is a suborder of insects in the order Hymenoptera. It includes wasps, bees, and ants, and consists of many families. It contains the most advanced hymenopterans and is distinguished from Symphyta by the narrow "waist" ( petiole) formed ...

(though sometimes believed to be related to the Evanioidea), and presently placed in a unique superfamily, Trigonaloidea, and the only extant taxon in the superfamily. The other putative related taxon is the extinct family Maimetshidae, known from the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

period. Trigonalidae are divided into 2 subfamilies; Orthogonalinae and Trigonalinae. These wasps are extremely rare, but surprisingly diverse, with over 90 species in 16 genera, and are known from all parts of the world.Trigonalidae Website
/ref> It is possibly the sister group to all

Aculeata Aculeata is a subclade of Hymenoptera containing ants, bees, and stinging wasps. The name is a reference to the defining feature of the group, which is the modification of the ovipositor into a stinger. However, many members of the group canno ...

. What little is known about the biology of these insects indicates a remarkably improbable life history: in nearly all known species, females lay thousands of minute eggs, "clamping" them to the edges of, or injecting them inside leaves. The egg must then be consumed by a caterpillar. Once inside the caterpillar, the trigonalid egg either hatches and attacks any other parasitoid larvae (including its siblings) in the caterpillar, or it waits until the caterpillar is killed and fed to a

vespid The Vespidae are a large (nearly 5000 species), diverse, cosmopolitan family of wasps, including nearly all the known eusocial wasps (such as ''Polistes fuscatus'', ''Vespa orientalis'', and ''Vespula germanica'') and many solitary wasps. Each ...

larva, which it then attacks. If the caterpillar is neither attacked by another parasitoid nor fed to a vespid, the trigonalid larva fails to develop. Therefore, they are parasitoids or

hyperparasitoid A hyperparasite, also known as a metaparasite, is a parasite whose host, often an insect, is also a parasite, often specifically a parasitoid. Hyperparasites are found mainly among the wasp-waisted Apocrita within the Hymenoptera, and in two ...

s, but in a manner virtually unique among the insects, in that the eggs must be swallowed by a host, and even more unusual in that there may be an intermediate host. A few species are known exceptions, which directly parasitise

sawflies Sawflies are the insects of the suborder Symphyta within the order Hymenoptera, alongside ants, bees, and wasps. The common name comes from the saw-like appearance of the ovipositor, which the females use to cut into the plants where they lay ...

. The fossil record of the family is poor, and there are no confirmed members of the family prior to the Cenozoic, with the oldest being from the

Ypresian In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by the Eocene Lutetian Age. The Ypresian ...

Eocene Okanagan Highlands The Eocene Okanagan Highlands or Eocene Okanogan Highlands are a series of Early Eocene geological formations which span a transect of British Columbia, Canada, and Washington state, United States. Known for a highly diverse and detailed plant an ...

in western North America. A possible specimen is known from the mid-Cretaceous

Burmese amber Burmese amber, also known as Burmite or Kachin amber, is amber from the Hukawng Valley in northern Myanmar. The amber is dated to around 100 million years ago, during the latest Albian to earliest Cenomanian ages of the mid-Cretaceous period. The ...

of Myanmar, but this differs substantially from modern members of the family, and may belong to the

stem-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

Genera

* '' Afrigonalys'' * '' Bakeronymus'' * '' Bareogonalos'' * '' Ischnogonalos'' * '' Jezonogonalos'' * '' Lycogaster'' * '' Mimelogonalos'' * '' Nomadina'' * '' Orthogonalys'' * '' Pseudogonalos'' * '' Pseudonomadina'' * '' Seminota'' * '' Taeniogonalos'' * '' Teranishia'' * '' Trigonalys'' * '' Xanthogonalos''

Genera

Fossil taxa

References

Notes