Antennulata

Antennulata is a proposed clade of arthropods that unites the Artiopoda (trilobites and their close relatives), Marrellomorpha, and Mandibulata (crustaceans, hexapods, and myriapods). The name Antennulata refers to the hypothesized shared presence of antennulae, or small anterior appendages, which are considered to be an ancestral feature for these groups.^[1]

Antennulata Temporal range: Cambrian–Recent PreꞒ Ꞓ O S D C P T J K Pg N
Fossil of Triarthrus eatoni, a trilobite
Cherax wagenknechtae, a crustacean mandibulate
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
(unranked):	†Antennulata
Subgroups
†Artiopoda †Marrellomorpha? Mandibulata

Taxonomic history

The concept of Antennulata emerged as an alternative to the Arachnomorpha hypothesis, which proposes that artiopods (including trilobites) and marrellomorphs are more closely related to Chelicerata than to mandibulates.^[2] This debate reflects broader questions about the evolutionary placement of extinct groups like trilobites and marrellomorphs, which have features shared with both mandibulates and chelicerates.^[3]

Morphological support

Support for Antennulata comes from morphological studies that emphasize the presence of antenniform appendages and similarities in head segmentation among these groups.^[1] For instance, mandibulates possess prominent antennules (first antennae) and trilobites show anterior appendages interpreted as homologous structures.^[4]

Competing hypotheses

While Antennulata has been proposed to link these groups, the Arachnomorpha hypothesis remains influential. Arachnomorpha suggests that trilobites and marrellomorphs share more derived features with chelicerates than with mandibulates.^[2] Molecular studies often favor Mandibulata as a robust clade but have produced mixed results for the placement of extinct groups like trilobites, which rely primarily on fossil morphology for phylogenetic placement.^[5]