Megadictyon

Megadictyon Temporal range:
Reconstruction of Megadictyon cf. haikouensis
Scientific classification
Kingdom:	Animalia
Clade:	Panarthropoda
Phylum:	†Lobopodia
Class:	†Xenusia
Order:	†Siberiida
Family:	†Siberiidae
Genus:	†Megadictyon Luo & Hu, 1999
Species:	†M. haikouensis
Binomial name
†Megadictyon haikouensis Luo & Hu, 1999

Megadictyon is a genus of Cambrian lobopodian known from the Chengjiang biota of China. It closely resembles Jianshanopodia and Siberion, with which it has often been placed in the family Siberiidae. The name of the genus is occasionally mis-spelt as Magadictyon.

Description

Megadictyon is a large lobopodian, with a body length (excluding appendages) possibly up to 20 centimetres (7.9 in) in total. The head has a pair of robust frontal appendages associated with rows of spines and terminal claws. Located on the underside of the head is a radiodont-like mouthpart formed by multiple layers of plates and tooth-like structures. The trunk is wide and annulated, with a pair of well-developed lobopodous limbs on each body segment. Only 8 segment/limb pairs are countable in the incomplete fossil materials which are lacking the posterior region, so it may have had more (possibly up to 11 to 13) in nature. It also has pairs of digestive glands similar to those of basal arthropods.

Taxonomy and phylogeny

Megadictyon has often been placed in the family Siberiidae along with Jianshanopodia and Siberion, which in turn are thought to represent among the closest relatives of arthropods among lobopodians.

Phylogeny of Panarthropoda and lobopodians after Knetcht et al. 2025:

	†Diania
	†Lenisambulatrix †Paucipodia †Thanahita †Eoconchariidae †Microdictyon †Fusuchoncharium †Quadratapora †Xenusion †Onychodictyon †Strictocorniculum †Rhombocorniculum †Orstenotubulus †Carbotubulus †Hallucigenia fortis †Hallucigenia sparsa †Hallucigenia hongmeia †Cardiodictyon Tardigrada †Luolishaniida †Ovatiovermis †Facivermis †Luolishania †Collinsovermidae †Acincocricus †Collinsovermis †Collinsium †Entothyreos †Aysheaiidae †Aysheaia †Hadranax †Palaeocampa Antennopoda †Antennacanthopodia Onychophora (velvet worms) †Siberiidae †Siberion †Megadictyon †Jianshanopodia †Pambdelurion †Kerygmachelidae †Opabiniidae †Radiodonta (e.g. Anomalocaris) Deuteropoda (modern arthropods)

Cladogram after McCall 2023:

Total group Euarthropoda	†Siberiidae †Siberion †Megadictyon †Jianshanopodia †Kerygmachelidae †Utahnax †Kerygmachela † Mobulavermis †Omnidens †Pambdelurion †Opabiniidae †Caryosyntrips †Radiodonta (e.g. Anomalocaris) Deuteropoda (modern arthropods)