Developmental diversity in free-living flatworms

Table 1 Comparison of the embryonic development of the main free-living flatworms

				Neoophora
								Adiaphanida
	Catenulida	Macrostomorpha	Polycladida	Lecithoepitheliata	Proseriata	Bothrioplanida	Rhabdocoela	Fecampiida	Prolecithophora	Tricladida
Egg	Entolecithal	Entolecithal	Entolecithal	Ectolecithal	Ectolecithal	Ectolecithal	Ectolecithal	Ectolecithal	Ectolecithal	Ectolecithal
Cleavage	Spiral (early)	Spiral (early)	Spiral	Spiral	Spiral (early)	Disperse	Irregular	Irregular	Disperse	Disperse
Specification^a	?	Emb. blast.	Mosaic	Emb. blast.	Emb. blast.	Emb. blast.	Emb. blast.	Emb. blast.	Emb. blast.	Emb. blast.
Mesentoblast	?	-	4d²	4d	-	?	-	?	-	-
Gastrulation	?	Inverse epiboly (kind of)	Epiboly	Epiboly	Modified epiboly	-	Epiboly (kind of)	"Invagination"	Inverse epiboly (some)	-
Hull membrane^b	?	Yes	-	Yes	Yes	Yes	Variable	-	Variable	Yes
Blastopore	?	?	Yes	Yes	Yes	-	-	-	-	-
Emb. Pharynx^c	?	-	-	-	-	-	-	-	-	Yes
AP axis^d	?	An-Veg	modified An-Veg	?	?	?	?	?	?	?
DV axis^e	?	?	AB quad. ventral, CD quad. dorsal	An-Veg	An-Veg	?	?	?	?	?
LR axis^f	?	?	BC quad. right, AD quad. left	?	?	?	?	?	?	?
Larva	Juvenile described as "larva"	-	Yes	-	-	-	-	Juvenile described as "larva"	-	Embryo described as "larva"

^aCell-type specification: in the Polycladida development is determinative. In the rest of the groups, organs develop from an embryonic blastema (Emb. blast.)
^bOrigin of hull cells: Macrostomorpha, blastomeres 2A-2D; Lecithoepitheliata and some Proseriata, animal micromeres; some Rhabdocoela and Bothrioplana, unspecified micromeres or blastomeres; Tricladida, some Prolecithophora, some Rhabdocoela, some Proseriata, yolk cells
^cEmbryonic pharynx
^{d, e, f}Anteroposterior, dorsoventral and left-right axis, respectively. An-Veg means animal-vegetal axis and quad. means quadrant

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