Tbx1/10 function is required for gill slit formation in the amphioxus pharynx. The anterior portions of larvae at 36 hours post fertilization (hpf) are shown in lateral views (with anterior to the left). The 50-μm scale bar in (A) is applicable to the entire figure. Amphioxus larvae are shown that were injected before fertilization with either 1,000 μM control antisense morpholino oligonucleotide (MO) or with 1,000 μM Tbx1/10 MO. The assayed genes are amphioxus Pax1/9 (A), (A’), Six1/2 (B), (B’), Pax2/5/8 (C), (C’), Pitx (D), (D’), Cyp26-2 (E), (E’) and TR2/4 (F), (F’).