FB2026_03 , released September 17, 2026
CV Term Report
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General Information
Term ocular segment ID (Ontology) FBbt:00000005 (Fly Anatomy)
Definition Head segment derived from the second embryonic segment (between the labral and antennal segments). In the larva, this segment includes Bolwig's organ.[ FlyBase:FBrf0055841 FlyBase:FBrf0075072 ]
CommentWhile classically this structure is not considered to be a segment, but rather to be the non-segmental acron - anterior to the first segment, this ontology follows Schmidt-Ott and colleagues (Schmidt-Ott et al., 1994, and Schmidt-Ott and Technau, 1992) in considering it to be the second segment (posterior to the labral segment in the segmenting embryo). This is based on relating gene expression in the early segmenting embryo to the effects of loss of function mutations of these genes on formation of larval head structures.
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Data ClassFieldDirect annotations
Alleles (FBal)PHENOTYPE_MANIFEST_IN
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 ocular segment (all annotations which use CV term, excluding "NOT" statements)
     ocular segment | germline clone
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  head segment
   |__procephalic segment
       |__ocular segment  351 rec.
           |__adult ocular segment
           |__embryonic ocular segment 24 rec.
           |__larval ocular segment 313 rec.
               |__Bolwig nerve 88 rec.
               |__embryonic/larval dorsal pouch(+) 36 rec.
               |__larval ocular segment sense organ(+) 222 rec.
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Is a procephalic segment
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Synonyms
  • "acron" RELATED
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UBERON:6000005