Figure 1.
An abbreviated phylogeny of the Nudipleura Clade within Opisthobranchia.
The Nudipleura clade consists of the monophyletic clades Nudibranchia and Pleurobranchomorpha. Within Nudibranchia is the clade Cladobranchia, which consists of Dendronotida and Aeolida. Nudibranchia also includes the clade Doridoidea. The genera studied here are in bold. Genera in green boxes are genera that include species that produce rhythmic, dorsal-ventral flexions, in turquoise boxes are genera that produce rhythmic, left-right flexions, and in red boxes have not been observed to produce rhythmic body flexions. Larger boxes indicate monophyletic clades.
Figure 2.
C2 characteristics in Tritonia diomedea.
A. C2Tri could be identified visually due to its characteristic white soma near the origin of cerebral nerve 1 (CeN1, white arrows). An asterisk (*) labels the statocyst. Only one cerebral-pleural ganglion is shown. B. Filling the C2Tri soma with Neurobiotin revealed a contralateral axon projection through the anterior cerebral-pedal commissure (not shown) and into the pedal commissure (PP2). The example is a representative image in which the outline of the brain and the axon projection were traced for ease of viewing. C. C2Tri (arrow) was filled with biocytin (left). It was immunoreactive for both FMRFamide (middle) and SCPB (right) as shown. D. Backfilling the pedal commissure with biocytin in Tritonia labeled 3–4 neurons near C2Tri (left). Only the cerebral-pleural ganglion contralateral to the backfilled nerve is shown. FMRFamide-like immunohistochemistry labeled C2Tri (middle). Combining FMRFamide-like immunoreactivity with the backfill revealed just one neuron, C2Tri, (right).
Figure 3.
C2 characteristics in Pleurobranchaea californica.
A. C2Pleur could be identified visually due to its characteristic white soma near the origin of cerebral nerve 1 (CeN1, white arrows). It was the more anterior-lateral of two white neurons near the origin of CeN1 (the more medial white neuron is not seen here). Only one cerebral-pleural ganglion is shown. B. Filling the C2Pleur soma with biocytin revealed a contralateral axon projection through the anterior cerebral-pedal commissure (aCPC) into the pedal commissure (PP2). The example is a representative image in which the outline of the brain and the axon projection were traced for ease of viewing. C. C2Pleur (arrow) was filled with biocytin (left). It was immunoreactive for both FMRFamide (middle) and SCPB (right) as shown. D. Backfilling the pedal commissure with biocytin labeled 3–4 neurons near C2Pleur (left). Only the cerebral-pleural ganglion contralateral to the backfilled nerve is shown. FMRFamide-like immunohistochemistry labeled C2Pleur (middle). Combining FMRFamide-like immunoreactivity with the backfill revealed just one neuron, C2Pleur (right).
Figure 4.
C2 characteristics in Melibe leonina.
A. Backfilling the pedal commissure with biocytin labeled 3–4 neurons near C2Mel (left). Only the cerebral-pleural ganglion contralateral to the backfilled nerve is shown. FMRFamide-like immunohistochemistry labeled C2Mel (middle). Combining FMRFamide-like immunoreactivity with the backfill revealed just one neuron, C2Mel (right). B. C2Mel could be identified visually due to its characteristic white soma near the origin of cerebral nerve 1 (CeN1, white arrows). An asterisk (*) labels the statocyst. Only one cerebral-pleural ganglion is shown. C. Filling the C2Mel soma with Neurobiotin revealed a branching contralateral axon projection through the anterior cerebral-pedal commissure (not shown) and into the pedal commissure (PP2). The example is a representative image in which the outline of the brain and the axon projection were traced for ease of viewing. D. C2Mel (arrow) was filled with biocytin (left). It was immunoreactive for both FMRFamide (middle) and SCPB (right) as shown.
Figure 5.
C2 characteristics in Hermissenda crassicornis.
A. Backfilling the pedal commissure with biocytin labeled 3–4 neurons near C2Herm (left). Only the cerebral-pleural ganglion contralateral to the backfilled nerve is shown. FMRFamide-like immunohistochemistry labeled C2Herm (middle). Combining FMRFamide-like immunoreactivity with the backfill revealed just one neuron, C2Herm (right). B. C2Herm could be identified visually due to its characteristic white soma (black arrow) near the origin of cerebral nerve 1 (CeN1, white arrows). Note the white cell just medial to C2Herm (orange arrow). An asterisk (*) labels the statocyst. Only one cerebral-pleural ganglion is shown. C. Filling the C2Herm soma with biocytin revealed a contralateral axon projection through the anterior cerebral-pedal commissure (not shown) and into the pedal commissure (PP2). The example is a representative image in which the outline of the brain and the axon projection were traced for ease of viewing. D. C2Herm (arrow) was filled with biocytin (left). It was immunoreactive for both FMRFamide (middle) and SCPB (right) as shown. The white cell just medial to C2Herm is immunoreactive for FMRFamide, but not SCPB (orange arrow).
Figure 6.
C2 characteristics in Flabellina iodinea.
A. C2Flab could be identified visually due to its characteristic white soma (black arrow) near the origin of cerebral nerve 1 (CeN1, white arrows). Note the white cell just posterior-medial to C2Flab (orange arrow). Only one cerebral-pleural ganglion is shown. B. Filling the C2Flab soma with biocytin revealed a contralateral axon projection through the anterior cerebral-pedal commissure (not shown) and into the pedal commissure (PP2). The example is a representative image in which the outline of the brain and the axon projection were traced for ease of viewing. C. C2Flab (arrow) was filled with biocytin (left). It was immunoreactive for both FMRFamide (middle) and SCPB (right) as shown. The white cell just medial to C2Herm is immunoreactive for FMRFamide, but not SCPB (orange arrow).