Metamorphosis in Craniiformea revisited: Novocrania anomala shows delayed development of the ventral valve

Hox gene expression in postmetamorphic juveniles of the brachiopod Terebratalia transversa

“…One can therefore speculate, that as larval and adult body plans in Linguliformea are continuous, their patterning by Hox genes should be similar as is a case in T. transversa . On the other hand, there are two competing hypotheses about nature of the rearrangement of the larval body plan during metamorphosis of craniiformean brachiopods [62, 82, 83, 87, 88]. The main controversy regards whether N. anomala larva, which lacks the distinct pedicle lobe, attaches to the substrate with its dorso-posterior side [82] or with the posterior tip of the posterior lobe [83].…”

Brachiopoda

“…12.5 ). Altenburger et al ( 2013 ) disagreed with these interpretations based on the following reasons: (i) Initial larval attachment to the substrate was achieved by the posterior tip of the mantle (posterior) lobe similar to other rhynchonellid larvae (Stricker and Reed 1985a ), and (ii) the ventral attachment area included a cuticle but neither mantle tissue nor a ventral valve until 17 days postmetamorphosis. Further implications of Nielsen's interpretations pertain to the features of the ancestral brachiopod in which both the dorsal and ventral valves at metamorphosis are derived from different anterior and posterior regions of the larval dorsal epithelium (Nielsen 1991 ).…”

“…Since adult craniiform brachiopods lack a pedicle and cement directly to the substrate at metamorphosis, the posterior larval lobe that bears chaetae has typically been interpreted as the mantle lobe (Nielsen 1991 ). However, this interpretation has been challenged, as cell types of both the mantle and perhaps the pedicle lobes may be present in the posterior larval lobe of Novocrania (Altenburger et al 2013 ). Ciliation on the apical lobe is uniform and simple (Nielsen 1991 ), and although a pair of anterolateral red-pigmented spots has been observed on the apical lobe, it is not known if these structures are ocelli.…”

Evolutionary Developmental Biology of Invertebrates 2

“…According to Nielsen ( 1991 ), competent larvae use ventral musculature in the mantle (posterior) lobe to bend the larval body. Altenburger et al ( 2013 ) disagreed with these interpretations based on the following reasons: (i) Initial larval attachment to the substrate was achieved by the posterior tip of the mantle (posterior) lobe similar to other rhynchonellid larvae (Stricker and Reed 1985a ), and (ii) the ventral attachment area included a cuticle but neither mantle tissue nor a ventral valve until 17 days postmetamorphosis. Over time the larval body fl attens and the dorsal shell fi eld expands, pushing the chaetal bundles to the periphery of the juvenile body (see Fig.…”

“…Late-stage larvae have pigmented ocelli on the dorsal side of the apical lobe and vesicular bodies that border the posterior margin of the apical lobe. However, this interpretation has been challenged, as cell types of both the mantle and perhaps the pedicle lobes may be present in the posterior larval lobe of Novocrania (Altenburger et al 2013 ). Other features of the mantle lobe are the paired dorsal and medial chaetal sacs and a mid-ventral band of cilia.…”