Table 1.
Molluscan Larval and Adult Muscle Systems
| Polyplacophora | Neomeniomorpha | Chaetodermomorpha | Monoplacophora | Bivalvia | Gastropoda | Scaphopoda | Cephalopoda | ||
|---|---|---|---|---|---|---|---|---|---|
| Larva |
∗Enrolling muscle | + | + | lateral longitudinal muscle? | ? | – | – | – | NA |
| ∗Rectus muscle | + | + | ? | ? | – | – | – | NA | |
| ∗Ventrolateral muscle | + | + | lateral longitudinal muscle? | ? | – | – | – | NA | |
| ∗Ventromedian muscle | + | + | ? | ? | – | – | – | NA | |
| ∗Ring musculature (as element of body wall musculature) | + | + | + | ? | – | – | – | NA | |
| Transversal musculature | + | – | ? | ? | – | – | – | NA | |
| Prototroch muscle ring | + | + | + | ? | + | + | – | NA | |
| Number of sets of dorsoventral muscles | multiple | 7 | ? | ? | 3–8 (?) | 1 | 1–2 | NA | |
| Adult | Enrolling muscle | + | +/– | – | – | – | – | – | – |
| Rectus muscle | + | – | – | – | – | – | – | – | |
| Ring musculature (as element of body wall musculature) | – | + | + | – | – | – | – | – | |
| Transversal musculature | + | – | – | – | – | – | – | – | |
| Number of sets of dorsoventral muscles | 7→8 | multiple | multiple (anteriorly only) or missing | 8 | 3–8 | 1 | 1–2 | 1 | |
Asterisks indicate potential synapomorphies of [Polyplacophora + Neomeniomorpha] or the entire Aculifera. +, present; −, absent; NA, not applicable. Note that in polyplacophorans, seven shell plates are formed simultaneously at first; an eighth forms considerably later in development, after metamorphosis. Note also that cephalopods have direct development and therefore lack molluscan-specific larvae.