Phylogenetically, all pilidiophorans are expected to produce a pilidium larva (Thollesson and Norenburg, 2003), but the specific larval morphology can be highly variable (e.g., see Leuckart and Pagenstecher, 1858; Fewkes, 1883; Dawydoff, 1940; Cantell, 1966a, b; Norenburg and Strieker.
As in a typical pilidium, the primary larval ciliated band spans the lobes and lappets (Fig.
alaskensis (Maslakova, 2010a; von Dassow et al., 2013), with prominent radial muscles in the lobes and lappets, a thick muscle strand along the primary ciliated band, and muscle strands that cross the lappets at their base, allowing the pilidium to constrict the lappets (Fig.
"red" larvae also resembles that of a typical pilidium. The first two pairs of juvenile rudiments, the cephalic discs and trunk discs, are present by 15 d PF (Fig.
Although the larval body is shaped like a typical (hat-like) pilidium, the larvae of M.
This is important, because it means that the presence of juvenile eyes in a wild-caught pilidium larva does not necessarily indicate that the species possesses eyes as an adult.
The devouring of the larval tissues during the metamorphosis of pilidium larvae (Nemertini).
Nemertean development is traditionally categorized into "indirect," meaning development via a long-lived plank-totrophie pilidium larva, as in most pilidiophoran species for which development is known (e.g., Coe, 1899, 1943; Dawydoff.
When palaeonemerteans and hoplonemerteans are lumped together as "'direct developers," what is meant by this is simply that these groups lack the pilidium larva and its drastic metamorphosis, but developmental modes in these groups are neither uniform nor, necessarily, direct in the usual sense.
Determination of the cell lineage by using intracellular markers and comparison with the pilidiophoran species that have lost the pilidium secondarily--for example Poseidon viridis, Poseidon ruber, and Micrura akkeshiensis--will likely help to clarify the direction of evolutionary transition between the hoplonemertean and pilidiophoran larval epidermis.
Morphology, development and biology of the pilidium larvae (Nemertinil from the Swedish west coast.