Wild-caught larvae of Paranemertes californica collected in February (left, middle) and June (right) 2013. Note size variation between seemingly younger (left) and older individuals (right, middle). Scale bars 100 µm.
Paranemertes californica
Sequence Data: 16S, COI
Observed in Coos Bay: Jan-Mar, May-June
The larvae of Paranemertes californica range in size dramatically (above). Although hoplonemerteans are supposedly non-feeding and lack the ability to feed, recent evidence based on DNA sequence data of gut contents and variations in conspecific larval size, suggests that some species may be feeding (Maslakova and Hiebert 2014). Advanced P. californica larvae have three pairs of eyes, distinct cerebral ganglia and a distinct head shape with a constriction at the posterior most pair of eyes immediately anterior to the cerebral organs. Larger larvae also have long coiled proboscis (which is everted readily, below middle) and a stylet can be observed. They also tend to contort into a variety of positions such that their paired eyes are often difficult to separate.
Larva of Paranemertes californica collected in February 2013. Note the three pairs of eyes and coiled proboscis (left) which is everted (middle) readily and is equipped with a nail-like stylet (right). Scale bars 100 µm.
Identity uncertain
As mentioned in our methods section, matching larvae to adults using DNA sequence data is relatively straightforward because the sequences usually match so closely. In fact, unless mentioned otherwise all larvae identified with sequence data on this website show sequence divergences of <1% from their corresponding adults (for both 16S and COI gene regions). The larvae identified here as Paranemertes californica show little divergence for the 16S gene region (0.1%, below). For the COI gene region, however, there are two distinct groups where divergences between them is 5.9% (below). Although, this is below the average interspecific sequence divergence for congeneric nemertean species (3-5% for 16S, Mahon et al. 2010; Meyer and Paulay 2005; Hiebert and Maslakova unpublished and 19.6% for COI, Kvist et al. 2014), it remains higher than we typically see for species level larval identification. These larvae are commonly encountered in plankton samples, however whether they are the larvae of P. californica or another closely related species remains to be seen.
Neighbor-joining trees for the COI (left) and 16S (right) gene regions where the same individuals represented in both trees are connected with dashed lines.