The larvae of Paranemertes peregrina (left) and Zygonemertes sp. 1 (right) were collected in February 2013. Scale bars 100 µm. — The larvae of *Paranemertes peregrina* (left) and *Zygonemertes* sp. 1 (right) were collected in February 2013. Scale bars 100 µm.

Paranemertes peregrina & Zygonemertes sp. 1

The larvae of Paranemertes peregrina and a local Zygonemertes sp. 1 are difficult to differentiate. They are 'classic' hoplonemertean larvae with several pairs of eyes (usually three), a conspicuous apical tuft, a posterior cirrus and distinct cerebral ganglia. Sometimes, the larvae of these two species can be recognized by the color of their eyes: P. peregrina with reddish eyes and Zygognemertes sp. 1 with black eyes, but this is not completely consistent. Instead, these species can be differentiated by their early embryos both of which are common in plankton samples in winter months.

Months collected:  Jan–Feb — Months collected: Jan–Feb

Paranemertes peregrina

Sequence Data: 16S, COI

The development of Paranemertes peregrina has been described (Maslakova and von Döhren 2009). The embryos of P. peregrina are 250 µm in size and surrounded by a large egg chorion (especially when compared to the egg chorion of Zygonemertes sp. 1, below). After 2–3 days, a ciliated larva, with apical tuft begins swimming and at six days the larva with three pairs of eyes develops. The larvae are lecithotrophic and planktonic for 3–8 weeks (Roe 1976; Maslakova and von Döhren 2009), but their embryos are very common in the plankton.

Months collected:  Dec–April — Months collected: Dec–April

Zygonemertes sp. 1

Sequence Data: 16S, COI

The embryos of Zygonemertes sp. 1, on the other hand, are 180 µm in diameter and surrounded by a smaller chorion than P. peregrina. Ciliated larvae with an apical tuft begin swimming after two days and develop into larva with three pairs of eyes at five days.