Nemertea

There are over 30 invertebrate phyla and one of those is the phylum Nemertea, named for the Greek sea goddess Nemertes. Nemerteans are almost exclusively marine and can be found from the shallow intertidal to the deep sea. They are known for their capacity to stretch like rubber bands and their lack of segmentation, features which give rise to their common name – the ribbon worms. They are sleek predators and use an eversible proboscis to subdue clams and mussels.

Nemerteans, like many other marine invertebrates, have a biphasic life-history consisting of adult and larval stages. Benthic adults of most nemertean species reproduce by broadcast spawning gametes (eggs and sperm) which are fertilized and develop in the water column as tiny larvae. These larvae are planktonic – meaning they live and drift in the water. They can spend weeks to months in the plankton before they settle into their benthic and adult existence. It is these larvae that connect populations of species, sometimes over great distances. As you can imagine, the differing adult and larval habitats can lead to dramatically dissimilar morphology between the two developmental stages.

Species are identified based on their original descriptions and identification guides. But these guides are usually based on adult morphology, which means that most marine invertebrate larvae (having dissimilar morphology) cannot be identified. With this in mind, we began to identify the larvae of nemertean species collected near the Oregon Institute of Marine Biology on the southern Oregon coast. This guide serves to connect adults and larvae of nemerteans such that a species can be identified during both phases of life history.

Nemertean Taxonomy

The soft-bodied nature of the Nemertea provides relatively few characters of adult morphology and variations within those few characters can be confusing. In many instances, we have found that a species by the same name in two different regions may not be the same species at all.  Cerebratulus marginatus, for example, is a NE Pacific species that was originally described in Italy and subsequently synonymized over large geographic distances. The species now exhibits an apparent world-wide distribution, but personal communication with a variety of nemertean experts suggest that many species currently exist under the same name (thus, we refer to the northeastern species as Cerebratulus cf. marginatus).

The limitations of nemertean taxonomy and underlying reference databases mean that the identifications in this key can only be extrapolated to other species based on location in addition to DNA sequence data. As such, all sequences used within this database are available in GenBank.