Abstract
Arrow worms (Phylum Chaetognatha) are abundant planktonic organisms and important predators in many food webs; yet, the classification and evolutionary relationships among chaetognath species remain poorly understood. A seemingly simple body plan is underlain by subtle variation in morphological details, obscuring the affinities of species within the phylum. Many species achieve near global distributions, spanning the same latitudinal bands in all ocean basins, while others present disjunct ranges, in some cases with the same species apparently found at both poles. To better understand how these complex evolutionary and geographic variables are reflected in the species makeup of chaetognaths, we analyze DNA barcodes of the mitochondrial cytochrome oxidase c subunit I (COI) gene, from 52 specimens of 14 species of chaetognaths collected mainly from the Atlantic Ocean. Barcoding analysis was highly successful at discriminating described species of chaetognaths across the phylum, and revealed little geographical structure. This barcode analysis reveals hitherto unseen genetic variation among species of arrow worms, and provides insight into some species relationships of this enigmatic group.
Highlights
Arrow worms (Phylum Chaetognatha) comprise over 120 species, all of which inhabit marine environments and exhibit hermaphroditic reproduction
The only overlap between these distributions results from comparisons of Eukrohnia hamata and E. bathyantarctica (K2P distances of 0.06–0.08)
Barcode analysis of chaetognaths was extremely successful in diagnosing established species based on COI gene sequence, in that sequences clustered by species in all cases
Summary
Arrow worms (Phylum Chaetognatha) comprise over 120 species, all of which inhabit marine environments and exhibit hermaphroditic reproduction. There are fewer species in this phylum than in many others, chaetognaths can be numerically abundant in many pelagic environments [1], and their grasping hooks, rows of strong teeth, and transparent bodies make them excellent predators in many marine food webs. Chaetognaths appear to have a relatively simple, conserved body plan, with few complex internal structures. Variation in morphological characters—e.g. position of lateral fins, morphology of tail fins, organization of teeth and grasping hooks—is often a matter of degree rather than of sharp contrast, making classification difficult [3]. The seemingly simple morphology of arrow worms belies an underlying mix of features synapomorphic to chaetognaths and features shared with other phyla, complicating placement at even the most basic levels of metazoan organization
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
