Arenicolidae (Annelida) in Norwegian waters: species occurrence, bathymetric distribution and identification of juvenile specimens

Abstract

The two species of Arenicolidae, Arenicola marina and Arenicolides ecaudata, are common along the Norwegian coast. Juveniles and anterior fragments are often encountered when grab sampling, making traditional morphological characteristics insufficient for species identification. This study examined the robustness of the characteristics and development of branchiae in juvenile specimens of Arenicolides ecaudata (n = 109) and Arenicola (n = 44) (A. marina and Arenicola sp.) and additional specimens to assess geographic and bathymetric distribution. Neuropodia were discovered to be efficient in distinguishing the species. Branchiae of A. ecaudata appear when specimens measure between 7–13 mm, while in A. marina they appear in specimens measuring between 3–5 mm. The ring formula in anterior chaetigers is a key characteristic in differentiating between Arenicola species. This characteristic alone is insufficient for reliable species identifications, as study findings corroborated error rates in identification based on the ring formula. The bathymetric range of both species has increased considerably. Arenicola marina was documented at 194 m depth and A. ecaudata at 387 m depth. DNA barcodes with the cytochrome c oxidase subunit I (COI) gene were produced for three specimens of Arenicolides ecaudata, representing the first publicly available COI barcode sequences for this species. Five specimens of Arenicola marina, with similar sequences to specimens from other north-eastern Atlantic localities were also barcoded in BOLDsystems.