Cirratulidae, Ryckholt, 1851

Blake, James A., 2023, New Species of Cirratulidae (Annelida) from Continental Slope and Abyssal Depths off Eastern Australia, Records of the Australian Museum (Rec. Aust. Mus.) 75 (3), pp. 249-270 : 266-269

Species of Cirratulidae from abyssal depths

In the present study “abyssal” depths are regarded as beginning at about 3000 m and continuing to the deepest parts of the abyssal plain. Historically, the deep-sea fauna was considered to be impoverished. This idea was largely based on the difficulty of obtaining samples and the paucity of most of the more typical benthic fauna known from studies of shallow-water habitats. Although the Challenger Expedition (1872–1876) and later Galathea Expedition (1950–1952) demonstrated that life was found in the deepest parts of the ocean, it was generally considered to be species-poor. The use of coarse mesh trawls and dredges used in those early expeditions were unable to adequately collect the more numerous smaller benthos known to occur in shallow waters.

Based largely on deep-water surveys during the 1960s, in which more quantitative samplers such as epibenthic sleds and fine-mesh sieves to separate the fauna from the sediments, benthic invertebrates from bathyal, slope, and abyssal depths in the North Atlantic Ocean were found to be far more diverse than previously believed ( Sanders et al., 1965; Sanders & Hessler, 1969). Hartman (1965) and Hartman & Fauchald (1971) documented polychaetes from Sanders’ North Atlantic surveys and collectively described more than 100 new species and several new genera. The introduction of quantitative box cores, multicores, and mega cores in subsequent years has yielded many more benthic invertebrate species and resulted in further estimates of high species richness in deep-sea sediments (e.g., Grassle & Maciolek, 1992).

The first compendium of abyssal polychaetes was by Hartman (1971) who listed 12 species of Cirratulidae in three genera. The majority of the cirratulid records she cited, however, were either not well documented or carried names that were derived from taxa, such as Chaetozone setosa Malmgren, 1867 that at the time were considered to be cosmopolitan in distribution. As a result, only two of the species listed by Hartman (1971) from 3000 m or greater are currently listed as valid in WoRMS. Recent studies of deep-water cirratulids by Blake (2006, 2016, 2018, 2019, 2022; this study; Doner & Blake, 2006) allow for a more comprehensive summary of cirratulids from 3000 m and greater.

Out of approximately 300 known species of Cirratulidae , about 220 belong to the bitentaculate genera and include an increasing number of deep-water taxa as materials from various expeditions and monitoring surveys are analyzed. Table 1 includes a list of 37 species of Cirratulidae recently described, or documented from depths of 3000 m or greater.

These 37 abyssal cirratulids are all from relatively few geographic areas: eastern Pacific off California (7), Peru-Chile Trench (3), Equatorial Pacific Ocean (12), eastern Australia (6), Antarctic seas (5), Western North Atlantic Ocean (3), and the Mozambique Channel, Indian Ocean (1). There are large areas in the Northern Pacific Ocean, northeast Atlantic Ocean, South Atlantic Oceans, and Indian Oceans where no abyssal cirratulids have been reported. In addition, despite the fact that 12 new cirratulid species were described from the abyssal plain of the Clarion-Clipperton zone in the Equatorial Pacific Ocean by Blake (2016, 2019); this area represents only a small fraction of the immense Pacific Basin. In keeping with the number of known species globally, the genera Aphelochaeta (12 species) and Chaetozone (15 species) are the best represented among the abyssal cirratulids that have been described to date. It is noteworthy that of the 37 species listed in Table 1 , 34 have been described in the past 15 years, emphasizing the increasing interest in deep-sea exploration.

ACKNOWLEDGEMENTS. The author thanks the CSIRO Marine National Facility (MNF) for its support in the form of sea time on RV Investigator , support personnel, scientific equipment, and data management. All data and samples acquired on the voyage are made publicly available in accordance with MNF Policy. I also thank all the scientific staff and crew who participated in the voyages. Project funding was provided by the Marine Biodiversity Hub, supported through the Australian Government’s National Environmental Science Program (NESP). Drs Laetitia M. Gunton and Elena Kupriyanova of the Australian Museum, Sydney are thanked for providing these interesting collections for study. Dr Stephen Keable, Collection Manager at the Australian Museum organized the specimen shipment and provided catalogue numbers. Mr Adam Baldinger, Invertebrate Collection Manager of the Museum of Comparative Zoology, Harvard received the samples for my study and returned them after the project was completed. A draft of this paper was reviewed and edited by Dr Nancy Maciolek, whose effort is greatly appreciated. Insightful comments by Dr Wagner Magalhães and an anonymous reviewer improved the final version of the manuscript.