Neoamphitrite undevigintipes, Choi & Kim & Yoon, 2020

Choi, Hyun Ki, Kim, Hana & Yoon, Seong Myeong, 2020, Neoamphitrite undevigintipes, a new terebellid species from South Korea (Annelida, Terebellida, Terebellidae), ZooKeys 943, pp. 41-51 : 41

Neoamphitrite undevigintipes sp. nov. Figures 1 , 2 , 3

Type locality.

South Korea, East Sea (Sea of Japan), 36°35'08.0"N, 130°08'19.7"E, 500-1000 m in depth.

Material examined.

Holotype: complete specimen (NIBRIV0000753905). Paratypes: one complete specimen (MABIKNA00156356); one complete specimen (MABIKNA00156357); one complete specimen (MABIKNA00156358); one complete specimen (MBIKINA00156359); one complete specimen (MABIKNA00156360). Non-type material: 16 specimens (all complete specimens). All materials examined were collected from the type locality, 13 April 2018 using the benthic trawl mounted on RV Tamgu 21 of National Institute of Fisheries Science (NIFS) from Korea.

Diagnosis.

Body with distinct thoracic and abdominal region. Tentacular lobe collar-like. Peristomium with fleshy ridge on ventral side. Upper lip distinct and undulate with free margin. Lower lip well developed, projecting forward. Buccal tentacles filiform with ventral groove. Lateral lappets present on segments 2-4, well developed on segments 2 and 3, reduced on segment 4. 12 ventral shields from segment 3. Branchiae dichotomous with distinct stalk, 3 pairs, and present on segments 2-4. Nephridial papillae small, oval on segments 3-15, located between noto- and neuropodia. Notopodia present on 19 chaetigers on segment 4. Notochaetae medially winged and distally serrated. Neuropodia beginning at segment 5. Uncini avicular, short-handled, arranged in single row on segments 5-10, in double rows of beak to beak arrangement from segments 11-22, and in single row on all abdominal segments. Dental formula MF: 4-5: 5-6: 7-8. Pygidium reduced with 10 papillae.

Description.

Holotype: complete, 11.0 cm long, 1.5 cm wide at segments 10, and with approximately 74 segments. Body uniformly light beige in alcohol, without pigmentation pattern, and consist of thorax with 19 chaetigers and abdomen; anterior thoracic segments compact until about 13 and then segments slightly narrower and longer than 13 anterior segments (Figs 1 , 3A, B, E ). Tentacular lobe short and collar-like. Peristomium with fleshy ridge on ventral side, separated anteriorly from lower lip by groove. Upper lip distinct and undulate with free margin. Lower lip well-developed, projecting forward. Buccal tentacles filiform with ventral groove. Lateral lappets paired on segments 2-4, distinct thickness flaps, protruding forwards, and with weakly developed glandular margin; first and second lappets well-developed, but third lappets reduced in length, located on nearby base of notopodia. Branchiae paired on segments 2-4, dichotomous, with 3 tiers of branches and weakly annulated stalk distinct. Nephridial papillae small, oval, present on segments 3-15, and located between noto- and neuropodia; those with fused tube retracted into body on segments 6-8 and other with free tube distinctly projecting from the body. Ventral shields trapezoidal, broader than longer, present on segments 3-14; first shield on segment 3 with glandular margin and others with smooth margin; thereafter shields replaced by mid-ventral groove extending to pygidium (Figs 2A , 3A, B, E ). Notopodia short, rectangular, present on segments 4-22 (chaetigers 1-19); last 2 or 3 pairs becoming much shorter. Notochaetae slightly curved, medially winged and distally serrated, types of 2 lengths; chaetae on anterior row at least half as long as those on posterior row (Figs 2C , 3E-H ). Neuropodia beginning from segment 5 as low rectangular ridges, and with uncini arranged in single rows on segments 5-10 (chaetigers 2-7), uncini in double rows beak to beak arrangement on segments 11-22 (chaetigers 8-19), and in single row on all abdominal segments. Uncini avicular, short-handled with short triangular heel, distally pointed prow, minute dorsal button, and 5 rows of secondary teeth on main fang with subrostral guard. Dental formula MF: 4-5: 5-6: 7-8 (Figs 2B , 3C, D ). Pygidium reduced with encircling 10 papillae.

Etymology.

A combination of the Latin undeviginti and pes. This name means 'nineteen feet’, referring to the 19 pairs of notopodia on the thoracic segments.

Habitat.

This species is found on the soft bottom of deep waters (500-1000 m depth) and lives in a mud tube.

Remarks.

In Neoamphitrite taxonomy, the number of notopodia is a key character for the identification of species ( Hutchings and Glasby 1988; Hilbig 2000; Londoño-Mesa and Carrera-Parra 2005; Reuscher et al. 2012). Neoamphitrite undevigintipes sp. nov. has 19 pairs of notopodia on the thoracic segments regardless of body size and number of segments. In this respect, the new species is most similar to Neoamphitrite groenlandica (Malmgren, 1866), which was originally described from the Atlantic Ocean and also has 19 pairs of notopodia (Malmgren 1866; Hessle 1917; Fauvel 1927). However, the new species is clearly differentiated from N. groenlandica by two characteristic features. The uncini in the first abdominal chaetiger are arranged in a single row in N. undevigintipes sp. nov., but in double rows in N. groenlandica , and the new species has 12 ventral shields, but N. groenlandica has 14 (Malmgren 1866; Hessle 1917; Fauvel 1927).

In East Asia, three Neoamphitrite species, N. edwardsi (Quatrefages, 1865), N. ramosissima (Marenzeller, 1884), and N. vigintipes (Grube, 1870) from Japan, have been recorded ( Hessle 1917; Imajima and Hartman 1964; Paik 1989). Neoamphitrite undevigintipes sp. nov. shows several differences from these species as follows: notopodia of N. undevigintipes sp. nov. are present on 19 chaetigers, compared to 17 in N. ramosissima and N. edwardsi . Neoamphitrite undevigintipes sp. nov. has uncini arranged in a single row in all abdominal chaetigers, while N. vigintipes has the uncini arranged in double rows in abdominal chaetigers except for some final chaetigers. The new species has 13 pairs of nephridial papillae, whereas six, nine, and 12 pairs are present in N. ramosissima , N. edwardsi , and N. vigintipes , respectively ( Hessle 1917; Imajima and Hartman 1964; Paik 1989).

Hessle (1917) suggested that Neoamphitrite species are distinguished from Amphitrite species by having nephridial papillae with free tubes distinctly projecting from the body rather than fused tubes retracted into the body. However, in several specimens of N. undevigintipes sp. nov., the nephridial papillae have fused tubes in two or three of all nephridial papillae pairs. Hutchings and Glasby (1988) mentioned that the form of nephridial papillae is difficult to use as a generic diagnostic feature because it can be variable according to the state of specimens. This character was overlooked in diagnoses of the terebellid genera ( Fauvel 1927; Caullery 1944; Fauchald 1977; Hilbig 2000; Hutchings and Glasby 1988; Londoño-Mesa and Carrera-Parra 2005; Reuscher et al. 2012). In this respect, we think that the form of nephridial papillae is not yet a useful diagnostic character and that its taxonomic value should be re-examined in detail using as many species as possible. We provide a key to the species presently regarded as members of Neoamphitrite .

Genetic information.

In this study, partial COI sequences, each measuring 658 bp, were obtained from three specimens for genetic analysis of Neoamphitrite undevigintipes sp. nov. They are deposited in the GenBank under accession numbers MN306311 to MN306313. All COI sequences obtained were identical. Using data available from the GenBank ( Carr et al. 2011; Siddall et al. 2011; Telfer and Dewaard 2017), we genetically compared the new species with two Neoamphitrite species, N. figulus (Dalyell, 1853) and N. robusta (Johnson, 1901), as well as six species belonging to the other terebelline genera: Amphitrite cirrata Müller, 1776, Nicolea zostericola Örsted, 1844, Pista maculata (Dalyell, 1853), Pista wui Safronova, 1988, Loimia arborea Moore, 1903, and Loimia medusa (Savigny, 1822). Thelepus cincinnatus (Fabricius, 1780) was used as the outgroup. GenBank accession numbers are represented in Table 1 . Inter-specific genetic distances between the new species and two Neoamphitrite species, as measured by Kimura-2-parameter model, were distinct and ranged from 9.2 to 13.7%. The genetic distances between the new species and the six species in other genera ranged from 21.8 to 29.9%. In the maximum likelihood (ML) tree based on these genetic data (Fig. 4 ), all terebellid species showed specific validity. The new species was contained in a clade with N. figulus and N. robusta . At the generic level, the Neoamphitrite clade, including the new species, was closely related to A. cirrata , agreeing with the taxonomic view that Neoamphitrite and Amphitrite share many morphological features except for differences in the morphology of branchiae (Hessel 1917; Fauvel 1927; Hutchings and Glasby 1988; Reuscher et al. 2012). However, Neoamphitrite was monophyletic and clearly distinguishable from A. cirrata in the ML tree, supporting the known morphological differences between two genera (Hessel 1917; Fauvel 1927; Hutchings and Glasby 1988; Reuscher et al. 2012). Despite our results, further genetic studies with additional data and including more species of Neoamphitrite and Amphitrite are needed to confirm the phylogenetic relationship between the two genera.

Figures

Figure 1. Neoamphitrite undevigintipes sp. nov., paratype (MABIKNA 00156356), lateral view. Scale bar: 1.0 cm.

Figure 2. Neoamphitrite undevigintipes sp. nov. A holotype (NIBRIV 0000753905) B, C paratype (MBIKINA 00156359). A Anterior end, lateral view B uncinus C notochaeta. Scale bars: 1.0 mm (A), 0.05 mm (B), 0.1 mm (C). Abbreviations: fr - nephridial papillae with free tube, fu - nephridial papillae with fused tube.

Figure 3. Neoamphitrite undevigintipes sp. nov. A paratype (MABIKNA 00156357) B paratype (MABIKNA 00156358) C (MBIKINA 00156359) D-H (MABIKNA 00156360). A Anterior end, lateral view B anterior end, ventral view C notopodial uncinus, lateral view D uncini arranged in double rows E thorax with 19 notopodia F last thoracic segment with uncini arranged in double rows and first abdominal segment with uncini arranged in single row G notochaetae H distal region of notochaetae. Scale bars: 1.0 mm (A, B), 0.025 mm (C, D), 5.0 mm (E), 0.5 mm (F), 0.1 mm (G), 0.025 mm (H). Abbreviations: fr - nephridial papillae with free tube, fu - nephridial papillae with fused tube.

Figure 4. Maximum likelihood (ML) tree showing phylogenetic relationship based on COI sequences of three Neoamphitrite species with seven related species assigned to other genera and a outgroup species. Numbers above the branch indicate ML bootstrap values from 1000 replication.