Prionospio expansa, Lee & Lee & Min, 2023

Lee, Geon Hyeok, Lee, Ha-Eun & Min, Gi-Sik, 2023, Morphology and phylogeny of a new polychaete, Prionospio expansa (Annelida: Spionidae) from the intertidal zone of the Yellow Sea, Korea, European Journal of Taxonomy 885, pp. 86-98 : 89-94

Prionospio expansa sp. nov.

urn:lsid:zoobank.org:act:FFB09C6C-8B69-4FD3-A49B-EFCC348F3B14

Figs 2–4

Diagnostic features

Prostomium with orangish-brown pigmentations, anteriormost body conspicuously expended ( Fig. 3C– D ), four pairs of short, apinnate, and cirriform branchiae, dorsal crests and ventral flaps absent.

Etymology

The specific epithet ‘ expansa’ refers to the conspicuously expanded body in the anteriomost chaetigers of the new species.

Material examined

Holotype KOREA • 1 complete spec. with palps; Yellow Sea, Yeongjongdo Is., Eurwangni Beach ; 37.4472 ° N, 126.3705 ° E; 1 Apr. 2022; Geon Hyeok Lee leg.; intertidal, silty sand; NIBRIV0000900991 .

Paratypes KOREA • 1 complete spec.; Yellow Sea, Jaeun Is.; 34.9200 ° N, 126.0572 ° E; 24 Sep. 2021; Geon Hyeok Lee leg.; low intertidal, muddy sand; NIBRIV0000900998 • 4 af; Yellow Sea, Deokjeok Is.; 37.2065 ° N, 126.1743 ° E; 24 Oct. 2021; Geon Hyeok Lee leg.; low intertidal, muddy sand NIBRIV0000900999 • 10 complete specs, 9 af, 10 mf, 7 pf; same collection data as for holotype; 1 Apr. 2022; Geon Hyeok Lee leg.; NIBRIV0000901890–1891 (2 complete specs), NIBRIV0000900992–0993 (2 complete specs), other for NIBRIV0000901000 • 1 complete spec.; Yellow Sea, Deokjeok Is.; 37.2165 ° N, 126.1120 ° E; 16 Apr. 2022; Geon Hyeok Lee leg.; low intertidal, muddy sand; NIBRIV0000901001 • 7 complete specs, 21 af, 5 mf; same collection data as for holotype; 2 May. 2022; NIBRIV0000901002 • 1 af; same collection data as for holotype; 15 Jan. 2021; GenBank COI gene OQ672519 , GenBank 16S gene OQ685963 , GenBank 18S gene OQ685953 ; NIBRIV0000900994 • 3 complete specs; same collection data as for holotype; 1 Apr. 2022; GenBank COI gene OQ672520 – 2522 , GenBank 16S gene OQ685964 – 5966 , GenBank 18S gene OQ685954 – 5956 ; NIBRIV0000900995–0997 .

Description

Holotype complete with 90 chaetigers, about 0.41 mm wide at chaetiger 4 and about 14.2 mm long. Paratypes complete with 61–105 chaetigers, up to 0.51 mm wide at chaetiger 4 and about up to 15.5 mm long. Body conspicuously expanded dorsoventrally in chaetigers 2–6 ( Fig. 3C–D ), cylindrical afterwards, tapered towards pygidium ( Fig. 4A ).

Prostomium subtriangular, with three small peaks on anterior margin ( Fig. 4E ), extending posteriorly to posterior end of chaetiger 1 as a distinct caruncle; two pairs of reddish and rounded to oval eyes arranged in trapezoid, anterolateral pair larger and wider apart than posterior pair ( Figs 2A , 3C–D). Peristomium reduced, fused to chaetiger 1, not forming lateral wings. Palps reaching up to about chaetiger 25 with longitudinal groove lined with fine cilia. Nuchal organs U-shaped, reaching posterior end of chaetiger 1, separated by caruncle ( Fig. 4C ). Transverse ciliated bands and intersegmental transverse ciliation indiscernible ( Fig. 4B–C ).

Chaetiger 1 moderately developed, with large, rounded notopodial postchaetal lamellae and small rounded neuropodial postchaetal lamellae; notopodial postchaetal lamellae similar in size to second notopodial postchaetal lamellae; only a few chaetae on both rami; prechaetal lamellae absent ( Fig. 4B ).

Notopodial postchaetal lamellae foliaceous on chaetigers 2‒5, becoming rounded in middle chaetigers, then subtriangular in posterior chaetigers; notopodial postchaetal lamellae largest in chaetigers 3 and 4, then abruptly decreasing in size posteriorly ( Fig. 4B–C ). Neuropodial postchaetal lamellae foliaceous on chaetiger 2, subrectangular on chaetiger 3, rounded from chaetiger 3; neuropodial postchaetal lamellae largest in chaetigers 2 and 3, then gradually decreasing in size posteriorly. Low and rounded prechaetal lamellae in both rami present in anterior chaetigers, but absent in middle and posterior chaetigers.

Anterior notochaetae all unilimbate capillaries, heavily granulated ( Figs 2F , 3H), arranged in three rows; from about chaetiger 16, notochaetae arranged in two rows, then becoming arranged in a bundle posteriorly; anterior neurochaetae unilimbate capillaries rather thin, heavily granulated, arranged in two rows; sheaths of capillaries most broad at first 6–7 chaetigers; granulation disappeared in posterior chaetigers. Hooded hooks in notopodia appearing from chaetigers 28–38 (usually 35–38), numbering 1–2 at first, increasing up to four per fascicle; hooks in neuropodia usually appearing from chaetigers 15–17 (usually 17), numbering 1–2 at first, increasing up to six per fascicle ( Fig. 5 ); hooks multidentate ( Figs 2H , 3J, 4G), with three ( Fig. 4I ) or four ( Fig. 4H ) pairs arranged in two vertical rows and a smallest uppermost tooth above main fang; hooks in neuropodia accompanied by 1–4 thin, long non-limbate capillaries. Ventral sabre chaetae broadly unilimbate, heavily granulated with sheaths ( Figs 2G , 3I), appearing from chaetiger 10.

Dorsal branchiae short, cirriform with rounded tip, four pairs on chaetigers 2–5 ( Fig. 4D ), first pair sometimes longer than last three pairs ( Fig. 3B ); first pair usually 1.5–2 × as long as notopodial postchaetal lamellae, up to about 3 × as long as, but not extending over two segments ( Figs 2B , 3B); second and third pairs similar in length or slightly longer than notopodial postchaetal lamellae, usually extending one segment, but slightly over than one segment in large specimens ( Figs 2C–D , 3F); last pair distinctly usually 2 × as long as notopodial postchaetal lamellae; branchiae with heavy ciliation at inner and outer margins ( Figs 2E , 3G); branchiae completely free from notopodial postchaetal lamellae.

Dorsal crest, lateral pouches, and ventral flaps absent.

Oocytes unknown.

Pygidium with one elongated, thick middorsal cirrus and one pair of short, thick ventral lappets, all bearing numerous non-motile sensory cirri up to 60 μm long ( Fig. 4F ).

COLORATION AND PIGMENTATION. Whitish color in live specimens with orangish brown pigmentations presented on the anterior part of prostomium, between anterolateral eyes of prostomium ( Fig. 3B ), and lateral paired ventral lappets of pygidium. In formalin- or ethanol-fixed specimens yellowish white color, pigmentation on prostomium usually remained ( Fig. 3C–D ), but pigmentation on pygidium usually fades or is completely lost.

Methyl green staining pattern (MGSP)

Twelve complete specimens were examined for MGSP. Anterior margin of prostomium, dorsal and lateral sides of peristomium, caruncle, margins of postchaetal lamellae and branchiae, pygidium weakly stained; staining almost faded out in about 2–3 hours and completely disappeared in about 2–3 days. Lateral and ventral sides of chaetigers 8–22 intensely stained, and narrow transverse bands along anterior edges of chaetigers 10–18 most intensely stained; the patterns remained for at least one week and faded out after about a month.

Habitat and distribution

Adults of this new species were found in muddy and silty sand in the intertidal zone of the Yellow Sea.

Genetics

Sequences of three gene fragments (COI, 16S rDNA, and 18S rDNA) were determined from four adult specimens of Prionospio expansa sp. nov. The length of obtained DNA sequences were 605 bp for COI, 532 bp for 16S rDNA, and 1,762 bp for 18S rDNA. The newly determined sequences have been registered in GenBank with the accession numbers OQ672519–22 (COI), OQ685963–6 (16S rDNA), and OQ685953–6 (18S rDNA). The intraspecific genetic distances were 0–0.2% in both COI and 16S rDNA, and no variation was detected in 18S rDNA. Based on available gene data of Prionospio species from GenBank, the new species is genetically closest to P. japonica from Northeast Asia (squares in Fig. 6 ). The genetic differences between sequences of the new species and those of P. japonica from Japan and Korea were 20.7% (97/469 bp, MW054868) in COI, 10.4% (59/469 bp, LC595695) in 16S rDNA, and 0.1% (1/1,619 bp, LC545865) in 18S rDNA.

Figures

Fig. 2. Drawing of Prionospio expansa sp. nov., paratype (NIBRIV0000900992). A. Anterior body without palps. B–E. Parapodium from chaetigers 2–5, front view. F. Unilimbate capillary from first notopodium. G. Ventral sabre chaeta from chaetiger 12. H. Neuropodial hooded hook from chaetiger 17. Scale bars: A = 0.2 mm; B–E = 0.1 mm; F–H = 20 μm.

Fig. 3. Images of Prionospio expansa sp. nov. A, C. Holotype (NIBRIV0000900991). B. Paratype (NIBRIV0000901000). D–J. Paratype (NIBRIV0000900992). A. Entire body with palps. B. Live specimen, dorsolateral view. C. Anterior end with palps, dorsal view. D. Anterior end without palps, dorsal view. E. Chaetiger 2, front view, branchia missing. F. Chaetiger 3, front view. G. Chaetiger 5, front view. H. Unilimbate capillary of first monopodium. I. Sabre chaeta of chaetiger 12. J. Lateral view of hooded hook in chaetiger 17, inset indicating front view of hooded hook. Abbreviation: pig = pigmentation. Scale bars: A = 0.5 mm; B–D = 0.2 mm; E–G = 50 μm; H–I = 20 μm; J = 10 μm.

Fig. 4. SEM images of two Prionospio species from Korean waters. A–I. Prionospio expansa sp. nov. A–B, D–F. Paratype (NIBRIV0000901890). C, G–I. Paratype (NIBRIV0000901891). J–K. Korean Prionospio japonica Okuda, 1935, non-type. A. Entire body without palp, dorsal view. B. Anterior end with seven chaetigers, dorsolateral view. C. Anterior end with eight chaetigers, dorsal view. D. Anterior end, front view. E. Frontal margin of prostomium, arrows indicating frontal small peaks. F. Pygidium with middorsal cirrus and paired ventral lappets. G. Hook of middle chaetiger, hood removed, lateral view. H. Hook of posterior chaetiger, lateral view. I. Hook of posterior chaetiger, ventrolateral view. J. Anterior end with seven chaetigers, dorsolateral view. K. Pygidium. Abbreviation: tcb = transverse ciliated bands. Scale bars: A = 0.5 mm; B–D = 0.1 mm; E = 10 μm; F = 20 μm; G = 2 μm; H–I = 1 μm; J–K = 0.2 mm.

Fig. 5. Relationships between the total chaetigers and the first appearances of neuro- and notopodial hooks in Prionospio expansa sp. nov.

Fig. 6. Maximum likelihood (ML) trees inferred from gene fragments of COI (469 bp), 16S rDNA (470 bp), and 18S rDNA (1,619 bp). The sequences of Prionospio expansa sp. nov. obtained in the present study are highlighted in bold. Numbers beside branches indicate ML bootstrap values of ≥ 50% as a percentage of 1000 bootstrap replications. The sequences of Spio filicornis (Müller, 1776) and Aonides aff. oxycephala (Sars, 1862) were used as outgroup taxa.