Rhynchospio aciliata, Lee & Min, 2022

Lee, Geon Hyeok & Min, Gi-Sik, 2022, Rhynchospio aciliata sp. nov., a new spionid species (Annelida, Spionidae) from the Korea Strait, ZooKeys 1100, pp. 191-205 : 191

publication ID	https://dx.doi.org/10.3897/zookeys.1100.80077
publication LSID	lsid:zoobank.org:pub:4F5DA6D8-8BBD-455E-88EA-EB3E89195950
persistent identifier	https://treatment.plazi.org/id/1F611CE8-58B5-48B3-9462-DF48AEE0FF0A
taxon LSID	lsid:zoobank.org:act:1F611CE8-58B5-48B3-9462-DF48AEE0FF0A
treatment provided by	ZooKeys by Pensoft
scientific name	Rhynchospio aciliata
status	sp. nov.

Treatment

Rhynchospio aciliata sp. nov.

Figs 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5

Type locality.

Korea Strait, Korea: Jeollanam-do, Wando-gun, Soan-myeon, Gahak-ri, Soan Island, 34°9'56.1"N, 126°39'29.8"E, intertidal sandflats.

Material examined.

Holotype: complete specimen (NIBRIV0000893855) (Fig. 3F View Figure 3 ), fixed in formalin. Paratypes: five complete (NIBRIV0000893849-53), 12 complete, 23 anterior fragments, 7 middle fragments, 9 posterior fragments (NIBRIV0000893854) fixed in formalin; 2 complete (NIBRIV0000893847-8), 1 anterior fragment (NIBRIV0000893846), 95% ethanol. All examined specimens were collected from the type locality, 25 May 2021.

Diagnosis.

Prostomium with 2 conical pointed frontolateral horns, extending posteriorly to anterior margin of chaetiger 1, with papilliform elevation on posterior part. Metameric nuchal organs brownish and oval, ciliary bands double-paired from chaetiger 1 to chaetigers 42-49. First notopodial postchaetal lamellae large and lanceolate. Anterior branchiae conspicuously large and foliaceous. Tridentate hooded hooks appearing from chaetigers 18-24, numbering 9 or 10 per fascicle. Transverse ciliated bands, ciliation on the inner branchiae, and intersegmental transverse cilia absent in anteriormost chaetigers. Sperm from chaetiger 12 to chaetigers 34-43. Oocytes from chaetigers 35-44 onwards, up to approximately 120 μm in diameter. Pygidium with 1 pair of stout, conical ventral cirri, and usually 4-6 pairs of thin, long dorsolateral cirri.

Description.

Holotype specimen complete with 85 chaetigers, approximately 0.9 mm wide and 7.0 mm long. Paratypes with 79-93 chaetigers, 0.8-1.1 mm wide, and 5.5-10.7 mm long. Yellowish-white in both live and formalin-fixed specimens (Fig. 3A, B, F View Figure 3 ).

Prostomium with 2 conical pointed frontolateral horns; transverse depression between anterior and middle part of prostomium (Fig. 5A View Figure 5 ); 2 pairs of black eyes arranged in a trapezoid, anterior pair crescent-shaped, more widely separated than posterior pair, and posterior pair round or slightly crescent-shaped; caruncle low and indistinct, extending posteriorly to anterior margin of chaetiger 1; conspicuous papilliform elevation on posterior part of prostomium; occipital antenna absent (Figs 2A View Figure 2 , 5A View Figure 5 ). Peristomium moderately developed, not forming lateral wings, partially encompassing prostomium posteriorly (Fig. 5B View Figure 5 ). Palp reaching back to chaetigers 4-7, with longitudinal groove lined with fine cilia. Nuchal organs metameric, brownish, oval (arrowheads in Fig. 4A View Figure 4 ), ciliary bands double-paired (Fig. 5C View Figure 5 ) from chaetiger 1 to chaetigers 42-49 (46 in holotype); first four pairs slightly curved or almost straight; from chaetiger 5, nuchal organs conspicuously curved inward (Fig. 5A, C View Figure 5 ).

Chaetiger 1 well developed, with large, lanceolate notopodial postchaetal lamellae and conical neuropodial postchaetal lamellae (Fig. 5B View Figure 5 ); notochaetae present. Branchiae from chaetiger 2 present almost throughout body, absent on last 5-9 chaetigers (Fig. 6D View Figure 6 ); anterior branchiae large, broad, and foliaceous, gradually becoming narrower and smallest in posterior chaetigers (Fig. 2B-F View Figure 2 ); branchiae separated from notopodial postchaetal lamellae; branchiae with distinct ciliation at inner margin present from chaetiger 6 (Figs 4A View Figure 4 , 5A View Figure 5 ). Notopodial postchaetal lamellae lanceolate to subtriangular, largest in anterior chaetigers (Fig. 2B View Figure 2 ), gradually becoming small with pointed tips in posterior chaetigers (Fig. 2C-F View Figure 2 ). Neuropodial postchaetal lamellae conical with rounded tips in first 2 chaetigers, becoming broadly rounded until about chaetiger 15, and becoming broad, low subrectangular posteriorly (Fig. 2B-F View Figure 2 ). Prechaetal lobes low and rounded in both rami (Fig. 5E View Figure 5 ).

Chaetae in notopodia all capillaries with sheaths; arranged in 2 indistinct rows in anterior chaetigers, more posteriorly arranged in a bundle; 8-12 capillaries very long, non-granulated capillaries in superiormost position at first 2 chaetigers (Fig. 2A View Figure 2 ); anterior-row capillaries slightly with heavy granulations and posterior-row capillaries longer, non-granulated in anterior chaetigers; granulations of anterior-row capillaries becoming faint posteriorly and completely disappear from chaetigers 40-50. Chaetae in neuropodia with sheathed capillaries and hooded hooks as well as sabre chaetae in inferior position, arranged in 2 rows (Fig. 5E View Figure 5 ); chaetae in anterior row shorter and stouter, heavily granulated and capillaries in posterior row rather thin, non-granulated in anterior chaetigers (Fig. 3C View Figure 3 ); 9 or 10 tridentate hooded hooks replacing posterior row of neurochaetae from chaetigers 18-24 (usually 19-21, 20 in holotype), covered with minute bristles (Fig. 5F View Figure 5 ); hooks with 2 small, upper teeth arranged in line above main fang (Figs 2I View Figure 2 , 3E View Figure 3 , 5F View Figure 5 ); 4 or 5 capillaries in inferiormost position usually present 2 or 3 segments before hook-bearing chaetigers; 4 or 5 sabre chaetae heavily granulated, with sheaths, appearing from about hook-bearing chaetigers (Figs 2H View Figure 2 , 3D View Figure 3 , 5E View Figure 5 ).

Transverse ciliated bands and intersegmental transverse cilia present from chaetiger 5 to almost throughout body (Fig. 5A View Figure 5 ), absent on last 6-9 chaetigers (Fig. 6D View Figure 6 ). Intersegmental lateral pouches positioned in front of superior part of neuropodial postchaetal lamellae, small in the beginning, appearing from chaetigers 13-15 (Fig. 2C-F View Figure 2 ). Glandular pouches indiscernible. Sperm from chaetiger 12 to chaetigers 34-43 (35 in holotype). Oocytes subspherical, from chaetigers 35-44 onwards (35 in holotype), up to approximately 120 μm in diameter (Fig. 4C View Figure 4 ); envelope approximately 5 μm thick, with external honey-combed surface but without vesicles at inner surface; single nucleolus approximately 12 μm in diameter. Embryos not observed in any of the examined specimens.

Pygidium with 1 pair of stout, conical ventral cirri, and usually 4-6 pairs (5 pairs in holotype, 1 specimen (NIBRIV0000893849) with 24 pairs) of thin, long dorsolateral cirri (Fig. 2G View Figure 2 ); occasionally some dorsolateral cirri bifid (Fig. 5D View Figure 5 ).

MGSP. Prostomium, peristomium, basal part of palps, margins of branchiae, intersegmental lateral pouches (Fig. 4B View Figure 4 ), notopodial, and neuropodial lobes were intensely stained (Fig. 4C View Figure 4 ). On the dorsal side, transverse ciliated bands across the dorsum were not distinctly stained (Fig. 4A View Figure 4 ). On the ventral side, 2 transverse bands per chaetiger were stained intensely (Fig. 4E View Figure 4 ). For at least 1 week after staining, the prostomium, peristomium, chaetiger 12 to chaetigers 34-43 remained stained (male fertile segments), and the ventral transverse bands in anterior and middle chaetigers conspicuously remained (Fig. 4D View Figure 4 ).

Etymology.

The specific name aciliata is a combination of the Latin prefix a - and the Latin word cilia, meaning "absence of cilia." This name refers to the absence of ciliation on the dorsum and inner margins of branchiae of the anteriormost chaetigers.

Habitat and ecology.

The new species was found in fine sand in the intertidal zone.

Distribution.

Soan Island, Korea.

Genetics.

The partial mitochondrial COI, 16S rDNA, nuclear 18S rDNA, and 28S rDNA sequences from three specimens of R. aciliata sp. nov. were determined. The GenBank accession numbers and sequence lengths of the species were as follows: ON206852-4 for COI (687 bp), ON206000-2 for 16S rDNA (517 bp), ON206003-5 for 18S rDNA (1,778 bp), and ON206006-8 for 356 bp (28S rDNA) (Table 1 View Table 1 ). The intra-specific genetic distances were 0-0.4% in 16S rDNA, and no variation was detected in the other three gene regions. Based on the available molecular data of Rhynchospio from GenBank, the new species is genetically the closest to R. cf. foliosa from Oregon, USA. The genetic distance between the new species and R. cf. foliosa was 6.9% (22/294 bp, KR607514) in 16S rDNA, 0.4% (4/1,723 bp, KR607515) in 18S rDNA, and 0.7% (2/351 bp, KP986490) in 28S rDNA (Table 2 View Table 2 ). Phylogenetic analyses showed that R. aciliata sp. nov. formed a monophyletic clade with R. cf. foliosa from Oregon, USA (Fig. 6 View Figure 6 ). This result implies that their close relationships share several morphological characteristics (see below). Unfortunately, the molecular information of R. foliosa from Japan (type locality) is still unknown. Further genetic studies on R. foliosa are needed to confirm their genetic relationships.