Pelagobia rubromaculata, Kolbasova & Neretina, 2021

Kolbasova, G. & Neretina, T., 2021, A new species of Pelagobia (Lopadorrhynchidae, Annelida), with some notes on literature records of Pelagobia longicirrata Greeff, 1879, Zootaxa 5023 (1), pp. 77-92 : 80-84

publication ID	https://doi.org/ 10.11646/zootaxa.5023.1.4
publication LSID	lsid:zoobank.org:pub:4AA8C804-6B4D-41F4-84CF-5CCFB59CC963
persistent identifier	https://treatment.plazi.org/id/F507B8D0-8FF3-4F47-935E-16F013F68B29
taxon LSID	lsid:zoobank.org:act:F507B8D0-8FF3-4F47-935E-16F013F68B29
treatment provided by	Plazi
scientific name	Pelagobia rubromaculata
status	sp. nov.

Treatment

Pelagobia rubromaculata View in CoL sp. nov.

Figs 2–6 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6

Diagnosis. Prostomium triangle, eyes with lenses. Pair of pharyngeal jaws. Tentacular cirri without aciculae. Shafts with fine spines, blades serrated. Pygidium with two rudimental appendages.

Material examined. Holotype ZMMU MSU WS14781 View Materials , paratypes ZMMU MSU WS14782 View Materials and ZMMU MSU WS14783 View Materials (8.04.2019, 0–10 m, 12°4′32″ N, 109°18′48″ E, Noi Island ) preserved in 96% ethanol GoogleMaps . Paratypes ZMMU MSU WS14775 View Materials – ZMMU MSU WS14777 View Materials (8.04.2019, 0–10 m, 12°4′32″ N, 109°18′48″ E, Noi Island ), mounted on an aluminum stub and sputter-coated with an Au-Pd mixture after SEM GoogleMaps .

Other material: paratypes ZMMU MSU WS14784–14785 View Materials (8.04.2019, 0–10 m, 12°4′32″ N, 109°18′48″ E, Noi Island ) in 96% ethanol GoogleMaps .

Material used for DNA extraction: ZMMU MSU XZ4956–4958 View Materials (8.04.2019, 0–10 m, 12°15′53″ N, 109°20′36″ E, Dung Island ) GoogleMaps , ZMMU MSU XZ4959 View Materials and XZ4960 (8.04.2019, 0–10 m, 12°4′32″ N, 109°18′48″ E, Noi Island ) GoogleMaps .

Type material. Holotype: ZMMU MSU WS14781 View Materials ( Fig. 2A View FIGURE 2 ). Adult complete specimen with 14 segments. Body c-curved, pharynx extruded. Prostomium 120 µm long, 200 µm wide, with pair of bright red spots on end. Tentacular cirri of 200 µm long. Body length 2 mm, maximum width excluding parapodia 330 µm. Parapodia 120–330 µm long, chaetae 240–320 µm long. Pygidium with pair of short cirri. Body white, non-transparent, with 10 pairs of brown spots on base of 1– 10 pairs of parapodia.

Paratype ZMMU MSU WS14782 View Materials ( Fig. 2B View FIGURE 2 ). Adult female, full of eggs. Body s-curved, with 14 segments. Pygidium lost, pharynx extruded. Prostomium 120 µm long, 200 µm wide, with pair of bright red spots on end. Tentacular cirri of 180 µm long. Body length 2 mm, maximum width without parapodia 415 µm. Parapodia 100–250 µm long, chaetae 240–300 µm long. Body white, non-transparent, with 11 pairs of brown spots on base of 1–11 pairs of parapodia .

Paratype ZMMU MSU WS14783 View Materials ( Fig. 2C View FIGURE 2 ). Adult complete specimen with 14 segments. Pharynx extruded. Prostomium 120 µm long, 200 µm wide Tentacular cirri of 200 µm long. Body length 1.8 mm, maximum width without parapodia 360 µm. Parapodia 110–250 µm long, chaetae 100–240 µm long. Pygidium with pair of short cirri. Body white, non-transparent, with 11 pairs of brown spots on base of 1– 11 pairs of parapodia .

Paratype ZMMU MSU WS14775 View Materials . Adult complete specimen with 12 segments. Prostomium 130 µm long, 200 µm wide. Pair of short filiform antennae and pair of short filiform palps. Two pairs of tentacular cirri of 180 µm long on tentacular segment. Body length 1.6 mm, maximum width excluding parapodia 230 µm. Parapodia 100–180 µm long, chaetae 200–210 µm long. Pygidium with pair of short cirri .

Paratype ZMMU MSU WS14776 View Materials . Adult complete specimen with 14 segments. Prostomium 110 µm long, 170 µm wide. Pharynx everted. Pair of short filiform antennae and pair of short filiform palps. Two pairs of tentacular cirri of 180 µm long on tentacular segment. Body length 1.6 mm, maximum width excluding parapodia 230 µm. Parapodia 100–180 µm long, chaetae 200–210 µm long. Pygidium with pair of short cirri. Each pygidial cirrus ends with tiny terminal papilla .

Paratype ZMMU MSU WS14777 View Materials . Adult specimen with 16 segments. Prostomium 150 µm long, 200 µm wide. Pharynx everted .

Pair of short filiform antennae and pair of short filiform palps. Two pairs of tentacular cirri of 200 µm long on tentacular segment. Dorsal cirrus on third right parapodium lost. Body length 2.3 mm, maximum width excluding parapodia 400 µm. Parapodia 120–250 µm long, chaetae 200–260 µm long. Pygidium with pair of short cirri.

Description. Body flattened, fusiform, 1.5–2.3 mm long, with 11–15 segments ( Figs 2A, B, C View FIGURE 2 ). Both live and preserved worms semi-transparent, white, with two or four rows of brownish-red spots along dorsal side on parapodial bases ( Figs 2A, B, C View FIGURE 2 , 3E View FIGURE 3 ). Prostomium triangle, with two pairs of thin filiform appendages (pair of antennae and pair of palps), of about 0.75 length of prostomium ( Figs 3A View FIGURE 3 , 4A, B View FIGURE 4 ). Some specimens with bright red spots on bases of antennae ( Fig. 2B View FIGURE 2 ). Red eyes with lenses on dorsal side of prostomium ( Fig. 3A View FIGURE 3 ). Nuchal organs indistinct, accrete to latero-posterior sides of prostomium ( Figs 2A, B, C View FIGURE 2 , 3A View FIGURE 3 ). Pharynx with pair of small jaws; each jaw consists of basal part and falcate proximal one ( Figs 3A, B View FIGURE 3 ). Tentacular segment with minute parapodia with aciculae and fascicles of 3–4 compound chaetae ( Figs 3A View FIGURE 3 , 5A View FIGURE 5 ). Two pairs of short tentacular cirri of subequal length, reaching posterior edge of third body segment ( Figs 3A View FIGURE 3 , 4A, B View FIGURE 4 , 5A View FIGURE 5 ). Acicular structures in tentacular cirri absent. Parapodia of second segment without dorsal cirri ( Figs 3A View FIGURE 3 , 4A View FIGURE 4 , 5A View FIGURE 5 ). From third segment all parapodia with digitiform, taper- ing dorsal and ventral cirri; dorsal cirri reach nearly end of chaetae; ventral cirri slightly shorter ( Figs 3A, C View FIGURE 3 , 4A View FIGURE 4 , 5A View FIGURE 5 ). Each parapodium with tuft of 16—24 chaetae and one thick median projecting acicula ( Fig. 3C View FIGURE 3 ). All chaetae compound spinigers ( Fig. 3D View FIGURE 3 , 6A View FIGURE 6 ). Shafts long, heterogomph, with numerous fine denticles (using light microscopy difficult to see even under oil immersion) ( Figs 3D View FIGURE 3 , 6A, C View FIGURE 6 ). Blades serrated ( Figs 3D View FIGURE 3 , 6A, C View FIGURE 6 ). Pygidium with two short conical cirri terminating with papillae ( Fig 3E View FIGURE 3 , 4A, B View FIGURE 4 , 5B View FIGURE 5 ).

Etymology. The species name is a combination of the Latin adjective ‘maculatum’ referring to the coloured speckles that these worms have dorsally, and ‘rubrum’ referring to the red colour of these speckles.

Type locality. Collected in the Nhatrang Bay of the South China Sea, depths from 0–10 m.

Distribution. South China Sea, Spratly Islands, Taiwan, Vietnam.

Remarks. Pelagobia rubromaculata sp. nov. differs from P. serrata by the presence of eyes ( Southern 1909; Ushakov 1972; Isaychev et al. 2012). From P. longicirrata it differs by the shape of prostomium and by short tentacular cirri. Pelagobia longicirrata has pentagonal prostomium and nuchal organs forming distinct globular knobs or lappets on the lateral sides of the head, whereas P. rubromaculata sp. nov. has triangle prostomium and nuchal organs adherent to the cephalic lobe. Also, P. longicirrata has tentacular cirri reaching to 5–6 segment in contrast to tentacular cirri of P. rubromaculata sp. nov. reaching only the posterior edge of the third segment. Pelagobia rubromaculata sp. nov. has numerous denticles on chaetal shafts, that are minute and are hard to see with a light microscope. Pelagobia longicirrata has smooth chaetal shafts ( Greeff 1879; Southern 1909; Isaychev 2015; Kolbasova 2020). Ushakov (1972) noted fine spines on chaetal shafts for some P. longicirrata specimens from the Pacific Ocean, but he interpreted it as morphological variation.

Living P. rubromaculata sp. nov. differs from P. longicirrata by the colour pattern with red spots, that may fade after formalin fixation but are retained in those stored in alcohol. Usually, the colour pattern of living P. longicirrata describes as white-yellowish or white with yellow spots ( Greeff 1879; Ushakov 1972; Isaychev et al. 2012). Specimens from the Arctic are white with yellow nuchal organs and with orange spots on the lateral side of each segment and on a base of parapodial cirri (Kolbasova et al. 2020). Living P. serrata is also white with yellow spots on the lateral side of each segment ( Southern 1909).

DNA. As the 28S gene sequences for Pelagobia from the Antarctic and South Atlantic are absent in the Gen Bank, we made the single 18S tree (not shown) and the concatenated 18S and 28S genes tree ( Fig. 7 View FIGURE 7 ). The concatenated 18S and 28S genes tree ( Fig. 7 View FIGURE 7 ) and the single 18S gene tree (not shown) have the same topology, but the concatenated tree based on two genes resolves better. The topology of the resulting trees made both by the Bayesian and maximum likelihood (ML) analyses are congruent (see Fig. 7 View FIGURE 7 ).

Pelagobia rubromaculata sp. nov. forms a separate clade with good support ( Fig. 7 View FIGURE 7 ). Surprisingly, P. longicirrata divides into several clades in the accordance with the geographical distribution of samples: the Arctic clade, the Central Atlantic clade and the South Atlantic clade. The specimens from the Antarctic form did not cluster into a clade due to variability of the 18S rDNA gene.

Nuclear 18S and 28S sequence data of P. rubromaculata sp. nov. obtained in this study are available in Gen- Bank under accession numbers given in Table 2. The 18S (1750 bp) p-distance between P. rubromaculata sp. nov. and P. longicirrata from the Equatorial Atlantic is 2.8%. For P. longicirrata from the Antarctic it is 2.7–2.9%. For Pelagobia sp. from the Angola Basin the p-distance is 4.8%, for P. longicirrata from the Arctic it is 2.7%. The 28S (413 bp) p-distance is 4.3–5% for P. longicirrata from the Equatorial Atlantic, and 2.4% for P. longicirrata from the Arctic ( Table 3).