Pseudoscalibregma parapari, Mendes & Paiva & Rizzo, 2024

Mendes, Samuel Lucas Da Silva Delgado, Paiva, Paulo Cesar De & Rizzo, Alexandra E., 2024, New species of Pseudoscalibregma Ashworth, 1901 (Annelida: Scalibregmatidae Malmgren, 1867) from Brazil, Zootaxa 5399 (1), pp. 19-36 : 28-32

Pseudoscalibregma parapari sp. nov.

Figures 6–8

https://zoobank.org/NomenclaturalActs/ 5BF234D7-44E7-4B07-A47A-3F89974F64EF

Type material. UERJ 9169 (Holotype) : AMBES12 ; CANWN6 R2 , 19º 53’ 27,27” S, 39º 32’ 59,82” W , coll. 28 Jun 2013, 970 m, complete. UERJ 9221 (Paratype) : AMBES16 , CANWN7 R1 , 19.969844 S, 39.527303 W , coll. 13 Jan 2012, 1,300 m, complete, in two halves. UERJ 9218 (Paratypes) : AMBES12 , CANWN6 R1 , 19º 53’ 27,27” S, 39º 32’ 59,82” W , coll. 13 Jan 2012, 1,023 m, 2 spec, 1 incomplete anterior fragment and 1 complete.

Diagnosis. Body arenicoliform, expanded over chaetigers 4–11. Body surface covered by secondarily annulated rings, each made by inconspicuous rectangular pads anteriorly and smaller squared to rectangular pads posteriorly. Chaetiger 1 biannulated dorsally and ventrally, chaetigers 2–3 triannulated, quadriannulated from chaetiger 4 onwards. Dorsal and ventral cirri present from chaetiger 14. Spines present on chaetigers 1–2, 5 per fascicle, with pointed tips. Lyrate chaetae from chaetiger 2, 4–5 per fascicle, with subequal tynes.

Description. Holotype complete, 4 mm long, 1 mm wide across expanded anterior region, 0.4 mm wide across narrower posterior region, with 33 chaetigers. Small sized species, Paratypes measuring 3.5–5mm long, 0.2 mm – 1 mm wide, for 30–35 chaetigers. Body arenicoliform, expanded over chaetigers 4–11. Colour in alcohol pale tan to yellowish. Body surface covered by secondarily annulated rings, each one formed by inconspicuous rectangular pads anteriorly and smaller squared to rectangular pads posteriorly. Pads sometimes with small individual dark blue or black glands within, due to entangled cellular tubules.

Rounded prostomium, with 2 short spherical horns, both projected laterally ( Figs 6A ; 7A, B ; 8A ). Eyes absent. Nuchal organs not observed. Peristomium achaetous, as single annulus both dorsal and ventrally ( Figs 6A , 7A–B ). Proboscis smooth. Mouth’s superior lip nature obscure in type material. Inferior lip with up to 6 lobules, these formed by the contribution of ventral groove’s first pad. Ventral groove present from chaetiger 1, first pad as part of mouth, followed by paired triannulated pads on each chaetiger, forming a mid-line ridge throughout ( Figs 6A , 7C ). Posterior pads poorly marked and smaller than anterior pads.

Chaetiger 1 biannulated both dorsal and ventrally, chaetigers 2–3 triannulated, quadriannulated from chaetiger 4 onwards ( Figs 6A , 7A, B ). Parapodial lobes rounded anteriorly; from mid-body to posterior chaetigers, parapodial lobes rounded to squared dorsally, subtriangular to ellipsoid ventrally, parapodial lobes always shorter than cirri ( Figs 6D–F , 7G );parapodial gradually changing to thinner and smaller from mid-body onwards. Dorsal and ventral cirri present from chaetiger 14; fist cirri as rounded projections with smooth tips, then subtriangular and finally lanceolated on posteriormost chaetigers ( Figs 6D–F , 7E–H ), all with large tubular glands within. Interramal papillae from chaetiger 14, knob-like, with thin tubular glands within ( Figs 6D , 7G ).

Short spinous setae present from chaetiger 1, 5 per fascicle, with pointed tips ( Fig. 8B ). Lyrate chaetae present from chaetiger 2 ( Figs 6B , 7D ), 4–5 per fascicle, with subequal tynes (tynes’ length ratio: 1.2). Capillaries organized in 2 rows anteriorly, 1 one row posteriorly. Parapodial lobes reduced on chaetiger 1, with smaller chaetae. Pygidium triannulated, damaged on all specimens, but a short terminal margin, from which emerges a crown with about 15 lobules ( Fig. 7I , 8C ). Pygidial cirri missing.

Remarks. The new species is close to P. parvum ( Hansen, 1879) , P. usarpium ( Blake, 1981) , and P. palmeri ( Blake, 2015) in the shape of prostomium, and body annulation. However, P. palmeri and P. usarpium possess lyrate chaetae from chaetiger 3, whereas in P. parapari sp. nov. and P. parvum lyrate chaetae emerge from chaetiger 2. Interestingly, P. parvum diverges morphologically from them by the presence of spinous chaetae with bifurcated tips. Members of all these species share lyrate chaetae with similar tynes ratio.

Regarding the secondary body annulations, P. usarpium is unique in the genus due to its complex annulation pattern, being quadriannulate on anterior chaetigers and pentannulate on posterior chaetigers. Pseudoscalibregma parapari sp. nov. chaetiger 1 is biannulated, chaetigers 2–3, triannulated, and quadriannulated from chaetiger 4 onwards. This pattern also differs P. parvum , which have two rows of pads on notopodia plus a single row of pads separating superior and inferior transverse limits of chaetigers ( Bakken et al. 2014). Pseudoscalibregma palmeri and P. parapari sp. nov. present a similar annulation pattern, differing on posterior chaetigers, which are quadriannulated in P. parapari sp. nov. and triannulated in P. palmeri . Importantly, as mentioned above, P. parapari present a rounded prostomium, lyrate chaetae from chaetiger 2, and notopodial and neuropodial lobes differing in shape; whereas P. palmeri present a squared prostomium, lyrate chaetae from chaetiger 3 and parapodial lobes of same conical shape.

Despite of the absence of reproductive characters, all type specimens of P. parapari sp. nov. have at least 30 chaetigers, exceeding the 22–24 chaetiger stage (sensu Blake 2015).This information is relevant, because this species is relatively smaller than its congeners, but when a scalibregmatid with dorsal and ventral cirri on parapodia reach this number of chaetigers, it is probably out of the cryptic “ Pseudoscalibregma -like” ontogenetic state observed by Blake (2015). Hence, important features such as the emergence order of lyrate chaetae, spinous chaetae and presence of branchial lobes on first chaetigers can be determined without confusing juveniles as adults.

Etymology. The specific epithet “ parapari ” was chosen to honor the polychaete researcher Dr. Julio Parapar at Universidad Da Coruña (UDC, Spain), for his contributions to the polychaetes taxonomy, ecology, and morphology, and specially for his recent review on the family Scalibregmatidae , providing an updated list of valid species and directing important topics for future research.

Ecology. Finally, except for P. parvum from shallow records, P. usarpium , P. palmeri share similar bathymetric records, not exceeding the range of 500 to 2,000 meters deep. The new species P. parapari sp. nov. was sampled from a bathymetric range varying from 970–1,300 m deep, on predominantly muddy sediments. Hence, this species also lies within the bathymetric interval of the congeners P. usarpium and P. palmeri , that are not abyssal species, but also do not occur in intertidal to shallow subtidal zones.

Figures

FIGURE 6. Pseudoscalibregma paraparisp.nov. Holotype (UERJ 9169) representation(A).Anteriorbody withfirst chaetigerous segments in ventral view; (B). Lyrate chaeta; (C). Spinous chaeta; (D). Section of mid-body parapodium, anterior view; (E). Section of posterior body parapodium, anterior view; (F). Section of posteriormost parapodium, anterior view.Abbreviations: dC = dorsal cirrus; Hor = prostomial horn; iP = interramal papilla; Pe = peristomium; Pr = prostomium; vC = ventral cirrus.

FIGURE 7. Pseudoscalibregma parapari sp. nov., Holotype (UERJ 9169) under light microscopy. (A). Anterior body with first chaetigerous segments, dorsal view; (B). Anterior body with first chaetigerous segments, ventral view; (C). Mid-body, ventrolateral view, stained with Shirlastain A; (D). Lyrate chaetae; (E). Midbody dorsal cirrus in detail, stained with Shirlastain A. (F). Posterior body dorsal cirrus in detail, stained with Shirlastain A; (G). Section of midbody parapodium, anterior view; (H). Lateral view of posterior body, stained with Shirlastain A; (I). Posterior end, ventral view.Abbreviations: Ch1 = chaetiger 1; Ch2 = chaetiger 2; dC = dorsal cirrus; iP = interramal papilla; Nel = neuropodial lobe; Nol = notopodial lobe; Pe = peristomium; PgM = pygidial margin; Pr = prostomium; vC = ventral cirrus.

FIGURE 8. Pseudoscalibregma parapari sp. nov. (UERJ 9213), sacrificed specimen under SEM. (A). Anterior body, ventral view; (B). Spinous chaetae in detail; (C). Final body, dorsal view.Abbreviations: dC = dorsal cirrus; Hor = horn; Pg = pygidium; Sc = Spinous chaeta.