Pseudoscalibregma magalhaesi, 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 : 25-28

Pseudoscalibregma magalhaesi sp. nov.

Figures 4–5

https://zoobank.org/NomenclaturalActs/ 6944B20D-3505-4F22-B6DC-3188CFC6E609

Type material. UERJ 8749 (Holotype) : AMBES1 , FOZ13 R2 , 19º 47’ 32,83” S, 39º 43’ 15,08” W, coll. 15 Dec 2010, 41 m ; UERJ 8748 (Paratype) : AMBES1 , FOZ13 R1 , 19.792453 S, 39.720856 W, coll. 15 Dec 2010, 41 m.

Diagnosis. Medium sized species; with trapezoidal prostomium and pair of eyes. Ventral groove present from chaetiger 1, with first and second pads fused to each other, asymmetrical, and rounded anteriorly, contributing to mouth’s formation. Chaetiger 1 triannulated, quadriannulated from chaetiger 2 onwards. Dorsal and ventral cirri from chaetiger 14, gradual changing in size and shape from midbody to posterior chaetigers. Interramal papillae from chaetiger 14. Spinous chaetae on chaetigers 1–2, 4–5 per fascicle, curved at midlength, with pointed tips. Lyrate chaetae present from chaetiger 3, 4–5 per fascicle, with uneven tynes.

Description. Holotype complete, 7 mm long, 1 mm wide across expanded anterior region, 0.2 mm wide across narrow posterior region, with 40 chaetigerous segments. Medium sized species, juvenile Paratype measuring 1.5 mm long, and 0.1 wide for 23 chaetigerous segments. Body arenicoliform, expanded on chaetigers 7–12. Pale tan in alcohol. Body surface covered by secondarily annulated rings. Anterior region secondary annuli composed by inconspicuous rectangular pads, hardly conspicuous on type material under stereomicroscopy. Ventrally and dorsally, these pads may present small individual dark blue to blackish glands within, consisting of entangled cellular tubules at center of each pad.

Trapezoidal prostomium, with a pair of long and thin horns, both projected laterally ( Figs 4A , 5A ). Eyes present, on the middle of prostomium ( Figs 4A , 5A ). Nuchal organs observed on paratype, as dorso-lateral sac-like everted structure between prostomium and peristomium. Peristomium achaetous, biannulated ( Fig. 4A ). Proboscis not observed. Ventral groove present from chaetiger 1, with first and second pads fused to each other, asymetrical, participating in mouth’s formation ( Fig. 4A ). Following pads paired to one chaetiger only. Pads from chaetiger 3 symmetrical, squared to rectangular on anterior and midbody chaetigers, poorly marked and smaller posteriorly.

Chaetiger 1 triannulated, quadriannulated from chaetiger 2 onwards ( Figs 4A , 5A ). Dorsal and ventral cirri present from chaetiger 14. Dorsal and ventral cirri triangular, gradually changing in size and shape from their beginning, on chaetiger 14, to final chaetigers ( Figs 4D–F , 5G–H ); first cirri as broad rounded bases terminating by smooth tip; bases gradually thinner and longer as cirri progressively enlarge; densely packed dark blue to blackish tubular glands fill cirri within ( Fig. 5D–F ). Interramal papillae from chaetiger 14, as rounded structure, with granular contents within ( Fig. 5D ). Parapodial lobes gradually changing in size and shape ( Figs 4D–F , 5G–H ); asymmetrical on anterior chaetigers, with broader and rounded bases on mid-body chaetigers, and with thin lanceolate tip on posterior chaetigers. Parapodial lobes progressively smaller and thinner as cirri enlarge, from mid-body to posterior chaetigers ( Figs 4D–F , 5G–H ).

Spinous chaetae present from chaetigers 1–2, 4–5 per fascicle, curved at mid-length, with pointed tips ( Figs 4B , 5B ). Lyrate chaetae present from chaetiger 3 ( Figs 4C , 5C ), 4–5 per fascicle, with subequal tynes (tynes’ length ratio: 1.3). Capillaries organized in 3 rows anteriorly, 2 rows in mid-body and 1–2 rows in posterior body chaetigers; chaetiger 1 reduced, with shorter chaetae; from chaetigers 1–5, anterior rows progressively longer, all about same length from chaetiger 6 onwards. Pygidium damaged on analyzed specimens.

Remarks. The new species presents morphological affinities to P. usarpium Blake, 1981 , P.palmeri Blake, 2015 , and P. orientalis Imajima, 2009 . Members of all those species have long prostomial horns, squared to trapezoidal prostomium, lyrate chaetae with subequal tynes and short spinous chaetae on anterior chaetigers. Members of P. glandipodium also have relatively long horns, but they lack spinous chaetae on first chaetigers, differing from all its congeners, including the new species herein described. Specimens of P. magalhaesi sp. nov. have triannulated chaetiger 1, chaetigers quadriannulated from chaetiger 2 onwards. This is different from members of P. usarpium , which have quadriannulated anterior chaetigers, while individuals of P. orientalis have all chaetigers biannulated, and members of P. palmeri have biannulated chaetigers 1–2, quadriannulated on midbody chaetigers, and triannulated on posterior body chaetigers. In specimens of P. orientalis , the lyrate chaetae first appear on chaetiger 2, whereas in members of P. usarpium , P. palmeri and P. magalhaesi sp. nov. they begin from chaetiger 3.

Some important differences between specimens of these species come from their parapodial cirri. Pseudoscalibregma orientalis and P. palmeri present atypical cirri morphologies, long and digitate cirri on specimens of P. orientalis , asymmetrical on P. palmeri chaetigers. On the other hand, P. usarpium and P. magalhaesi sp. nov. present the typical parapodial cirri morphology, considering species of Pseudoscalibregma . The major differences between P. usarpium and P. magalhaesi sp. nov. concerns the relation of size and shape among parapodial lobes and cirri through the body. Pseudoscalibregma usarpium , dorsal cirri are always shorter than parapodial lobes and there is no gradual change on parapodial lobes and cirri along the body.Additionally, individuals of the species mentioned above do not have any kind of photoreceptors on prostomium, except for P. magalhaesi sp. nov. Regarding bathymetric range, P. usarpium , P. orientalis and P. palmeri share a similar depth of up to 2000 m deep, occupying deeper waters than P. magalhaesi sp. nov., which was collected from about 40 m deep.

Etymology. The specific epithet “ magalhaesi ” was chosen in honour to the Brazilian polychaete researcher Dr. Wagner Magalh„es at Bahia Federal University (UFBA), for his important contributions to polychaete science, especially on cirratulids taxonomy, and to celebrate our friendship.

Ecology. This species was found on shallower waters when compared to its congeners and to the new species described in this work. Both holotype and paratype were found in the same sampling station, at 41 meters deep, near “Rio Doce” river mouth.

Figures

FIGURE 4. Pseudoscalibregma magalhaesi sp. nov. Holotype (UERJ 8749) representation(A).Anterior body,first chaetigerous segments in ventral view; (B). Spinous chaetae; (C). Lyrate chaeta; (D). Section of a 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 5. Pseudoscalibregma magalhaesi sp. nov., Holotype (UERJ 8749) under light microscopy stained with Shirlastain A. (A). Anterior body in ventral view; (B). First chaetiger; (C). Lyrate chaetae from mid-body parapodium; (D). Section of mid-body parapodium, anterior view; (E). Mid-body ventral cirrus in detail; (F). Mid-body dorsal cirrus in detail; (G). Gradual transformation in size and shape of cirri and parapodial lobes; (H). Posterior body chaetigers.Abbreviations: Dc = dorsal cirrus; Ip = interramal papilla; Ly = lyrate chaeta; Nol = notopodial lobe; Vc = ventral cirrus.