Poecilochaetus perequensis Santos & Mackie

Santos, Cinthya S. G. & Mackie, Andrew S. Y., 2008, New species of Poecilochaetus Claparède, 1875 (Polychaeta, Spionida, Poecilochaetidae) from Paranaguá Bay, southeastern Brazil, Zootaxa 1790, pp. 53-68 : 61-66

publication ID	https://doi.org/ 10.5281/zenodo.182524
DOI	https://doi.org/10.5281/zenodo.6235439
persistent identifier	https://treatment.plazi.org/id/621CBD28-5363-2441-05D3-219EB269FBB7
treatment provided by	Plazi
scientific name	Poecilochaetus perequensis Santos & Mackie
status	sp. nov.

Treatment

Poecilochaetus perequensis Santos & Mackie View in CoL sp. nov.

Figures 26–50 View FIGURES 26 – 36 View FIGURES 37 – 42 View FIGURES 43 – 50

Material examined. Just northwest of where Perequê Creek enters Paranaguá Bay, Paraná (25°33.83’S, 48°21.33’W); muddy sand and standing water at mid-tide level. Holotype ( MCEM 1292) 1 dissected paratype ( MCEM 1293), 1 paratype ( MCEM 1294), 1 dissected paratype ( NMW.Z.1998.082.0009), 19 paratypes ( NMW.Z.1998.082.0010–0014), 2 paratypes ( BMNH 2008.157–2008.158), 1 paratype (ZMUC-POL-1953), 1 paratype (LACM-AHF POLY 2195).

Other material examined. Mouth of Maciel River, Paranaguá Bay, silty sand, 15 m, (VIR 9802), 3 specimens; Gamboa do Maciel, 1 specimen (C. Santos); Ilha das Cobras (25°28.9' S, 48°26.0' W), silty sand, 4 m, 4 specimens (VIR 9796).

Description. Holotype entire with 106 chaetigers, 36 mm long and 1.40 mm wide from tip to tip of ampullaceous parapodia. Dissected paratype (MCEM 1293) entire with 90 chaetigers, 23 mm long and 1.25 mm wide. Second dissected paratype (NMW.Z.1998.032.0009) entire (now in 2 pieces) with 95 chaetigers, 25 mm long and 1.20 mm wide. Other paratypes (1.0-1.7 mm wide), mostly fragmented; largest complete paratype (NMW.Z.1998.032.0014) 106 chaetigers, 41 mm long and 1.65 mm wide.

Prostomium small, rounded pyramidal, longer than wide, anterior margin concave or straight; positioned between notopodia of chaetiger 1 ( Figure 26 View FIGURES 26 – 36 ). Two pairs of small subdermal dark brown to black eyes; anterior pair round to reniform on short flat frontal part of prostomium, other pair smaller and round to bar-shaped, set closer together on posterior base of domed part.

Peristomium small, collar-like, surrounding prostomium laterally and giving rise to 3 nuchal lobes posteriorly ( Figure 26 View FIGURES 26 – 36 ). Median lobe longer, of moderate length, reaching up to chaetiger 4 or 5. Lateral lobes short, divergent, basally fused to median, reaching chaetiger 2 or 3. Anteriorly grooved palps, long, tapering, reaching chaetiger 30–35; short basal part expanded, overlapping posterior dome of prostomium. Margins of palp groove adorned with dense papillae of two types, long slender cirriform (25–75 µm long) and shorter (7–15 µm), cirriform to clavate, forms. Cirriform papillae often distally narrowed, with short digitiform tips. Lateral surfaces of palps longitudinally with 3 sparse rows of long cirriform papillae; rows irregular and, in distal regions, increasingly positioned toward abfrontal surfaces. Long, blunt cylindrical facial tubercle from upper margin of mouth, just below prostomium ( Figure 26 View FIGURES 26 – 36 ).

Ventral surfaces of chaetigers 1 and 2, and margins of mouth, covered with tiny pale yellow, rounded tubercles. Parapodial faces of anterior chaetigers with some sparsely distributed and barely visible tubercles appearing, as for other body surfaces, smooth (under zoom microscopy, x40). Ventrolateral surfaces of chaetigers 6 and 7 slightly tuberculate. Obtuse triangular chitinous plate on posterior dorsum of chaetiger 9; pale straw to light reddish brown in colour.

Chaetiger 1 large, directed forwards; neuropodial postchaetal lobes long, cirriform, notopodial lobes short, triangular ( Figure 27 View FIGURES 26 – 36 ). Neuropodial postchaetal lobes of chaetigers 2–6 short ( Figures 28–31 View FIGURES 26 – 36 ), lanceolate; longest on chaetiger 2 ( Figure 28 View FIGURES 26 – 36 ), shortest on chaetigers 4–6 ( Figures 30-31 View FIGURES 26 – 36 ). Notopodial postchaetal lobes on chaetigers 3, 4 and 6 of similar size and shape to respective neuropodial lobes, those of chaetigers 2 and 5 much longer.

Ampullaceous postchaetal lobes on chaetigers 7–13 ( Figures 32–35 View FIGURES 26 – 36 ). Wide basal parts of ampullaceous lobes glandular, distal parts smooth and slightly iridescent.

Postchaetal lobes on chaetiger 14 ( Figure 36 View FIGURES 26 – 36 ) similar to those on chaetiger 6. Thereafter, postchaetal lobes of both rami become narrower and shorter ( Figures 37–40 View FIGURES 37 – 42 ). In posterior region, postchaetal lobes cirriform; notopodial lobes slightly longer than neuropodial ones.

Interramal cup-like sensory papillae, with distal tufts of cilia, on chaetigers 1–5 ( Figures 27–30 View FIGURES 26 – 36 ) and 10– 15 (degree of protrusion variable after chaetiger 10), lacking on chaetigers 6–9. On following segments, sensory organs sessile, evident only as single projecting tufts of cilia ( Figure 39 View FIGURES 37 – 42 ). In posterior region (from about chaetiger 70–80), sensory organs again projecting as low cilia-bearing papillae. Interramal cirri absent. Branchiae absent.

Pygidium with small terminal anus and three ventral anal cirri; longer paired cirri arising just above short unpaired one, latter sometimes bifurcate ( Figures 41, 42 View FIGURES 37 – 42 ). Length ratio of superior to inferior cirri 2:1.

Chaetiger 1 with long, slender capillaries, arranged fan-like in both rami, forming cephalic cage; notochaetae longer. Notopodial capillaries smooth (viewed at x400 magnification), slightly hirsute (at x1000). Most neuropodial capillaries of chaetiger 1 appear distinctly annulated where concentric rings of fine hairs occur; transverse annulations on other neurochaetae and notochaetae indistinct. Neuropodia of chaetigers 2 and 3 with 4-5 hirsute falcate hooks ( Figure 43 View FIGURES 43 – 50 ). Several short slender capillaries (3–4) superior to emergent hooks in both chaetigers; single, partially formed, hooks seen embedded below bases of capillaries. Notopodia of same chaetigers with, slender capillaries; these and neuropodial ones smooth or with barely visible hairs (x1000). Following 2 chaetigers with capillaries only, some obviously hirsute (x400). Spinose chaetae appear in superior part of notopodia from chaetiger 6 (occasionally 5) and in inferior part of neuropodia from chaetiger 7 (occasionally 8).

Chaetae markedly different from chaetiger 17 (one from 18); long, plumose capillaries appear superiorly and inferiorly in both rami, and larger, sympodial spinose chaetae replace earlier spinose chaetae. In addition, 6–8 robust, heavily hirsute, capillaries with plumose tips project from small conical parapodia. These robust capillaries completely replaced by aristate chaetae over following 2–3 chaetigers and intermediate forms can occur ( Figure 44 View FIGURES 43 – 50 a, b); aristate chaetae generally numerous from chaetiger 19. Fully formed aristate chaeta ( Figure 45 View FIGURES 43 – 50 a, b) with truncate hook-like tufted knob at base of plumose arista (arista easily detached). A ‘beard’ of long hairs occurs below knob, where chaetal shaft narrows. In frontal view, knob appears as rounded button above a narrowing shaft and below long plumose arista ( Figure 46 View FIGURES 43 – 50 ). Initially 7–8 aristate chaetae in each ramus, decreasing to 6–7 in median chaetigers.

In posterior third of body (around chaetigers 60–70 on larger specimens), dorsalmost two aristate chaetae in notopodia gradually transition into slightly sigmoidal spines with gently curved tips, some almost straight; uppermost spine thinnest ( Figures 47, 48 View FIGURES 43 – 50 ). Notopodial spines accompanied by 5 aristate, 3 sympodial and small number of plumose chaetae. Corresponding neuropodia with 6–7 aristate, 4–5 sympodial, and more abundant plumose chaetae. In following segments (around chaetigers 75–80) notopodial spines increase to 4– 5 per notopodium, and other chaetae become less numerous—comprising 2–3 aristate and 2 sympodial chaetae accompanied inferiorly by sparse bundle of smooth capillaries. Any remaining plumose chaetae increasingly denuded of long hairs. Neuropodia with 5–7 aristate and 3–4 sympodial chaetae; plumose chaetae becoming progressively smoother with only 4–5 inferior chaetae retaining some sparse long hairs.

In posterior sixth of body (from about chaetiger 80-85), aristate chaetae and sympodial chaetae decrease to only 1 per notopodium, accompanied by 5–6 smooth capillaries. Neuropodia with 2–3 aristate, 1–2 sympodial and 4–5 smooth capillary chaetae. Sparsely haired plumose chaetae rare in both rami. Robust sigmoidal notopodial spines accompanied by small posterior row of slender, smooth needle-like, spines with slightly curved tips ( Figure 49 View FIGURES 43 – 50 ) from about chaetiger 75–80; initially 4–5 slender spines, later increasing to about 12 in bundle. Number of sigmoidal spines increases to 6 or 7 on posteriormost chaetigers; aristate and sympodial chaetae absent. Neuropodia from about chaetiger 80–85 also with spines; initially 2 ventral spines, increasing to 4 in number, accompanying 4–5 smooth capillaries and 2 (decreasing to 0) aristate chaetae. Neuropodial spines very similar to robust sigmoidal notopodial spines ( Figure 50 View FIGURES 43 – 50 ), but maximally only a little thicker than superiormost of these.

Colour. In life, anterior orange-red and yellow, median and posterior regions brown. Preserved specimens in alcohol, white.

Etymology. The specific name " perequensis " refers to the name of the creek near the type locality in Paranaguá Bay. "Perequê" comes from the indigenous language Tupy-guarany, and means the entrance of a place for feeding and breeding of fishes.

Occurrence. Muddy sand, intertidal flat and shallow sublittoral (to 15 m) Paranaguá Bay, southeast coast of Brazil.

Remarks. Poecilochaetus perequensis sp. nov. resembles P. australis Nonato, 1963 , the only species previously reported to Brazilian coast, in the presence of aristate chaetae and ampullaceous postchaetal lobe on chaetigers 7–13. However, P. perequensis differs markedly in having both large and slender, smooth, curved spines in posterior notopodia, rather than only slender barbed ones. In addition, the lobes of the nuchal organ are more similar in length in P. perequensis . In P. australis they are more disparate, the median nuchal organ reaching to chaetiger 10, while the lateral ones are vestigial. The aristate chaetae are quite different in the 2 species. Aristate chaetae in P. perequensis have a lateral tufted hook-like projecting knob, surmounted by a plumose arista, as found in P. serpens honiarae , P. trilobatus , and P. koshikiensis . Should P. gallardoi Pilato & Cantone, 1976 prove to be the posterior end of P. paratropicus Gallardo, 1968 from Vietnam (see Mackie 1990), then P. paratropicus would possess this form of aristate chaeta too (see Table 1). Eibye-Jacobsen (2006) identified P. paratropicus from Thailand and coded the species as having a dorsal chitinous plate on chaetiger 9, and posterior notopodia with both curved hooks and straight (or weakly curved) spines. The first feature is a new observation, the second consistent with the synonymy of P. gallardoi , however Eibye-Jacobsen (2006) did not consider the presence or absence of aristate chaetae in his cladistic analyses.

All 6 taxa, including ( P. perequensis ) have ampullaceous lobes on chaetigers 7–13, but the presence of branchiae readily distinguishes P. serpens , P. serpens honiarae and P. trilobatus from the others. Poecilochaetus koshikiensis Miura, 1988 has reduced, discoid, lateral nuchal lobes—rather than the short (reaching chaetiger 2 or 3), medium (reaching chaetiger 4 or 5) or long (reaching chaetiger 6 or beyond) lobes of the other 5 taxa. Poecilochaetus perequensis appears closest to P. paratropicus (including P. gallardoi ). Both have plumose chaetae from chaetiger 17, and posterior notopodial hooks and spines. Nevertheless, the two species are easily separated by the fact that the posterior notopodial hooks and spines are relatively slender in P. p e re - quensis compared to the robust forms found in P. paratropicus . Furthermore, aristate chaetae are always present by chaetiger 19 (18-20) in P. perequensis , but are absent from at least the first 25 chaetigers in P. p a r a - tropicus .

The distinctive sigmoidal notopodial hooks of Poecilochaetus perequensis are very similar to those found posteriorly in P. fauchaldi Pilato & Cantone, 1976 . The Mediterranean species differs in having discoid lateral nuchal organs and robust posterior notopodial spines, and also lacks aristate chaetae.