Poecilochaetus polycirratus 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 : 54-61

Poecilochaetus polycirratus Santos & Mackie sp. nov.

Figures 1–25

Material examined. Encantadas Beach, Ilha do Mel, Paranaguá Bay (25°34.26’S, 48°18.98’W), low intertidal region. Holotype complete ( MCEM 1290) and 3 paratypes, all incomplete ( MCEM 1291).

Description. Only the holotype posteriorly complete, but in four fragments, mostly poorly preserved: anterior fragment with 108 chaetigers, 83 mm long and 3.5 mm wide including parapodia; median fragment with 69 chaetigers, 39 mm long; second median fragment with 132 chaetigers, 70 mm long; posterior fragment with 39 chaetigers, 11 mm long. Total length 159 mm for 348 chaetigers. Paratypes are 3 anterior fragments: 1. with 70 chaetigers, 52 mm long and 2.75 mm wide including parapodia; 2. with 57 chaetigers, 47 mm long and 2.75 mm wide; 3. not measured.

Prostomium small, subrectangular, longer than wide, anterior margin concave; positioned between notopodia of chaetiger 1. Two pairs of small subdermal black eyes; anterior pair reniform, other pair smaller and more rounded, set closer together near posterior margin of prostomium ( Figures 1, 2 ).

Peristomium small, collar-like surrounding prostomium laterally and giving rise to 3 nuchal lobes posteriorly. Medium lobe conspicuously longer, reaching further than chaetiger 3 (all distally incomplete). Lateral nuchal lobes short, discoid, and divergent, completely connected to basal region of median by well-developed membranes ( Figure 2 ). Palps missing from all specimens. Long, blunt, cylindrical facial tubercle from upper margin of mouth, just below prostomium.

Ventral surfaces of chaetigers 1–3 densely covered with small, red, rounded tubercles; those immediately surrounding mouth smallest. Ventrolateral surfaces of chaetigers 6 to 8 (or 9) and anterior faces of next 2 or 3 parapodia with similar conspicuous tuberculation ( Figure 7 ); other anterior body surfaces smooth. No chitinous plate on dorsum of chaetiger 9.

Chaetiger 1 large, directed forwards; neuropodial postchaetal lobes long, cirriform; notopodial lobes rudimentary, triangular. Neuropodial postchaetal lobes of chaetigers 2–6 short, lanceolate, basally swollen ( Figure 3–5 ); most notopodial lobes of similar size and shape, those of chaetigers 2 and 5 longer ( Figures 1, 4 ).

Ampullaceous postchaetal lobes on chaetigers 7–13. Swollen basal parts of ampullaceous lobes glandular, distal parts smooth and somewhat iridescent ( Figure 7 ).

Postchaetal lobes on chaetiger 14 similar to those on chaetiger 6 ( Figure 5 ). Over following 6–8 chaetigers distal parts of postchaetal lobes become narrower and more distinct from large swollen basal parts ( Figure 8 ). In mid-body region, postchaetal lobes become narrower, more lanceolate ( Figures 9, 10 ). Posteriorly, notopodial lobes become shorter than neuropodial ones ( Figure 11 ).

Interramal sensory papillae on chaetigers 1–5 and 10–17 ( Figure 4 ), lacking on chaetigers 6–9. On following segments, sensory organs sessile, evident as single small interramal pores. In posteriormost region, sensory organs slightly projecting as low papillae.

Multiple interramal cirri arise from anterior faces of parapodia from chaetigers 18 which persist for about one third of the body ( Figures 9, 10 ); up to 8–10 cirri observed.

Branchiae arise on posterior faces of notopodia from chaetiger 17 as single cirriform filaments. Number of filaments progressively increasing to 5 or 6 over following chaetigers and branchiae assume palmate form ( Figures 9, 10, 12 ). Branchiae absent from posterior third of body.

Pygidium with large oblique anus and three short ventral anal cirri ( Figure 13 ). Cirri distally tapered; paired cirri basally broader, somewhat pyriform, arising laterally just above more subulate unpaired one. Length ratio of superior to inferior cirri 1:1.

Chaetiger 1 with long, slender capillaries, finely hirsute in distal regions (hairs visible at x400 magnification), notochaetae longer; arranged fan-like in both rami forming cephalic cage. Neuropodia of chaetigers 2 and 3 with 4–5 slightly hirsute falcate hooks ( Figure 14 ); tips of 1 or 2 partially-formed replacement hooks evident superiorly. Several (4–6) short slender finely hirsute capillaries superior to fully formed emergent hooks in both chaetigers. Notopodia of same chaetigers with 2 types of chaetae, inferior finely hirsute and superior spinose capillaries. Following chaetigers also with finely hirsute capillaries, appearing smooth (Figure 15) or almost so at x400, and spinose capillaries ( Figure 16 ) in notopodia. Hirsute capillaries increasingly accompany spinose ones in superior parts of rami; neuropodia with only finely hirsute capillaries. From chaetiger 9 spinose chaetae appear inferiorly in neuropodia, and hirsute nature of capillaries becomes more obvious in both rami.

Chaetae markedly different from chaetiger 19; both rami superiorly and inferiorly with long, plumose capillaries ( Figure 18 ) in addition to spinose and hirsute capillaries. In the middle of each ramus occur 10–12 hirsute capillaries with conspicuous stiff hairs in their medial regions, replaced from chaetiger 20 by spinoseplumose chaetae ( Figure 17 ). By chaetiger 52, chaetae less abundant, particularly outer plumose ones.

In posterior chaetigers, tips of spinose-plumose chaetae become progressively smoother ( Figure 19 ). Four or five notopodial hooks on posteriormost 37 chaetigers, accompanied by several spines ( Figures 20, 21 ). Hooks long, slender, strongly curved, ancistroid ( Figures 24, 25 ); superiormost hook half size and thickness of others ( Figure 11 ). Hooks and spines accompanied by smooth tipped spinose-plumose chaetae ( Figure 19 ), sympodial chaetae ( Figure 23 ), and plumose ( Figure 18 ) and hirsute capillaries ( Figure 22 ).

Etymology. The specific name “ polycirratus ” with multiple cirri, refers to the numerous slender interramal cirri.

Remarks. In Poecilochaetus , 11 other taxa are known to have branchiae (Table 1): P. serpens Allen, 1904 , P. serpens honiarae Gibbs, 1971 , P. tropicus Okuda, 1935 , P. modestus Rullier, 1965 , P. exmouthensis Hartmann-Schröder, 1980 , P. clavatus Imajima, 1989 , P. tokyoensis Imajima, 1989 , P. trilobatus Imajima, 1989 , P. spinulosus Mackie, 1990 , P. tricirratus Mackie, 1990 and P. multibranchiatus León-González, 1992 . These species differ from each other variously in the number of ampullaceous postchaetal lobes, commencement of branchiae, number of branchial filaments, length and shape of nuchal organs, and presence and number of interramal cirri (Table 1).

Poecilochaetus polycirratus sp. nov., closely resembles P. m o d e s t u s from West Africa and P. tricirratus from Hong Kong (Table 1). All have nuchal organs with an elongate median lobe and discoid lateral lobes, and possess large ancistroid notopodial hooks in their posterior regions. The new species differs markedly from the others (categorized as group 2 by Mackie 1990) in possessing ampullaceous lobes on chaetigers 7– 13, not 7–11. Furthermore, the branchiae have up to 6 filaments, rather than only 1 or 2.

Posterior ancistroid notopodial hooks are found also in P. tropicus from the Palau Islands as redescribed by Imajima (1989) from an entire Japanese specimen. This species, like P. polycirratus , has ampullaceous lobes on chaetigers 7–13 and an elongate median nuchal lobe, but the branchiae are present as 2 separate filaments.

The new species possesses interramal cirri, a feature previously described only in P. tricirratus , P. japonicus Kitamori, 1965 and P. clavatus (including P. branchiatus ; Miura pers. comm.). However, the cirri are much more numerous (up to 10 against 1–3) in the new species (Table 1). The posterior notopodial chaetae of Kitamori’s species are not known. Poecilochaetus clavatus differs markedly in having ampullaceous lobes on chaetigers 7–10, straight notopodial spines, and 2 (rather than 3) anal cirri.

Poecilochaetus polycirratus sp. nov., is unusual in apparently lacking a chitinous plate on the dorsum of chaetiger 9. The plate was not observed on any of the 4 specimens available. It is considered to be consistently absent in Poecilochaetus species with heavily papillated body surfaces ( Mackie 1990: group 1; Eibye-Jacobsen 2006: papillate clade). In smooth-bodied forms, only P. bermudensis Hartman, 1965 has been recorded as lacking such a plate (see Pilato & Cantone 1976). No mention of the structure was made in the original descriptions of P. t ro p i c u s, P. vietnamita Gallardo, 1968 , P. modestus , P. japonicus , P. v i t j a z i Levenstein, 1962, and P. multibranchiatus . Confirmation of the presence or absence of the chitinous plate on chaetiger 9 would require re-examination of the type specimens in the first instance. It may be necessary also to examine additional material (including P. polycirratus ), preferably covering a range of specimen sizes, as it is possible that the plate may be lost or worn away on larger examples of some species.

Occurrence. Intertidal flat, muddy-sand, Paranaguá Bay, southeast coast of Brazil.

Figures

FIGURES 1 – 7. Poecilochaetus polycirratus sp. nov. 1. Holotype, dorsal view of anterior end, palps lacking; 2. detail of prostomium, dorsal view; 3. parapodium 3; 4. parapodium 5; 5. parapodium 6; 6. parapodium 7; 7. parapodium 10, sensory organ omitted. Chaetae omitted from all parapodia. All parapodia in anterior view. Scales. 1. 1.5 mm; 2. 1.0 mm, 4 – 7. 0.4 mm.

FIGURES 8 – 13. Poecilochaetus polycirratus sp. nov. 8. parapodium 20, anterior view; 9. parapodium 55, posterior view; 10. parapodium 69; 11. posterior parapodium; 12. dorsal view showing branchiae, chaetigers 63 – 65; 13. pygidium (holotype). Chaetae omitted from figures 8 to 10. All parapodia, except 55, in anterior view. Scales 8 - 11. 0.4 m; 12, 13. 0.2 mm.

FIGURES 14 – 25. Poecilochaetus polycirratus sp. nov. 14. neuropodial hook from chaetiger 2; 15. notopodial capillary from chaetiger 2; 16. spinose chaeta from chaetiger 2; 17. spinose-plumose from chaetiger 22; 18. plumose chaeta from chaetiger 21; 19. spinose-plumose from posterior chaetiger; 20. notopodial spine from posterior chaetiger; 21. notopodial spine from posterior chaetiger; 22. hirsute chaeta from posterior chaetiger; 23. sympodial chaeta from posterior chaetiger; 24. superiormost notopodial hook from posterior chaetiger; 25. notopodial hook from posterior chaetiger. Scales 100 µm.