Exogone arenosa Perkins, 1981

Paresque, Karla, Fukuda, Marcelo Veronesi & Nogueira, João Miguel De Matos, 2014, The genus Exogone (Polychaeta: Syllidae) from the Brazilian coast, with the description of a new species, Zootaxa 3790 (4), pp. 501-533 : 522-525

Exogone arenosa Perkins, 1981

( Figures 12–13 )

Exogone arenosa Perkins, 1981: 1094 –1097, figs 5g –j, 6; Lana 1984: 66 –67, figs 55–56; Sovierzoski 1999: 61 –62, fig. 11.? Exogone dispar . Temperini 1981: 20 –21.

Exogone (Exogone) arenosa . Fukuda 2010: 118 –121, fig. 32.

Material examined. Project ‘ REVIZEE ’: State of Rio de Janeiro: 23°08.07'S 41°00.84'W, 110 m: 1 specimen, coll. 28 February 1998; 23°20.0'S 41°22.0'W, 110 m: 5 specimens, coll. 28 February 1998. Project ‘ BIOTA ’: State of São Paulo: São Sebastião, sublittoral, 23°56'373''S 45°27'080''W, 44.6 m: 3 specimens, coll. 15 December 2001. Project ‘ HABITATS ’: State of Rio de Janeiro (Campos Basin), Van Veen grab; 21°22'58"S 40°19'41"W, 53 m: 7 specimens, coll. 0 5 March 2009, 1 specimen, coll. 21 July 2009; 21°28'2"S 40°56'20"W, 16 m: 1 specimen, coll. 10 March 2009; 21°42'37"S 40°8'59"W, 147 m: 1 specimen, coll. 0 9 March 2009; 21°43'10"S 40°11'30"W, 73 m: 7 specimens, coll. 0 9 March 2009; 22°3'45"S 40°9'59"W, 75 m: 3 specimens, coll. 25 February 2009; 22°6'42"S 40°54'45"W, 29 m: 2 specimens, coll. 26 February 2009; 22°17'42"S 40°26'59"W, 104 m: 4 specimens, coll. 23 February 2009; 22°19'32.134"S 40°37'19.109"W, 75 m: 1 specimen ( MZUSP 2062), coll. 15 March 2009; 23°10'4"S 41°3'6"W, 105 m: 1 specimen, coll. 21 February 2009; 23°11'30"S 41°0'48"W, 150 m: 2 specimens, coll. 21 February 2009. Project ‘ BioPol-NE ’: State of Paraíba: Conde, Praia de Tabatinga (07º19'S 34º47'W), intertidal: 1 specimen ( MZUSP 2063), coll. 0 1 September 2011; Praia de Tambaba (07°21'S 34°47'W), intertidal: 1 specimen ( MZUSP 2064), coll. 30 August 2011. João Pessoa, Praia de Cabo Branco (07o08'S 34o47'W), intertidal: 1 specimen ( MZUSP 1335), coll. 0 9 February 2009, 5 specimens ( MZUSP 1336), coll. 0 2 February 2010. State of Pernambuco, Ilha de Itamaracá, Recifes de Itamaracá (07°43.944'S 34°49.200'W), 1 m: 3 specimens ( MZUSP 2065), coll. 15 December 2012.

Additional material examined. Exogone arenosa . USA, Florida, St. Lucile County, Hutchinson Island (27°22.08'N 80°13.48'W), 10 m: paratype ( ZMH P- 16389), leg. & det. T. Perkins.

Description. Body thin, elongated, longest specimens ca. 7.7 mm long and 0.7 mm wide, with up to 48 chaetigers. Palps triangular, distally rounded, almost totally fused, with conspicuous line of fusion and distal notch ( Figs 12 A, 13A). Prostomium pentagonal to ovate, about half length of palps, with two pairs of eyes in trapezoidal arrangement, anterior eyespots absent; median antenna inserted between anterior pair of eyes, elongated, usually reaching tip of palps or slightly shorter, subdistally inflated, with thin tip ( Fig. 12 A); lateral antennae digitiform, inserted slightly anteriorly to median antenna, ovate to papilliform, ca. 1/4 length of median antenna ( Fig. 12 A). Peristomium shorter than following chaetigers; peristomial cirri similar to lateral antennae but smaller, about half length of lateral antennae ( Figs 12 A, 13A). Dorsal cirri ovate, slightly larger than peristomial cirri, present on all chaetigers ( Fig. 13 A, D).Ventral cirri similar to dorsal cirri but smaller, ca. ¾ length of parapodial lobes. Parapodial lobes conical ( Fig. 13 A, D); anterior parapodia with 1–2 spiniger-like chaetae and 4–8 falcigers each, midbody with single spiniger-like chaeta and 4–8 falcigers each, posterior parapodia with single spiniger-like chaeta and 2–3 falcigers each. Spiniger-like chaetae of chaetiger 2 with thick shafts subdistally provided with triangular process ( Figs 12 D, 13E–F); shafts of spiniger-like chaetae of remaining parapodia enlarged, subdistally spinulated ( Fig. 12 F, I, N); blades of spiniger-like chaetae spinulated, with short spines, blades distally bifid, with minute, inconspicuous teeth ( Fig. 12 D, F, I, N; 13H); blades ca. 60–25 µm long on anterior parapodia, 56–25 µm long on midbody and 25–15 µm long in posterior parapodia. Shafts of falcigers subdistally enlarged and spinulated; blades of anterior falcigers more spinulated, spinulation inconspicuous in posterior falcigers; blades bidentate, subdistal tooth larger ( Figs 12 E, J, O, 13E–G, I), 15–7 µm long on anterior parapodia, 10–5 µm on midbody and 7–3 µm long on posterior parapodia. Dorsal simple chaetae usually present on all chaetigers, sigmoid, subdistally spinulated, with acute tip ( Figs 12 C, H, L, 13E, G, J–K), progressively stouter posteriorwards. Ventral simple chaetae present only on posterior chaetigers, sigmoid, bidentate, subdistal tooth larger ( Figs 12 M, 13L). Anterior parapodia with up to three aciculae each, two straight with acute tip, remaining acicula slightly bent subdistally, with inflated tip ( Fig. 12 B); each midbody parapodium with two aciculae, one of each type ( Fig. 12 G), posterior parapodia with one acicula each, of the second type ( Fig. 12 K). Pygidium with thin, elongate pair of anal cirri. Pharynx through seven segments; tooth at anterior border; anterior margin of pharynx surrounded by 10 papillae with fringe of cilia ( Fig. 13 B–C); proventricle extending for 3.5–7 chaetigers, with 27–36 rows of muscle cells.

Remarks. Exogone arenosa is similar to E. longicornis Westheide, 1974 and E. lourei by having the median antenna longer than the lateral ones, dorsal cirri present on all chaetigers, and the triangular process on the shafts of spiniger-like chaetae of chaetiger 2.

Exogone longicornis differs from E. arenosa by having triangular processes on the shafts of spiniger-like chaetae of chaetigers 1 and 2, and of different morphology, with larger and stouter tips; spiniger-like chaetae and falcigers with shorter blades, blades of spiniger-like chaetae ca. 26 m long on anterior and midbody parapodia, 20 µm on posterior chaetigers, vs. 60–25 µm, 56–25 µm, and 25–15 µm on anterior, midbody and posterior chaetigers of E. arenosa , respectively; falciger blades 5–4 µm long in E. longicornis , while falcigers of E. arenosa are 15–7 µm, 10–5 µm and 7–3 µm long on anterior, mid- and posterior body chaetigers ( San Martín 2005), respectively. Exogone lourei also differs from E. arenosa by having triangular processes on the shafts of the spiniger-like chaetae of chaetigers 1 and 2, and a proventricle with ca. 23 rows of muscle cells (27–36 in E. arenosa ) ( San Martín 2005). Exogone arenosa shares some characters with E. rolani and E. dispar , as discussed above (see 'Remarks' for these species).

The Brazilian specimens examined match the original description ( Perkins 1981), except for the pronounced spine on the dorsal simple chaetae carefully described by Perkins (1981) was not visible in our material, even under SEM. However, in the paratypes examined the presence of this spine could not be verified for all dorsal simple chaetae of the specimens.

Type locality. USA, Florida, Hutchingson Island (Atlantic Ocean).

Distribution. Atlantic Ocean: USA (Florida), Brazil (Paraíba, São Paulo, Paraná); Caribbean Sea: Cuba, Panamá, and Venezuela. From the intertidal zone to ca. 150 m.

Figures

FIGURE 12. Exogone arenosa. (A) Anterior body, dorsal view; (B) aciculae, anterior body; (C) dorsal simple chaeta, anterior body; (D) spiniger-like chaeta, chaetiger 2; (E) falcigers, anterior body; (F) spiniger-like chaeta, anterior body; (G) aciculae, midbody; (H) dorsal simple chaeta, midbody; (I) spiniger-like chaeta, midbody; (J) falcigers, midbody; (K) acicula, posterior body; (L) dorsal simple chaeta, posterior body; (M) ventral simple chaeta, posterior body; (N) spiniger-like chaeta, posterior body; (O) falcigers, posterior body. Scale bars: A, 0.3 mm; B – O, 10 Μm.

FIGURE 13. Exogone arenosa, SEM. (A) Anterior end, dorsal view; (B) pharynx, frontal view; (C) detail of pharynx, showing the ciliated border; (D) midbody chaetigers, dorsal view; (E) chaetae, anterior parapodium; (F) falciger and detail of triangular process of spiniger-like chaeta of chaetiger 2; (G) chaetae, midbody parapodium; (H) spiniger-like chaeta, midbody parapodium; (I) falciger, posterior body; (J) (K) dorsal simple chaetae, anterior and posterior body, respectively; (L) ventral simple chaeta, posterior body. la — lateral antennae; ma — median antenna; pa — palp; pha — pharynx; pr — prostomium. Scale bars: A, D, 50 Μm; B, 20 Μm; C, K, 5 Μm; E, G, H, 10 Μm; F, I, J, L, 2 Μm.