Exogone gigas, Paresque, Karla, Fukuda, Marcelo Veronesi & Nogueira, João Miguel De Matos, 2014

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 : 525-530

Exogone gigas sp. n.

( Figures 14–15 , Table 1)

Material examined. Type series. (Morphological features of specimens from type-series provided in Table 1). Holotype: Project ‘ HABITATS’: State of Rio de Janeiro, 22°11'56''S 40º32'15''W, 68 m, soft bottom ( MZUSP 1271), coll. 15 March 2009. Paratypes: Project ‘ HABITATS ’: State of Rio de Janeiro, 22°11'56''S 40º32'15''W, 68 m, soft bottom, 15 March 2009. Paratype 1 ( MZUSP 1272), paratype 2 ( MZUSP 1273), paratype 3 ( MZUSP 1274), paratype 4 ( ZUEC 13534), paratype 5 ( ZUEC 13533), paratype 6 ( ZUEC 13532), paratype 7 ( MZUSP 2083), paratype 8 ( MZUSP 2084), paratype 9 ( MNCN 16.01/14629), paratype 10 ( MNCN 16.01/14630). “Project ‘ HABITATS ’: State of Rio de Janeiro, Campos Basin, Van Veen grab; 21º9'9.813"S 40º16'7.837"W, 103 m: 2 specimens ( MZUSP 1293), coll. 21 July 2009; 21º10'16.281"S 40º45'58.437"W, 21 m: 10 specimens ( MZUSP 1299), coll. 22 July 2009; 21º11'0.342"S 40º28'28.313"W, 26 m: 9 specimens ( MZUSP 1292), coll. 21 July 2009; 21º17'25.438"S 40º54'6.865"W, 16 m: 1 specimen ( MZUSP 1291), coll. 18 July 2009; 21º17' 53.022"S 40º 30'59.297"W, 30 m: 2 specimens ( MZUSP 1303), coll. 22 July 2009; 21º21'21.471"S 40º52'9.225"W, 20 m: 2 specimens ( MZUSP 1295), coll. 23 July 2009; 21º24' 43.527"S 40º 25'20.695"W, 32 m: 1 specimen ( MZUSP 1304), coll. 20 July 2009; 21º28'2.200"S 40º56'21.516"W, 17 m: 7 specimens ( MZUSP 1294), coll. 20 July 2009; 21º33'54.232"S 40º42'55.434"W, 23 m: 2 specimens ( MZUSP 1300), coll. 20 July 2009; 21º34' 13.655"S 40º 25'31.571"W, 28 m: 12 specimens ( MZUSP 1305), coll. 23 July 2009; 21º40'23.730"S 40º58'23.765"W, 18 m: 3 specimens ( MZUSP 1296), coll. 19 July 2009; 21º47'15.563"S 40º57'34.882"W, 16 m: 2 specimens ( MZUSP 1297), coll. 18 July 2009; 21º50' 21.049"S 40º 31'37.376"W, 28 m: 1 specimen ( MZUSP 1302), coll. 23 July 2009; 21º57'16.013"S 40º37'59.948"W, 27 m: 9 specimens ( MZUSP 1283), coll. 26 February 2009; 22º1'7.705"S 40º31'53.782"W, 49 m: 1 specimen ( MZUSP 1301), coll. 24 July 2009; 22º3'41.155"S 40º24'9.910"W, 56 m: 42 specimens ( MZUSP 1284), coll. 25 February 2009; 22º6'40.471"S 40º54'46.350"W, 30 m: 9 specimens ( MZUSP 1288), coll. 17 July 2009; 22º6'42.052"S 40º54'44.607"W, 29 m: 34 specimens ( MZUSP 1278), coll. 26 February 2009; 22º6'55.679"S 40º38'58.325"W, 53 m: 93 specimens ( MZUSP 1282), coll. 26 February 2009; 22º6'55.873"S 40º38'59.945"W, 53 m: 20 specimens ( MZUSP 1290), coll. 17 July 2009; 22º7'43.309"S 40º18'46.483"W, 73 m: 3 specimens ( MZUSP 1285), coll. 24 February 2009; 22º11'30.609"S 40º55'24.468"W, 44 m: 2 specimens ( MZUSP 1298), coll. 17 July 2009; 22º12'37.087"S 40º13'18.731"W, 99 m: 2 specimens ( MZUSP 1286), coll. 24 February 2009; 22º12'52.897"S 40º51'12.067"W, 52 m: 82 specimens ( MZUSP 1280), coll. 26 February 2009; 22º12'52.906"S 40º51'13.559"W, 52 m: 14 specimens ( MZUSP 1289), coll. 17 July 2009; 22º17'25.519"S 40º6'36.262"W, 143 m: 2 specimens ( MZUSP 1287), coll. 24 February 2009; 22º18'50.070"S 41º21'35.068"W, 28 m: 18 specimens ( MZUSP 1277), coll. 27 February 2009; 22º19'27,600" S 40º37'25,122"W, 75 m: 14 specimens ( MZUSP 1281), coll. 15 March 2009; 22º37'35.330"S 41º21'51.788"W, 53 m: 2 specimens ( MZUSP 1276), coll.

27 February 2009; 22º52'1.951"S 40º57'28.983"W, 92 m: 1 specimen ( MZUSP 1279), coll. 22 February 2009; 23º10'4.258"S 41º3'6.679"W, 105 m: 1 specimen ( MZUSP 1275), coll. 21 February 2009. Project ‘ BioPol-NE ’: State of Paraíba: João Pessoa, Praia de Cabo Branco (06°57.761'S 34°50.556'W), intertidal: 7 specimens ( MZUSP 1346), coll. 0 2 February 2010. Conde, Praia de Tabatinga (07°19.297'S 34°47.862'W), intertidal: 1 specimen ( MZUSP 1347), coll. 0 1 September 2011.

Additional material examined. Exogone multisetosa Friedrich, 1956 . Peru, Lima – holotype ( ZMH P- 15371), 2 paratypes ( ZMH P- 15372), coll. 22 June 1952, det. Friedrich, 1956.

Description. Body thin, elongated, 8–11 (10) mm long and 0.20–0.35 (0.27) mm wide, with up to 80 (78) chaetigers. Palps triangular, distally rounded, totally fused, with a conspicuous line of fusion and distal notch ( Figs 14 A, 15A). Prostomium ovate, shorter than palps, two pairs of eyes in trapezoidal arrangement; anterior eyespots absent; median antenna inserted between anterior pair of eyes, elongated, almost reaching tip of palps ( Fig. 14 A); lateral antennae small, digitiform, inserted slightly anteriorly to median antenna ( Figs 14 A, 15A). Ciliated nuchal organs dorsolaterally between prostomium and peristomium ( Fig. 15 A, C). Peristomium shorter than following chaetigers; peristomial cirri ovate, similar to lateral antennae but smaller, about 2/3 as long as lateral antennae ( Fig. 14 A). Dorsal cirri with shape similar to lateral antennae but slightly smaller, absent on chaetiger 2. Ventral cirri inserted at bases of parapodia, shorter than parapodial lobes. Parapodial lobes conical; anterior parapodia with 1–3 (1–2) spiniger-like chaetae and 4–10 (6–9) falcigers each, midbody parapodia with 1–2 (1) spiniger-like chaetae and 2–4 (3–4) falcigers, posterior parapodia with single spiniger-like chaeta and 2–3 (2) falcigers each; spinigerlike chaetae of chaetiger 2 with thick shafts, subdistally provided with triangular process with minute spines ( Figs 14 B, 15D–E); shafts of spiniger-like chaetae of remaining chaetigers without triangular process, subdistally spinulated ( Figs 14 C–E, 15F, I, L, P); blades of spiniger-like chaetae unidentate ( Figs 14 E, 15G, K) to indistinctly bifid ( Fig. 14 B–D), 50–40 (47–42) µm long on anterior parapodia, 45–22 (45–25) µm long on midbody, 35–17 (25–17) on posterior parapodia. Shafts of falcigers subdistally enlarged and spinulated; blades of falcigers spinulated and bidentate ( Figs 14 C–E, 15E–F, H–I, P), spinulation of blades and difference of size between teeth more evident on anterior parapodia; blades 6–11 (7–10) µm long on anterior parapodia, 4–9 (4–8) µm on midbody, and 3–6 (4–6) µm long on posterior parapodia. Dorsal simple chaetae usually beginning from chaetiger 6–11 (11), sigmoid, subdistally spinulated, with acute tip ( Figs 14 F, 15J), stouter on posterior chaetigers ( Fig. 14 G). Ventral simple chaetae present only on posterior chaetigers, sigmoid, bidentate, subdistal tooth larger ( Figs 14 H, 15M, O). Anterior parapodia with up to three aciculae each, two slightly bent subdistally, with inflated, apparently hollow tip, third acicula distally bent at almost 90° ( Fig. 14 I); from midbody onwards, single acicula per parapodium, of the first type ( Fig. 14 J). Pygidium semicircular with pair of thin, elongate anal cirri. Pharynx through 3.5–5.5 (5.5) segments, tooth at anterior border; anterior margin of pharynx surrounded by papillae and fringe of cilia ( Fig. 15 B); proventricle extending for 3.5–5 (3.5) chaetigers, with 25–27 (26) rows of muscle cells.

Remarks. This species is characterized by having a triangular process with minute spines on the shafts of spiniger-like chaetae of chaetiger 2, a large median antenna, and by lacking dorsal cirri on chaetiger 2. Exogone lourei , E. rostrata , E. longicornis , E. multisetosa and E. arenosa are the species most similar to E. gigas sp. n., sharing with it the presence of a triangular process on the shafts of the spiniger-like chaetae in certain anterior chaetigers.

Exogone lourei differs from E. gigas sp. n. by having dorsal cirri on chaetiger 2, a triangular process on the shafts of spiniger-like chaetae of chaetiger 1 and 2, a pharynx through 6–7 segments, and a proventricle extending for ca. 3 segments, with 23 rows of muscle cells, while E. gigas sp. n. lacks dorsal cirri on chaetiger 2, has a triangular process on the shafts of spiniger-like chaetae only on chaetiger 2, pharynx extending through 3.5–5.5 segments, and proventricle through 3.5–5 segments, with 25–27 rows of muscle-cells.

Exogone rostrata is similar to E. gigas sp. n. by having median antenna longer than lateral ones, and pharynx through about 5 chaetigers. However, E. rostrata differs from E. gigas sp. n. by being a shorter species, with up to 7 mm in length and 47 chaetigers vs. 1–10 mm and 80 chaetigers as in E. gigas sp. n.. Furthermore, E. rostrata has dorsal cirri on chaetiger 2; spiniger-like chaetae with spinulated triangular process on chaetiger 1 only, and with shorter, distally bifid blades, ca. 20 µm long; two aciculae per parapodium on anterior body; and proventricle shorter, through about 3 segments. On the other hand, E. gigas sp. n. has spiniger-like chaetae with smooth triangular process, on chaetiger 2 only, and longer, unidentate to indistinctly bifid blades, 17–50 µm long; three aciculae per parapodium on anterior body; and proventricle through 3.5–5 segments.

TABLE 1. Morphological features of the type series of Exogone gigas sp. n.

Exogone longicornis also has dorsal cirri on chaetiger 2 and a triangular process is present on the shafts of spiniger-like chaetae of chaetigers 1 and 2 ( San Martín 2005). In addition, E. longicornis has shorter blades of spiniger-like chaetae throughout, 26 µm, 26 µm, and 20 µm long on anterior, midbody and posterior chaetigers, respectively, and a proventricle with 33–38 rows of muscle cells. In contrast, E. gigas sp. n. has blades of spinigerlike chaetae 30–50 µm, 22–45 µm, and 17–35 µm long on anterior, midbody and posterior chaetigers, and a proventricle with 25–27 rows of muscle-cells.

Exogone multisetosa is a smaller species, the holotype, with 41 chaetigers, was described from the Pacific Ocean (Lima, Peru) and can be differentiated from E. gigas sp. n. by having a shorter, squared triangular process on spiniger-like chaetae of chaetiger 2, ventral simple chaetae with acute tip, and shorter proventricle, through 2.5–3 segments. Exogone arenosa differs from E. gigas sp. n. by having dorsal cirri on chaetiger 2, pharynx through 7 segments, and proventricle with 27–36 rows of muscle cells.

Etymology. The epithet gigas is derived from Latin, meaning "giant", and refers to the length of this species, which is the longest known for this genus.

Distribution. Atlantic Ocean: Brazil (Rio de Janeiro and São Paulo). From the intertidal zone to ca. 143 m.

Figures

FIGURE 14. Exogone gigas sp. n. (A) Anterior end, left dorso-lateral view; (B) spiniger-like chaeta, chaetiger 2; (C) compound chaetae, anterior body; (D) compound chaetae, midbody; (E) compound chaetae, posterior body; (F) dorsal simple chaeta, anterior body; (G) dorsal simple chaeta, posterior body; (H) ventral simple chaeta, posterior body; (I) aciculae, anterior body; (J) acicula, posterior body. Scale bars: A, 200 Μm; B – J, 10 Μm.

FIGURE 15. Exogone gigas sp. n., SEM. (A) Anterior end, dorsal view; (B) pharynx, frontal view; (C) detail of one nuchal organ; (D) shaft of spiniger-like chaeta, chaetiger 2; (E) compound chaetae, chaetiger 2; (F) chaetae, chaetiger 3; (G) tip of spiniger-like chaeta, chaetiger 2; (H) falciger, chaetiger 2; (I) compound chaetae, midbody; (J) dorsal simple chaeta, midbody; (K) tip of spiniger-like chaeta, midbody; (L) spiniger-like chaeta, midbody; (M) ventral simple chaeta, midbody; (N) tip of spiniger-like chaeta, posterior body; (O) ventral simple chaeta, posterior body; (P) compound chaetae, posterior body. no — nuchal organ. Scale bars: A, 100 Μm; B, 50 Μm; C, 20 Μm; D, H, 5 Μm; E, G, N, 2 Μm; F, I – J, L, M, O – P, 10 Μm; K, 1 Μm.