Exogone (Exogone) arrakatarkoola, Guillermo San Martin, 2005

Guillermo San Martin, 2005, Exogoninae (Polychaeta: Syllidae) from Australia With the Description of a New Genus and Twenty-two New Species, Records of the Australian Museum 57, pp. 39-152 : 133-134

Exogone (Exogone) arrakatarkoola n.sp.

Fig. 82A–L

Material examined. AUSTRALIA: QUEENSLAND. HOLOTYPE: AM W26364, lagoon at south end of Lizard Island, 250 m ESE of Palfrey Island, 14°40'S 145°28'E, very fine sediment, 12 m, C. Short & A.R. Jones, 12 Oct 1978. PARATYPES: 4 specimens, AM W26365, 100 m off Mangrove Beach, Lizard Island, 14°40'S 145°28'E, coarse to medium sediment, 3 m, C. Short & A.R. Jones, 13 Oct 1978. PARATYPES: 4 specimens, AM W26366, 100 m off Mangrove Beach, Lizard Island, 14°40'S 145°28'E, medium sediment, 3 m, C. Short & A.R. Jones, 13 Oct 1978. PARATYPES: 3 specimens, AM W26367, 100 m off Mangrove Beach, Lizard Island, 14°40'S 145°28'E, medium sediment, 3 m, C. Short & A.R. Jones, 13 Oct 1978. PARATYPE: 1 specimen, AM W26368, 100 m off east end of Mangrove Beach, Lizard Island, 14°40'S 145°28'E, 3.6 m, C. Short & A.R. Jones, 11 Oct 1978. PARATYPE: 1 specimen, AM W26369, 100 m off east end of Mangrove Beach, Lizard Island, 14°40'S 145°28'E, 3.6 m, C. Short & A.R. Jones, 11 Oct 1978. PARATYPES: 4 specimens, AM W26370, 100 m off Mangrove Beach, south end of Lizard Island, 14°40'S 145°28'E, medium sediment, 3 m, C. Short & A.R. Jones, 13 Oct 1978. PARATYPES: 4 specimens, AM W26371, 400 m off Chinamans Ridge, Lizard Island, 14°40'S 145°28'E, 12 m, C. Short & A.R. Jones, 13 Oct 1978. PARATYPES: 2 specimens, AM W26372, 100 m off Mangrove Beach, south end of Lizard Island, 14°40'S 145°28'E, coarse to medium sediment, 3 m, C. Short & A.R. Jones, 13 Oct 1978. PARATYPES: 5 specimens, AM W26373, 100 m off Mangrove Beach, south end of Lizard Island, 14°40'S 145°28'E, medium sediment, 3 m, C. Short & A.R. Jones, 13 Oct 1978. 2 specimens, AM W26559, Halifax Bay, north of Townsville, 19°9'S 146°37'E, 5 m, QN, Jan 1977. 18 specimens, AM W26560, Halifax Bay, north of Townsville, 19°10'S 146°44'E, 5 m, QN, Jan 1977. 1 specimen, AM W26573, Halifax Bay, north of Townsville, 19°10'S 146°44'E, 5 m, QN, July 1977. 11 specimens, AM W26578, Halifax Bay, north of Townsville, 19°10'S 146°44'E, 5 m, QN, July 1977. 4 specimens, AM W26579, Halifax Bay, north of Townsville, 19°10'S 146°37'E, 5 m, QN, Jan 1977. 2 specimens, AM W26583, Halifax Bay, north of Townsville, 19°10'S 146°38'E, 5 m, QN, July 1977. 1 specimen, AM W26793, 3 m from coral bommie in lagoon at south end of Lizard Island, 14°40'S 145°28'E, coarse to medium sand, 3 m, A. Jones and C. Short, 13 Oct 1978. 1 specimen on SEM stub, AM W26891, Hinchinbrook Channel, 18°20'S 146°4'E, tidal mud- and sandflats, S. Dittmann, 14 Oct 1989.

Description. Body long, slender, filiform, 3.8–4 mm long, 0.2 mm wide, 40 chaetigers. Prostomium oval to rectangular, about 2.5 times wider than long; 4 large eyes in trapezoidal arrangement, anterior pair slightly larger than posterior pair; antennae located close to each other, between anterior eyes (Fig. 82A); median antenna cylindrical, shorter than prostomium, lateral antennae shorter, slightly more than ½ the length of median antenna (Fig. 82A). Palps broad, fused along their length, relatively short, slightly longer than prostomium. Peristomium distinct; tentacular cirri small, papilliform. Dorsal cirri longer than tentacular cirri, similar in length to lateral antennae, slightly pyriform (Fig. 82A), present on all segments. Anteriormost 2–3 parapodia each with about 8 compound chaetae, heterogomph, with long subdistal spines on shafts, and falcigerous blades, 1–2 dorsalmost chaetae with blades provided with indistinct distal tooth and long subdistal tooth, moderately long marginal spines and about 12–13 µm long, remaining compound chaetae with blades slightly shorter, 11–10 µm long, with shorter marginal spines and distal tooth slightly longer than those of dorsalmost ones (Fig. 82C). On parapodia of following 3–5 segments dorsalmost 1–2 compound chaetae have slightly elongate blades, about 15 µm long, with moderately long marginal spines; the remaining 6–7 compound chaetae with blades similar to those of anteriormost parapodia but slightly longer, about 12 µm long (Fig. 82D). Progressively posteriorly, 1–2 dorsalmost elongate falcigers transformed to spiniger-like chaetae, with spinose shafts, unidentate, filiform blades, provided with long marginal spines (Fig. 82F), blades about 34 µm long in midbody; remaining falcigers similar to those of anterior parapodia, but shorter (Fig. 82G), blades about 10 µm above, 8 µm below, numbering 3 on midbody segments. Posterior parapodia each with 1 compound spiniger-like chaetae, with filiform, nearly smooth blade (Fig. 82I), 19 µm long, and 2, sometimes 3, falcigers, with nearly smooth shafts and short, smooth blades, about 5 µm long (Fig. 82J). Dorsal simple chaetae from anterior parapodia, sometimes from chaetiger 1, with rounded tips and finely spinulose subterminally (Fig. 82E), thicker posteriorly (Fig. 82H). Ventral simple chaetae on posterior parapodia, sigmoid, smooth, with small distal tooth and longer subdistal tooth (Fig. 82K). Pharynx long, through about 5–6 segments; pharyngeal tooth located on anterior rim, surrounded by 10 soft papillae and a dense crown of long cilia (Fig. 82B). Proventricle similar in length to pharynx, through about 4–5 segments, with 32 muscle cell rows. Pygidium with 2 long anal cirri.

Remarks. Exogone (E.) arrakatarkoola n.sp. is characterized by the progressive elongation of blades of 1 or 2 dorsalmost compound chaetae of anterior parapodia to spiniger-like blades. Exogone (E.) naidina and E. (E.) goorapuranga also lack spiniger-like chaetae on anteriormost parapodia but Exogone (E.) arrakatarkoola has a much longer proventricle than either of these two species, lacks compound chaetae with modified blades on anteriormost parapodia, characteristic of Exogone (E.) naidina , and long spines on shafts of compound chaetae, present in E. (E.) goorapuranga .

Distribution. Australia (Queensland).

Habitat. Interstitial in fine to coarse sediment.

Etymology. The specific name is derived from a combination of two Aboriginal words, arkoola, meaning hair, and arrakata meaning mouth, in reference to the long cilia or “hairs” on the pharynx opening.