Dialychone okudai, Nishi, Eijiroh, Tanaka, Katsuhiko, Tovar-Hernández, María Ana & Giangrande, Adriana, 2009

Nishi, Eijiroh, Tanaka, Katsuhiko, Tovar-Hernández, María Ana & Giangrande, Adriana, 2009, Dialychone, Jasmineira and Paradialychone (Annelida: Polychaeta: Sabellidae) from Japan and adjacent waters, including four new species descriptions, Zootaxa 2167, pp. 1-24 : 14-15

Dialychone okudai new species

Figures 8–9

Material examined. Type material: HOLOTYPE — CBM –ZW 1014, Aikap, Akkeshi, Hokkaido, rocky shore, July 0 1, 1995, by T. Kato. PARATYPES —NHM-ANEA.2009.15, Aikap, Akkeshi, Hokkaido, rocky shore, July 0 1, 1995, by T. Kato. ZIHU-3804, Aikap, Akkeshi, Hokkaido, rocky shore, July 0 1, 1995, Coll. T. Kato. USNM 1123950, Daikokujima, Akkeshi, Hokkaido, July 31, 2000, Coll. T. Kato. ECOSUR 0 0 92, Aikap, Akkeshi, Hokkaido, rocky shore, July 0 1, 1995, Coll. T. Kato. ZMUC-POL-2060, Oshoro, Hokkaido, Kabuto-iso, intertidal, June 12, 1998, Coll. T. Kato. SAMA E 3724, Oshoro, Hokkaido, Kabuto-iso, intertidal, June 12, 1998, Coll. T. Kato. KMHN-IvR- 500.418, Oshoro, Hokkaido, Kabuto-iso, intertidal, April 12, 1995, Coll. T. Kato.

Description Body cream colored in preserved specimen. Trunk cylindrical, abdomen flattened dorsoventrally. Body length: 25 mm in holotype, 10–25 in paratypes, width: 1.5–1.6 mm in holotype, 0.6–2.0 mm in paratypes. Tubes thin, membranous. Insertion of branchial lobes not exposed beyond collar ( Figures 8 A–B, 9A–C). Branchial crown length 5.0 mm in holotype, 4.0– 5.5 mm in paratypes. Nine pairs of radioles in holotype, 9–11 pairs in paratypes, connected for three quarters of length by membrane. Radioles with longest pinnules at three quarters of their length. Radiolar tips wide and short (0.6 mm versus 4.5 mm crown length) ( Figure 9 D). Radiolar skeleton with two rows of cells. Lateral flanges broad along the outer edges of radioles. Dorsal lips pointed, without radiolar appendages ( Figure 8 E). One to 4 pairs of short dorsal pinnular appendages united by web, basal-most usually longest ( Figure 8 E). Paired ventral lips short, broadly rounded. Two or three pairs of long ventral radiolar appendages, reaching one half radiole length. Anterior peristomial ring lobe triangular, distally entire, digitifom, visible beyond collar ( Figures 8 B, 9A–B). Anterior margin of collar with two v-shaped notches dorsally ( Figures 8 A, 9C), margin of collar entire lateral and ventral ( Figure 9 A–C). Ventral margin of collar higher than lateral and dorsal ( Figure 9 B). Mid-dorsal collar margin forms narrow gap ( Figures 8 A, 9C). Dorsal pockets well developed ( Figures 8 A, 9C). Ventral shield of collar swollen, horseshoe-shaped, 1.5 times wider than long; with an anterior curving belt translucent without staining or white when stained with methyl green ( Figures 8 B, 9A). Lateral white pad on anterior-lateral to dorsal area of collar ( Figure 8 C). Posterior peristomial ring collar 1.5 times longer than chaetiger l in lateral view. Post-chaetal glandular girdle encircling second chaetiger, uniformly narrow. Ventral thoracic shields absent ( Figures 8 B, 9A). First thoracic chaetiger with single bundle of long, narrow hooded chaetae. Subsequent thoracic segments each with three kinds of notochaetae: superior group of long hooded chaetae and inferior group of short hooded chaetae and paleate chaetae with long mucros ( Figures 8 D, 9G) and slender bayonet chaetae ( Figure 9 F). Thoracic notopodia with 23–35 long-handled acicular uncini in each fascicle ( Figure 9 H–I), teeth decreasing gradually in size away from main fang, dentition covers proximal half of main fang ( Figure 8 E–F). Abdomen with 42 segments (32–42). Anterior segments; two rows of 6–7 elongate, narrowly hooded chaetae, chaetae from upper half as long as chaetae in lower row; 10–15 uncini per torus with main fang surmounted by 3–5 rows of equal size teeth ( Figures 8 G–H, 9J), occupying half the length of main fang, older (dorsal most) uncini smaller than younger uncini (ventral most), main fang not extending beyond breast, breast rectangular with a triangular anterior tip ( Figure 8 H). Posterior segments; one or two very elongate, narrowly hooded chaetae, ca. 50% longer than in anterior segments; 10–12 modified uncini per torus, with several rows (+ 6) of equal size teeth occupying three quarters of the main fang length ( Figures 8 I, 9K). Pygidium with a rounded posterior margin.

Glandular pattern: After staining with methyl green, anterior end of the collar not colored, posterior end dark. Curved belt above ventral shield area not stained ( Figure 8 A–B). Shield of collar densely colored. Body colored uniformly dorsal and ventrally.

Remarks: Dialychone okudai superficially resembles Paradialychone ecaudata by having radiolar tips wide and short, a web extending three quarters of branchial crown length, long pairs of ventral radiolar appendages and a ventral shield horseshoe-shaped. However, a detailed examination of thoracic and abdominal uncini suggests that D. okudai belongs in Dialychone . In addition to D. okudai , 14 accepted species of Dialychone are known ( Tovar-Hernández 2008). Among these D. okudai is unique in having lateral pads on the collar segment, v-shaped notches on dorsal collar margins, paleate chaetae with very long mucros and the anterior peristomial ring lobe digitiform and exposed beyond the collar. For instance, in D. collaris ( Langerhans 1880) , D. normani ( McIntosh 1916) , D. dunerificta (Tovar- Hernández et al 2007), D. longiseta ( Giangrande 1992) , D. quebecensis ( Tovar-Hernández 2007a), D. trilineata ( Tovar-Hernández 2007a) and D. trilobata ( Gallardo 1968) the anterior peristomial ring lobe is bilobed and exposed beyond collar; and triangular with entire tip, not exposed in D. acustica ( Claparède 1870) , D. perkinsi ( Tovar-Hernández 2005) , D. albocincta ( Banse 1972) , D. veleronis ( Banse 1972) , D. arenicola ( Langerhans 1880) , D. australiensis ( Hartman-Schröder 1979) and D. usticensis ( Giangrande et al. 2006) . Dialychone okudai is the first species of this genus known from Japan.

Etymology: The species is named in honor of Professor Shiro Okuda (Hokkaido University) who first studied species of Dialychone (as Chone ) from Hokkaido in recognition of his many years of dedication to the taxonomy of polychaete worms.

Figures

FIGURE 8. Dialychone okudai sp. nov. A – B, dorsal and ventral views of anterior end of methyl green stained holotype. C, paratype NHM-ANEA. 2009.15, thorax and base of crown, showing white glandular belt. D – I, SEM micrographs of chaetae and uncini. D, paleate chaetae from chaetiger 4. E, F, thoracic uncini from chaetiger 3 and 4. G, H, abdominal uncini from anterior chaetiger. I, abdominal uncini from the posterior chaetiger. Scale: 1 mm in A – C.

FIGURE 9. Dialychone okudai sp. nov. A – C, ventral, lateral and dorsal views, respectively, anterior thorax of holotype. D – E, paratype NHM-ANEA. 2009.15. D, radiolar tip. E, inner view of crown. F, thoracic narrowly hooded chaeta. G, paleate chaeta. H – I, thoracic uncini. J, abdominal uncinus from chaetiger 9. K, abdominal uncinus from last chaetiger. Abbreviations: aprl, anterior peristomial ring lobe; dl, dorsal lip; dpa, dorsal pinnular appendage; gg, glandular girdle. Scale: 1 mm in A – E, 25 µm in F – K.