Paradialychone cincta ( Zachs, 1933 ) Zachs, 1933

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 : 3-7

Paradialychone cincta ( Zachs, 1933) new combination

Figures 2–3

Chone cincta Zachs, 1933: 135 .

Material examined. CBM –ZW 1018, Ariake Sound, Kyushu, St. AD20, sandy mud, 20m, 17 September, 2005, by dredge, by K. Mori. CBM-ZW 1019, Ariake Sound, Kyushu, St. AF8D, sandy mud, 27m, by dredge, 12 November, by K. Mori. KMNH-IvR-500.421, Ariake Sound, Kyushu, St. AF7D, 18m, sandy mud, by dredge, 12 November, 2005, dredge, K. Mori. ECOSUR, Ariake Sound, Kyushu, St. AD20D, sandy mud, 20m, 17 September, 2005, by grab-sampler, by K. Mori. SAMA E 3725. Ariake Sound, Kyushu, St. AD19D, shell stones, 35m, by dredge, 17 September, 2005, by K. Mori. ZMUC-POL-2061, Ariake Sound, Kyushu, St. AH13D, sandy mud, 43m, by dredge, 11 November, 2005, K. Mori. KMNH –Iv.R-500.422, Ariake Sound, Kyushu, St. AE20D, sandy bottom, 20m, by dredge, 17 September, 2005, K. Mori. MNHN PNT 10 - Ariake Sound, Kyushu, St. AD20, sandy mud, 20m, 17 September, 2005, by dredge, by K. Mori. NHM-ANEA- 2009.17, Ariake Sound, Kyushu, St. AF7D, sandy mud bottom, 18m, 12 November, 2005, by K. Mori. BPBM- R3394, Ariake Sound, Kyushu, St. AD20, sandy mud, 20m, 17 September, 2005, by dredge, by K. Mori. SMF 18133, Ariake Sound, Kyushu, St. AD20, sandy mud, 20m, 17 September, 2005, by dredge, by K. Mori. USNM 1123952, Ariake Sound, Kyushu, St. AD20, sandy mud, 20m, 17 September, 2005, by dredge, by K. Mori. MBM119725, Ariake Sound, Kyushu, St. AD20, sandy mud, 20m, 17 September, 2005, by dredge, by K. Mori. CMNH-ZW 1689-1692, Ariake Sound, Kyushu, St. AG11D, sandy mud, 26m, 18 September, 2005, by dredge, by K. Mori.

Description. Body cream colored. Body cylindrical. Posterior abdomen compressed dorso-ventrally. Body length 10–12 mm, width 1.0– 1.2 mm. Tubes made of mucus-like material, soft and thin. Insertion of branchial lobes exposed beyond collar in dorsal view ( Figure 3 A). Branchial crown length 4.0–5.0 mm. Radioles: 8–10 pairs. Radiolar tips filiform, slender, long (tip 1.4–1.5 mm versus 4.2 mm crown length). Radiolar skeleton with two rows of cells. Distal pinnules longer than more proximal pinnules. Palmate membrane extends for about one half of branchial crown length. Lateral flanges broad along the outer edges of radioles. Dorsal lips five times longer than wide, without mid-rib ( Figure 3 C). One pair of dorsal pinnular appendages united to each other by palmate membrane, shorter than dorsal lip length. Ventral lips rounded, about one-quarter length of dorsal lips. Ventral radiolar appendages long, about one-half length of crown ( Figure 3 C). Anterior peristomial ring lobe triangular, not extended beyond collar ( Figure 3 B). Ventral margin of collar entire, triangular, higher than dorsal and lateral margins ( Figures 2 A–B, 3A–B). Mid-dorsal collar margin forms a narrow gap ( Figures 2 A, 3A). Dorsal pockets of collar not developed ( Figures 2 A, 3A). Ventral shield of collar circular, poorly discernible, glandular pattern laterally extending towards dorsal side ( Figure 2 A–B). Distal part above ventral shield not stained by methyl green ( Figures 2 A–B, 3A–B). Ratio of posterior peristomial ring collar length versus chaetiger 2 length, in lateral view = 1.5:1. Notopodia of chaetiger 1 with two groups of elongate, narrowly hooded chaetae. Notopodia of chaetigers 2–8 with two irregular rows of elongate, narrowly hooded chaetae ( Figure 3 F), one anterior row with bayonet chaetae, and two posterior rows with symmetrical, paleate chaetae with short mucros ( Figures 2 C, 3D). Neuropodia of chaetigers 2–8 with one row of acicular uncini (ca. 15 in number) with main fang surmounted by 3–4 rows of teeth unequal in size, occupying half the length of main fang ( Figure 2 D–E). Glandular girdle on chaetiger 2 clear, near anterior segment margin dorsally and ventrally; but laterally near posterior segment margin ( Figure 2 A–B). Posterior end of abdomen with a dorsoventral pre-pygidial depression. Abdominal segments: 42–46. Anterior segments with two rows of 6–7 elongate, narrowly hooded chaetae, chaetae from upper half as long as chaetae in posterior row; 10–15 uncini per torus with main fang surmounted by 3–4 rows of unequal size teeth ( Figure 2 F), extending one- half length of main fang, older (dorsal most) uncini smaller than younger uncini (ventral most), breast rectangular ( Figure 3 H). Posterior segments with one or two very elongate, narrowly hooded chaetae, ca. twice longer than in anterior segments; 10–12 uncini per torus, rasp-shaped with 7–8 rows of equal-size teeth, occupying more than three quarters of main fang length ( Figure 2 G). Pygidium with rounded posterior margin.

Glandular pattern: Mid-ventral area of collar deeply stained all around with methyl green, anterior and posterior margins with less stained ( Figures 2 A–B, 3A–B). Ventral shield of collar with dark stain, extending ventrally to second chaetiger. Thoracic chaetiger 2 is stained only in mid-ventrally, lateral margins are not stained or stained only slightly ( Figures 2 A–B, 3A–B). Other thoracic and abdominal segments are stained uniformly dorsally and ventrally.

Remarks: Chone cincta is redescribed here and transferred to Paradialychone . The species has diagnostic features of Paradialychone : 1) thoracic uncini with the main fang surmounted by unequal-size teeth; 2) dorsoventral pre-pygidial depression; 3) anterior abdominal uncini with unequal-size teeth; and 4) posterior abdominal uncini as rasp-shaped plates. Paradialychone contains twelve species ( Tovar-Hernández 2008); among which P. c i n c t a is unique in having thoracic paleate chaetae with short mucros and a horizontally stained, belt-like pattern of the collar. Most species in Paradialychone have a medium-size or long mucro while only two have a minute or indiscernible mucro: P. eiffelturris ( Tovar-Hernández 2007a) and P. paramollis ( Tovar-Hernández 2007a). Paradialychone cincta has a circular ventral collar shield, that is only slightly discernible; in P. eiffelturris ( Tovar-Hernández 2007a) it is Eiffel Tower-shaped and horseshoe-shaped in P. paramollis . Among the species described in this study from Japan, P. c i n c t a is distinct in having paleate chaetae with short mucros (minute in P. katsuuraensis n. sp.; see Tovar-Hernández et al., 2007, and long in P. edomae n. sp.).

The population of P. c i n c t a from Tomioka (Ariake Sound) seems to have an indeterminate growth, as shown in Yun and Kikuchi (1991) and Yun and Nojima (1998). Future studies on members of Dialychone , Paradialychone and Euchone need to take into account the number of chaetigers forming the pre-pygidial depression, since the number of segments, fixed or indeterminate, might be a useful character to distinguish species.

Figures

FIGURE 2. Paradialychone cincta. A, methyl green staining pattern, dorsal view of thorax and base of crown. B, methyl green staining pattern, ventral view of thorax and crown. C, paleate chaeta. D, E, thoracic uncini. F, abdominal uncini from anterior chaetiger. G, abdominal uncini from posterior chaetiger.

FIGURE 3. Paradialychone cincta. A, dorsal view of thorax and anterior abdomen, methyl green staining pattern of collar. B, ventral view of thorax chaetigers, methyl green staining pattern of collar and ventral shields. C, inner margin of crown. D, paleate chaeta. E, thoracic uncinus. F – G, abdominal chaetae. H, abdominal uncinus. Abbreviations: dl, dorsal lip; vl, ventral lip; vra, ventral radiolar appendage. Scale: 1 mm in A – C, 25 µm in D – H.