Paradialychone katsuuraensis Nishi, Tanaka, Tovar-Hernández & Giangrande, 2009, new species

Paradialychone katsuuraensis new species

Japanese name: Moba-Keyarimushi Figures 6–7

Material examined. Type material. HOLOTYPE — CBM –ZW–557, Yoshio, Katsuura, Boso Peninsula, subtidal sandy mud bottom, 1–5 m, among Thalassia marina thalli, 15 October, 1998, coll. E. Nishi by hand. PARATYPES —CBM-ZW-552, Yoshio, Katsuura, Boso Peninsula, subtidal sandy mud bottom, 1–5 m, among Thalassia marina thalli, 15 October, 1998, coll. E. Nishi by hand. CBM-ZW 554, Yoshio, Katsuura, Boso Peninsula, subtidal sandy mud bottom, 1–5 m, among Thalassia marina thalli, 15 October, 1998, coll. E. Nishi by hand. CBM-ZW-555, Yoshio, Katsuura, Boso Peninsula, subtidal sandy mud bottom, 1–5 m, among Thalassia marina thalli, 15 October, 1998, coll. E. Nishi by hand. CBM-ZW-561, Yoshio, Katsuura, Boso Peninsula, subtidal sandy mud bottom, 1–5 m, among Thalassia marina thalli, 15 October, 1998, Coll. E. Nishi by hand. ECOSUR 0 0 91, same collection data as holotype.

Description. Body brown, glandular girdle white and branchial crown pale in live specimens (Figure 6 A–B photo of live worms). Body cylindrical, posterior abdomen inflated in some specimens (Figure 6 B). Adult holotype 40 mm long excluding radioles, 50–80 mm in paratypes, width 0.5 mm in posterior thorax in holotype, 1.6 to 2.0 mm in paratypes. Branchial crown length 6.0 mm in holotype, 7.0 mm in largest paratypes. Insertion of branchial lobes not exposed beyond collar (Figures 6 C–D, 7B–C). Base of branchial crown shorter than collar segment. Branchial crown length 6.0 mm in holotype, 5.0–7.0 mm in paratypes. Ten pairs of radioles in holotype, 10–12 in paratypes, connected for almost entire length by palmate membrane (Figure 7 D–E). Radioles with longest pinnules three quarters of their length. Radiolar tips filiform (Figure 7 E–F). Lateral flanges narrow along the outer edges of radioles. Dorsal lips with radiolar appendages (Figure 7 G). A variable number of dorsal pinnular appendages, from 1 to six, 1 in holotype (Figure 7 G), with different lengths. Paired ventral lips same lengths as dorsal lips, pointed (Figure 7 G). Ventral radiolar appendages absent. Ventral peristomial lobe projection triangular with entire tip (Figure 7 C), not exposed beyond collar or slightly exposed beyond collar. Collar margin entire, ventral margin slightly higher than lateral and dorsal (Figure 7 B–C), reaching approximately to base of branchiae. Dorsal gap narrow. Dorsal pockets present. Collar slightly higher ventrally than dorsally in lateral view. Peristomial ring collar 1.5 times longer than chaetiger 2 in lateral view. Ventral shield of collar undifferentiated (pentagonal-shaped using methyl green, Figure 6 C). Chaetiger 2 glandular girdle present, slightly wider dorsally than ventrally (Figures 6 C–D, 7A–C, I–J). Ventral shields not discernible (Figures 6 C, 7A). First thoracic chaetiger with single row of long, narrowly hooded chaetae. Following thoracic segments with three kinds of notochaetae: superior group of long narrowly hooded chaetae, inferior group with short limbate chaetae and paleate chaetae with a minute mucros or completely rounded (Figures 6 E–F, 7N) and slender pointed bayonet chaetae (Figure 7 K–L). Thoracic notopodia with 23 – 35 long-handled acicular uncini in each fascicle, with five rows of unequal in size teeth in lateral and frontal views (Figures 6 G, 7M), covering proximal half of main fang. Abdomen with 40 chaetigers in holotype, 40–45 in paratypes. Anterior abdominal notopodial tori with 14–40 uncini, each with quadrate base (Figure 7 P–Q), and first tooth over main fang larger than following three rows of teeth (Figures 6 H, 7P). Shape of uncini nearly constant within each torus, but main fang progressively smaller in posterior chaetigers. In posterior abdomen, uncini rasp-shaped (Figures 6 I, 7Q); teeth equal size, covering three quarters of main fang length. Abdominal neuropodia with 13–14 narrowly hooded chaetae in two rows per fascicle. Posterior abdominal margin triangular, slightly longer than wide, without cirrus.

Adult holotype (female). Sexes separate with gametes occurring laterally between dorsal and ventral longitudinal muscle bundles in posterior thoracic and abdominal chaetigers. Eggs with asynchronous development, up to 0.1 mm in diameter.

Glandular pattern: Methyl green stain dorsally and ventrally (Figure 6 C–D) on most of the body including pygidium. Staining is absent in radioles, anterior margin of collar, glandular girdle on chaetiger 2, intersegmental furrow, fecal groove, around parapodia, and narrow band of cells encircling each segment at level of chaetae.

Distribution: Paradialychone katsuuraensis is commonly found in shallow waters in Thalassia seagrass beds at Yoshio, Katsuura, Boso Peninsula (Figure 6 A). The species occurs in sandy to muddy substrates in depths of 0.5 to 5 m, in abundance occasionally exceeding 50 individuals/m2.

Remarks: In Paradialychone only three species have a glandular girdle on chaetiger 2 whose width is not homogeneous: in P. gambiae and P. paracincta (Hartmann-Schröder 1962) the girdle is wider laterally while in P. katsuuraensis wider dorsally. Also, P. g a m b i a e has a girdle on chaetiger 9 (absent in P. katsuuraensis n. sp. and P. paracincta). Paradialychone katsuuraensis, P. eiffelturris and P. paramollis have paleate chaetae with minute mucros. In P. katsuuraensis, the girdle on chaetiger 2 is broad dorsally, and the ventral shield of collar is undifferentiated and pentagonal-shaped when is stained with methyl green (horseshoe-shaped in P. paramollis and Eiffel Tower-shaped in P. eiffelturris). Paradialychone katsuuraensis is distributed in Japan while P. paramollis and P. eiffelturris are species with wide distribution in the Pacific coast of the United States.

The new species is similar to Paradialychone ecaudata (= C. teres sensu Okuda 1934, 1946; Imajima and Hartman 1964); but the two are distinguished by following characters. In P. katsuuraensis the anterior peristomial ring lobe is triangular, not exposed beyond collar segment (Figures 7 B–C), and in P. ecaudata it is digitiform, and distinctly exposed beyond collar (Banse 1972: 475, Fig. 6 e; Tovar-Hernández 2007a:526, Fig 4 G). Paleate chaetae have long pointed tips in P. ecaudata but in P. katsuuraensis only minute tips or none at all (Figures 8 N, 9E–F). Paradialyhone katsuuraensis and C. ecaudata are primarily differentiated in the presence of a glandular girdle on chaetiger 2 broad dorsally; the latter with a uniformly narrow ring.

Paradialychone katsuuraensis is unique among congeners distributed in Japan by having a pentagonalshaped ventral shield on the collar, glandular girdle on chaetiger 2 broad dorsally, and paleate chaetae with minute mucros. For comparison, P. c i n c t a and P. katsuuraensis have a horseshoe-shaped ventral collar shield; P. c i n c t a have paleate chaetae with short mucros and P. edomae long mucros; P. c i n c t a and P. edomae have a narrow glandular girdle on chaetiger 2.

Paradialychone katsuuraensis shares the same distribution with other species belonging to the related genera in Japan: Chone duneri, P. filicaudata (Southern, 1914), C. teres (Okuda 1934: 236, 1946: 171; Imajima and Hartman 1964: 365; Imajima 1961, 1963, see Banse 1972) and P. cincta

Etymology: The specific epithet is named after type locality, Katsuura City, Boso Peninsula. The Japanese name Moba means seagrass bed, which the new specie commonly occurred (Figure 6 A), while· keyarimushi means sabellid polychaetes.