Longibrachium arariensis, Nishi, Eijiroh & Kato, Tetsuya, 2009

Nishi, Eijiroh & Kato, Tetsuya, 2009, Longibrachium arariensis, a new species of Onuphidae (Annelida: Polychaeta) from the shallow water of Izu Peninsula, central Japan, with notes on its feeding behavior, Zootaxa 2081, pp. 46-56 : 47-49

Longibrachium arariensis sp. nov.

(Japanese common name: “Yatsude-Isome”)

Diagnosis. Antennae of about equal length, comparatively short, reaching to chaetigers 6 to 8. Anterior four pairs of parapodia prolonged, with three distally recurved long hooks and 6–10 small hooks in each; hooks of both sizes with two rows of immovable spines; chaetal sacs extending to chaetigers 12–23; subacicular hooks from chaetiger 30–35.

Material examined. Holotype: CMNH-ZW01695, Koganezaki beach, 34 50.581'N, 138 45.776'E, Arari, Kamo-mura, western part of Izu Peninsula, Shizuoka Prefecture, central Honshu, Japan ( Fig. 1 ), 15 m depth, sandy bottom, collected by K Nin, with scuba gear and fishing equipments, 12, July, 2004. Largest specimen, dissected, jaws in a separate vial.

Paratypes: NHM-ANEA2009.2, collection site is same to the one of holotype, dissected (with 3 extended parapodia); 21, June, 2004, coll. by K. Nin, T. Takaki and M. Takaki. USNM 1122509, dissected, with 4 extended parapodia, without tube, 12 June, 2004, coll. by K Nin. AM W35290, not dissected, with 4 extended parapodia, with tube, 12 June, 2004, coll. by K Nin.

Comparative material. Longibrachium longipes , paratype –AM W 198974.

Description. All type material incomplete, posterior parts lacking; holotype measuring 160 mm in length, for ca. 200 chaetigers, 8 mm wide excluding chaetae and 15 mm wide including chaetae at widest part at anterior part of body; paratypes NHM-ANEA 2009.2 – 40 mm long for 41 chaetigers, 6.5 mm and 10 mm wide (including and excluding chaetae) at anterior part: paratype AM W35290 – 90mm in length for 120 chaetigers, 8 mm and 16 mm wide (including and excluding chaetae) at anterior part. Single dark brown transverse line in dorsal part of each chaetiger, ceratophores and prolonged parapodia of anterior chaetigers, although color faded in some parts. Median part of styles of antennae and palps dark brown; distal part creamy white ( Fig.2 E). Prostomium short with globular frontal lips ( Fig. 3 A, B). Ceratophores of antennae and palps with 6–7 short proximal rings and single long distal ring. Styles gradually tapering, ending in fine tips; palps reaching to chaetiger 2 in holotype and paratypes, lateral and median antennae about equal in length (6.0 to 7.5 mm in length) reaching to chaetiger 7 in holotype, to 6–8 in paratypes ( Fig. 3 A).Nuchal grooves not recognized. Peristomial cirri large, almost half as thick as antennal styles, 0.5 times as long as peristomium, inserted at anterior margin of peristomium between median and lateral antennae ( Fig. 3 A). Peristomium and chaetiger 1 almost twice as long as following chaetigers ( Fig. 3 A). Comparison of size of each specimens, ratio of antennae in length to body width and jaw width in each worm shown in Table 1 .

Modified parapodia (chaetigers 1–4) greatly prolonged, directed anteroventrally ( Figs. 2 A–D;3A,B); parapodia l longest, becoming progressively shorter in following chaetigers. Modified parapodia of all examined specimens partly retracted ( Figs. 2 B, 3A,B), resulting in curved ( Fig. 3 E) or ringed appearance ( Fig. 3 A, B). Smallest paratype (NHM-ANEA 2009.2) with 3 pairs of modified parapodia (chaetigers 1–3). Modified parapodia ( Figs. 2 C, 3E, F, 5A) with small acicular lobe, three papilliform lobes and digitiform postchaetal lobe. Following parapodia ( Fig. 3 B, G) short; with low prechaetal folds, rounded acicular lobe, and subulate postchaetal lobes. Dorsal cirri digitiform with basal swelling developing into basal process by chaetiger 8 ( Figs. 3 H, I, 5C). Ventral cirri subulate in anterior chaetigers. Branchiae as single filaments from chaetiger 6, bifid filaments from chaetiger 9, 3 filaments from 14 or 15, 4 filaments from 15 or 16, 5 filaments from 20 to 22, reaching a maximum of seven filaments by chaetigers 30 to 35 ( Figs. 3 H, I).

Modified parapodia with two types of hooks. Single long distally recurved hook ( Fig. 3 F, 4A, 5A, B) projecting from each of three papilliform lobes (Fig. 5A). Bundle of shorter, thinner hooks ( Fig. 3 F, 4B, 5A) from lower folds. Both long and short hooks with two longitudinal rows of closely spaced spines, except distal part ( Fig. 4 A, B, 5A, B). Chaetal sacs of hooks of parapodia 1–4 extending in body cavity to about chaetigers 23, 22, 13, 12 respectively.

Chaetiger 5 and following segments with limbate and pectinate chaetae. Upper bundle of 8–12 simple limbate chaetae and 1–3 pectinate chaetae (with ca.12 teeth) ( Fig. 4 E), projecting from dorsal pocket. Pectinate chaetae in posterior segments with ca. 20–24 teeth ( Figs. 4 F, 5D). Limbate chaetae of lower bundle consisting of bilimbate ( Fig. 4 C) and long limbate chaetae ( Fig. 4 D). Single bidentate subacicular hook ( Figs. 4 G, 5E) from chaetiger 30–35, two from chaetiger 32 to 39, replacing lower limbate bundle.

Mandibles ( Fig. 3 D) white, strongly calcified; broad, thick shaft and large cutting plates serrated at distal margin. Maxillae ( Fig. 3 C) 4.0 to 4.5 mm in length (from top of Mx I to posterior end of carrier), 2.2 to 2.7 mm in width at Mx I, moderately sclerotized, darker towards inner plates edges. Central triangle of carrier pale brown, basal outer lobes very pale, hardly screlotized. Maxillary formula (based on two paratypes): Mx I=1+1; Mx II=6–8+7–8; Mx III=6–8+0; Mx IV=5–7+7–9; Mx V=1–2+1; MX VI= toothless plate ( Fig. 3 C).

Tube with white, parchment-like inner lining, and outer covering of foraminiferous sand ( Fig. 2 B). Tube opening ca. 10 mm in diameter in holotype and paratypes.

Figures

FIGURE 1. Map of collection site, Izu Penisula, Arari, Kamo-mura, and Koganezaki beach (● with arrow in right).

FIGURE 2. Underwater photos of Longibrachium arariensis new species (photos taken by Mr K. Nin), except for E. A, four pairs of prolonged parapodia protruding from a tube above the substrate. B, the head and parapodia seen from the mouth of tube. C, close-up view of prolonged parapodia. D, prolonged parapodia set down on the substrate. E, ventral view of captured L. arariensis n. sp.

FIGURE 3. Type specimens of Longibrachium arariensis new species. A, anterior part of holotype dorsal view; B, anterior part of paratype AM W 35290, ventral view; C, maxillae of paratype AM W 35290; D, mandible of paratype AMS; E, contracted parapodium of chaetiger 1; F, extended parapodium showing long and short hooks, viewed in underwater photograph (Fig. 2 C); G to I, parapodia of chaetigers 5 (G), 8 (H), 20 (I). Scale is 1 mm.

FIGURE 4. Chaetae of Longibrachium arariensis new species. A, large spiny hook from extended parapodium; B, short spiny hook from the same; C, bilimbate chaeta; D, limbate chaeta; E, pectinate chaeta from chaetiger 6; F, pectinate chaeta from chaetiger 20; subacicular hook from chaetiger 40.

Tables

TABLE 1. Size of type specimens of Longibrachium arariensis new species and L. longipes Paxton, 1986. Sizes are in mm.

Body width at anterior 6.2–6.5 2–5 chaetigers	7.4–8.2	6.5–6.6	8.0	3
No. of segments>200	>120	>41	>50	>22
Length of middle 7.6 antenna	7.6	7.2	7.5	6
Length of lateral 6.2 antenna	8	7.2	7.0	4.5
Middle antennae 7–8 ctg. reaching to	7–8 ctg.	7–8 ctg.	6 ctg.	10–14 ctg.
Length of jaw - (maxillae)	4	4.5	4.5	2.5
Width of jaw - (maxillae)	2.2	2.7	2.1	1.6
Ratio of middle 1.2 antenna to body width	0.97	1.1	0.94	ca.2.0
Ratio of middle - antenna to jaw width	3.4	2.7	3.6	3.8