Phyllochaetopterus lauensis, Rouse, Eijiroh Nishi Greg W., 2007

Phyllochaetopterus lauensis new species

( Figs. 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 )

Material Examined.— Holotype ( SAMA E 3672), complete, with a tube twice the length of the body and 2 paratypes ( SAMA E 3673, OMNH-Iv 5025) complete, with fragments of tube, 5 paratypes (CBM-ZW- 1006, SAM E 3674, SIO-BIC-A 976 and A 977, USNM 1106928) incomplete, with a fragment of tube, 1 paratype ( USNM 1106929) incomplete, without tube. Holotype and 8 paratypes were collected during dive 145 of the Deep-Sea Research Vehicle (DSV) Jason II at the hydrothermal vent locality known as Hine Hina, Southern Valu Fa Ridge, Lau back-arc basin 22 ° 31.9393S; 176 ° 43.1038W near Tonga on 22 May, 2005, a cluster of chaetopterid tubes was collected by manipulator at 1818 m depth in the vicinity of hydrothermal vents.

Additional material examined:

For comparison the following Phyllochaetopterus specimens from the Pacific area were also studied:

Phyllochaetopterus cf. verrilli Treadwell, 1943 : CMNH-ZW-(uncatalogued), Sesoko Island, Okinawa Island, sandy mud flat, 1–2 m deep, February 1987, by E. Nishi.

Phyllochaetopterus claparedii McIntosh, 1885 : CMNH-ZW-(uncatalogued), Tateyama, Boso Peninsula, 5 to 6m m deep, sandy bottom, by E. Nishi, 15 October 1998.

Phyllochaetopterus . sp.: CMNH-ZW (uncatalogued), Port Jackson, Bottle and Glass Rocks, Sydney Harbour, Australia, 33 ° 58 S, 151 0 0 E, 4 m. depth, 4 April 1999 by G. W. Rouse.

Diagnosis.— Phyllochaetopterus of small size, eyes absent; A 1 dorsally with short ‘cirri’ with slightly protruding internal chaetae; A 4 with 1–2 stout brown cutting chaetae, pear-shaped in frontal view, head of chaeta slightly inflated, with row of small teeth on both lateral edges. Region B with two chaetigers; B notopodia foliaceous, bilobed; B neuropodia each with single band of uncini; C notopodia digitiform, with single protruding chaeta; C neuropodia bilobed, with two bands of uncini anteriorly, with single band posteriorly.

Body formula of species: 9–10 A+ 2 B+ at least ca. 40 C = ca. 52 or more chaetigers; Region A 5 –A 9 of plastron (glandular ventral shield) with distinctive light brown (A 5), whitish (A 6 –A 7), and light brown (A 8 and A 9) transverse bands observed in alcohol-preserved specimens. Tube transparent or translucent, partly amber to white in color, weakly annulated, without septa or partitions.

Description (based on holotype). — Holotype complete (some paratypes lacking posterior part of region C), 26 mm long excluding palps; palps, paired 6mm long (about 5 to 8 mm long in paratypes), grooved, arising from near posterolateral border of prostomium ( Fig. 3 View FIGURE 3 A). Body 1.0–1.4 mm wide at ventral shield. Body creamy white except for ventral shield in alcohol preserved specimens. Region A narrow, 1.0-1.2mm width, 5.0 mm long for 9 chaetigers (10 chaetigers in some paratypes and 4.0 to 5.0 mm length). Prostomium a distinct lobe, peristomium broad and plate-like, appearing slightly cleft when viewed from ventral side ( Fig. 3 View FIGURE 3 A, B, C). Eyespots absent. Cirri of 1 st chaetiger small and short ( Fig. 3 View FIGURE 3 A, E), with slightly protruding internal chaetae. Dorsal groove ciliated, extending from base of palps along body regions A, B and C ( Fig. 3 View FIGURE 3 E). Ventrum of region A with a long slender plastron (ventral glandular shields), separated into 4 sections based on color ( Fig. 3 View FIGURE 3 A, B, C), color of each section varying among type specimens. In holotype, Section I, longer than others, from peristomium to chaetiger A 4 or anterior A 5, white in holotype ( Fig. 3 View FIGURE 3 B). In some paratypes ( Fig. 3 View FIGURE 3 A and C), pale, very light brown. Section II, chaetiger A 5 only or A 5 to A 6 ( Figs. 3 View FIGURE 3 A,C), dark brown in holotype, light or dark brown in paratypes. Section III comprises chaetigers A 6 to A 7 or A 7 only, pale white in holotype and paratypes ( Fig. 3 View FIGURE 3 A, B, C). Section IV comprises A 8 and A 9 (plus A 10 in some paratypes) (A 8- 10 in Fig. 3 View FIGURE 3 A; A 7–9 in Fig. 3 View FIGURE 3 B; A 9 in Fig. 3 View FIGURE 3 C), light brown anteriorly and progressively lighter in color in posteriorly in holotype and some paratypes ( Fig. 3 View FIGURE 3 A, B), no color in others ( Fig. 3 View FIGURE 3 C). In holotype and paratype ( SAMA E 3673) Section II darker than anterior Section IV.

Chaetigers A 1 to A 3 short, parapodia with a single row of 10 to 20 lanceolate chaetae; A 4 elongate, with one large (cutting) chaeta in each notopodium (one undeveloped chaeta in paratypes CBM-ZW 1006), and more than 10 lanceolate chaetae; A 5 to A 9 (or A 10 in some paratypes) slightly longer and wider than anterior three chaetigers, with single row of 20 to 30 lanceolate chaetae. Cutting chaetae of A 4 with obliquely ellipsoidal distal end; head slightly inflated, slightly wider than shaft, pear-shaped in frontal view, tip slightly pointed ( Fig. 4 View FIGURE 4 F, G, H); shaft nearly semi-circular in horizontal section, lateral or ventral grooves absent. Total length of cutting chaetae 300-400 m; head ca. 80 m in width, 90 m in length ( Figs. 2 View FIGURE 2 A, B, C, 4 F, G, H). Middle region (region B) comprises 2 chaetigers only, each slightly longer than anterior chaetigers; notopodia bilobed, dorsal lobe branched into a Y-shape (= dichotomously branched) ( Fig. 3 View FIGURE 3 A, B, C, D). Paddle and cupule absent. B 1 and B 2 nearly same length. Beneath last A chaetiger and first B notopodia, a pair of liquidfilled swellings present ( Fig. 3 View FIGURE 3 D). B-region neuropodia unilobed with one row of minute uncini: uncini nearly triangular, with ca. 25 teeth ( Fig. 4 View FIGURE 4 J). Posterior region (region C) with 25 chaetigers in holotype (up to 40 chaetigers in three paratypes, though incomplete). Anterior C-region chaetigers elongate, extended and longer than regions A and B chaetigers ( Figs. 3 View FIGURE 3 A, 4 A). Notopodia unilobed, knob-like tip each with a single chaeta ( Fig. 4 View FIGURE 4 A, B, C). Neuropodia bilobed in anterior 10 to 12 chaetigers ( Fig. 4 View FIGURE 4 A, B) and unilobed in posterior chaetigers ( Fig. 4 View FIGURE 4 C). Uncini similar to those of region-B, but smaller. Tube fragile, 1.5 to 2.0 mm in diameter, slender, nearly straight, weakly annulated and pleated in parts. Tube wall thin, transparent, partly light amber to light brown. Septa or partitions absent.

Etymology.—The species epithet lauensis is derived from the name of the type locality, the Lau back-arc basin.

Remarks. —Among the Phyllochaetopterus , P. lauensis n. sp. is easily distinguishable from other members of the genus by its alternating white/brown patterning on the plastron. Similar patterning is found in Spiochaetopterus spp. (e.g., Bhaud, 1998; Nishi et al., 2004), and the feature is used for distinguishing among the species of this genus. In Phyllochaetopterus , however, the ventral shield (glandular area) is usually a single color or separated into only two colored portions, anterior and posterior. For Phyllochaetopterus in general, the A 4 chaetal numbers and color, the number of region-B chaetigers and tube characters are used for distinguishing species. Based on those characters, we provide here a summary table ( Table 1 View TABLE 1 ).

*H.-S. = Hartmann-Schröder Among the 19 previously described species of Phyllochaetopterus , twelve species have 1–2 cutting chaetae on notopodia of A 4, while others have a row of 3–8 cutting chaetae ( Table 1 View TABLE 1 , Bhaud 1977, Kudenov 1975). These taxa can also be distinguished further by the number of region-B chaetigers and separated into four groups ( Table 1 View TABLE 1 ):

A—having 1–2 cutting chaetae in A 4 notopodia, with two region-B chaetigers;

B—having 1–2 cutting chaetae in A 4, with three or more region-B chaetigers;

C—having a row of more than 6 cutting chaetae in A 4, with two region-B chaetigers; D—having more than 6 cutting chaetae in A 4, with three or more region-B chaetigers.

Phyllochaetopterus lauensis n. sp. belongs in group A, which now contains 4 described species; P. gracilis Grube, 1863 , P. claparedii McIntosh, 1885 , P. limicolus Hartman, 1960 and P. monroi Hartman, 1967 . Apart from all other Phyllochaetopterus lacking the marked patterning described here for P. lauensis n. sp., Phyllochaetopterus gracilis has 10–11 region-A chaetigers whereas P. lauensis n. sp. has only 9–10. Phyllochaetopterus limicolus lacks the inflated head in A 4 modified chaetae ( Bhaud 1977) seen in P. lauensis n. sp. ( Fig. 2 View FIGURE 2 B, C). Phyllochaetopterus claparedii is morphologically most similar to P. lauensis n. sp., but the former has long, clavate cirri on A 1 and region-B chaetigers are elongate and longer than those of region A ( McIntosh 1885). Phyllochaetopterus lauensis n. sp. on the other hand has short cirri on A 1, and region-B chaetigers are not especially elongate ( Fig. 3 View FIGURE 3 A, E). Additionally, P. lauensis n. sp. is also distinguishable from P. claparedii by the number of chaetae in the C notopodia; P. claparedii and P. aciculigerus have 3–4 chaetae in posterior C notopodia and all other species of the genus have only a single chaeta. P. monroi Hartman has minute papillae at the base of C notopodia, whereas P. lauensis n. sp has no such papillae. We also compared the new species to specimens of P. claparedii collected at Tateyama, Boso Peninsula, Chiba Prefecture, particularly with regards to the A 4 chaetal structure using scanning electron microscopy. Phyllochaetopterus lauensis n. sp. and P. claparedii both have 9–10 A+ 2 B, and 1–2 A 4 cutting chaetae with a slightly inflated head with a slanting edge in lateral view ( Fig. 2 View FIGURE 2 A, F). However, in frontal view the A 4 cutting chaetae of P. lauensis are pear-shaped ( Fig. 2 View FIGURE 2 A–C) and those of P. claparedii are asymmetrically cordate - a skewed heart shape ( Fig. 2 View FIGURE 2 E, F).