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

Rouse, Eijiroh Nishi Greg W., 2007, A new species of Phyllochaetopterus (Chaetopteridae: Annelida) from near hydrothermal vents in the Lau Basin, western Pacific Ocean, Zootaxa 1621, pp. 55-64 : 56-62

Phyllochaetopterus lauensis new species

( Figs. 1–4 )

Material Examined.— Holotype ( SAMA E3672), complete, with a tube twice the length of the body and 2 paratypes ( SAMA E3673, OMNH-Iv5025) complete, with fragments of tube, 5 paratypes (CBM-ZW-1006, SAM E3674, SIO-BIC-A976 and A977, 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; A1 dorsally with short ‘cirri’ with slightly protruding internal chaetae; A4 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: 9–10A+2B+ at least ca. 40C = ca. 52 or more chaetigers; Region A5–A9 of plastron (glandular ventral shield) with distinctive light brown (A5), whitish (A6–A7), and light brown (A8 and A9) 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 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 A, B, C). Eyespots absent. Cirri of 1st chaetiger small and short ( Fig. 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 E). Ventrum of region A with a long slender plastron (ventral glandular shields), separated into 4 sections based on color ( Fig. 3 A, B, C), color of each section varying among type specimens. In holotype, Section I, longer than others, from peristomium to chaetiger A4 or anterior A5, white in holotype ( Fig. 3 B). In some paratypes ( Fig. 3 A and C), pale, very light brown. Section II, chaetiger A5 only or A5 to A6 ( Figs. 3 A,C), dark brown in holotype, light or dark brown in paratypes. Section III comprises chaetigers A6 to A7 or A7 only, pale white in holotype and paratypes ( Fig. 3 A, B, C). Section IV comprises A8 and A 9 (plus A 10 in some paratypes) (A 8- 10 in Fig. 3 A; A 7–9 in Fig. 3 B; A 9 in Fig. 3 C), light brown anteriorly and progressively lighter in color in posteriorly in holotype and some paratypes ( Fig. 3 A, B), no color in others ( Fig. 3 C). In holotype and paratype (SAMA E3673) Section II darker than anterior Section IV.

Chaetigers A1 to A3 short, parapodia with a single row of 10 to 20 lanceolate chaetae; A4 elongate, with one large (cutting) chaeta in each notopodium (one undeveloped chaeta in paratypes CBM-ZW 1006), and more than 10 lanceolate chaetae; A5 to A9 (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 A4 with obliquely ellipsoidal distal end; head slightly inflated, slightly wider than shaft, pear-shaped in frontal view, tip slightly pointed ( Fig. 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 A, B, C, 4F, 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 A, B, C, D). Paddle and cupule absent. B1 and B2 nearly same length. Beneath last A chaetiger and first B notopodia, a pair of liquidfilled swellings present ( Fig. 3 D). B-region neuropodia unilobed with one row of minute uncini: uncini nearly triangular, with ca. 25 teeth ( Fig. 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 A, 4A). Notopodia unilobed, knob-like tip each with a single chaeta ( Fig. 4 A, B, C). Neuropodia bilobed in anterior 10 to 12 chaetigers ( Fig. 4 A, B) and unilobed in posterior chaetigers ( Fig. 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 A4 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 ).

*H.-S. = Hartmann-Schröder Among the 19 previously described species of Phyllochaetopterus , twelve species have 1–2 cutting chaetae on notopodia of A4, while others have a row of 3–8 cutting chaetae ( 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 ):

A—having 1–2 cutting chaetae in A4 notopodia, with two region-B chaetigers;

B—having 1–2 cutting chaetae in A4, with three or more region-B chaetigers;

C—having a row of more than 6 cutting chaetae in A4, with two region-B chaetigers; D—having more than 6 cutting chaetae in A4, 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 A4 modified chaetae ( Bhaud 1977) seen in P. lauensis n. sp. ( Fig. 2 B, C). Phyllochaetopterus claparedii is morphologically most similar to P. lauensis n. sp., but the former has long, clavate cirri on A1 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 A1, and region-B chaetigers are not especially elongate ( Fig. 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 A4 chaetal structure using scanning electron microscopy. Phyllochaetopterus lauensis n. sp. and P. claparedii both have 9–10A+2B, and 1–2 A4 cutting chaetae with a slightly inflated head with a slanting edge in lateral view ( Fig. 2 A, F). However, in frontal view the A4 cutting chaetae of P. lauensis are pear-shaped ( Fig. 2 A–C) and those of P. claparedii are asymmetrically cordate - a skewed heart shape ( Fig. 2 E, F).

Figures

FIGURE 1. Phyllochaetopterus lauensis n. sp. Photographs of live worms. A. Tube with live animal inside. B – E. Paratype-SAMA-E- 3673. B. Right dorsolateral view. C. Dorsal view, showing three body regions; regions A and B pale, region C dark green; A 4 cutting chaetae light brown to amber; palps (p) white; note that region A has 9 left and 10 right notopodia. D. Lateral view showing stout cutting chaeta (cc) of A 4 and notopodia (n) of B 1 and B 2. Arrow points to pigmented section of plastron. E. Dorsal view of anterior end showing cirri (c), dorsal groove (dg) and cutting chaetae.

FIGURE 2. Phyllochaetopterus lauensis n. sp. and SEM micrographs of A 4 modified chaetae (A – C). A, B, lateral view. C, frontal view of head. D, uncini of B 2. P. claparedii McIntosh, 1885 from Tateyama, Boso Peninsula, Tokyo Bay, CMNH-ZW (uncatalogued). E, F, A 4 modified chaetae. E, ventral view. F, frontal view of head.

FIGURE 3. Phyllochaetopterus lauensis n. sp., A, Lateral view of paratype OMNH-Iv 5025. Arrows point to cirri of chaetiger 1. Four sections of plastron indicated by numbers 1 - IV. B, Lateral view of head and A and B regions of the holotype. Four sections of plastron indicated by numbers I-IV. C, Ventral view of paratype USNM 1106928, showing different pigmentation pattern of plastron. D, Paratype OMNH-Iv 5025, close-up dorsal view of A 9 to C 1 showing Bregion parapodia and fluid-filled swellings (sw). E, Paratype SAMA E 3673, close-up dorsal view of head to chaetiger A 1, showing small cirri of first chaetiger (arrows) with projecting internal chaetae.

FIGURE 4. Phyllochaetopterus lauensis n. sp., holotype and paratypes SIO-BIC-A 976 and SAMA E 3673. A – C, lateral and ventral views of region C; smaller, more posterior segments in Fig. 1 A might be regenerated; see also Fig. 1 B, segments 5 C (larger) and 6 C and following (smaller). D, Part of pygidium and posterior chaetigers, ventral view. E, Tube of paratype (SAMA-E 3673). F to J drawn from SEM micrographs. F – H, modified chaetae of A 4. F, lateral view of anterior part. G and H, frontal view of head. I, lanceolate leaf-like chaeta of region A. J, uncinus of B 2.

Tables

TABLE 1. Comparisons of Phyllochaetopterus species. Character states taken from Crossland (1903, 1904), Caullery (1944), Day (1967), Gibbs (1971), Bhaud (1977), Nishi & Arai (1997). Unless otherwise indicated, information is from the original descriptions.

	Species	Type locality	No.pairs of A4 chaetae	No. region-B chaetigers	No. region A chaetigers	Type	Remarks
1	lauensis n. sp.	Lau Basin, off Tonga	1–2	2	9–10	A	This study
2	claparedii McIntosh, 1885	Japan	1–2	2	9–10	A	C notopodia with row of chaetae
3	limicolus Hartman, 1960	San Pedro Basin (Calif.)	1–2	2	9	A	See also Blake (1996)
4	gracilis Grube, 1863	Crivizza, Adriatic Sea	1–3	2	10–11	A	A4 with 3 chaetae (Crossland 1903)
5	monroi Hartman, 1967	Straits of Magellan	1	2	9	A
6	prolifica Potts, 1914	NW Pacific	1	4–12	9–12	B	Up to 60 mm long, 0.8 mm wide
7	ramosus Willey, 1905	Sri Lanka	1–2	16	15	B	25 mm long, 1.5 mm wide
8	anglica Potts, 1914	British waters	1–2	11–25	13–16	B
9	gardineri Crossland, 1904	Maldives	1–2	15	15	B	A4 with 3 chaetae (Crossland 1904)
10	socialis Claparède, 1868	Medit. & Atlantic	1–2	9(7–24)	13 (10–18)	B	20–30 mm long?
11	pictus Crossland, 1903	Kenya	1–2	3–9	12–16	B	C notopodia with 1 chaeta
12	verrilli Treadwell, 1943	Hawai'i	3 (+3)(in a row)	2	9	C	11–14 mm long, 0.6–1.0 mm wide
13	brevitentaculata H–S, 1965 *	Palmyra	6 (in a row)	2	9	C	9 mm long and 1mm wide
14	herdmani Willey, 1905	Sri Lanka	8-9(in a row)	2	9–10	C	80 mm long, A1 cirri with1internal chaetae
15	aciculigerus Crossland, 1904	Maldives	8 (in a row)	2	9	C
16	elioti Crossland, 1903	Tanzania (Zanzibar)	2–3(in a row)	20–25	13–17	D	50–100 mm long, 2–3 mm wide
17	fallax Claparède, 1868	Italy	1?	13	19	D?	ca. 3 cm long
18	sibogae Caullery, 1944	Kabia Is., Indonesia	1–3	at least 5	13–14	?
19	arabicus Grube, 1869	Red Sea	2–4	2	9	?	35 chaetigers Grube considers species close to P. gracilis (p. 28)
20	major Claparède, 1868	Italy	1	2	10	A?	25–30 cm long, 4–5 mm wide