Eunice dilatata Grube, 1877

Hsueh, Pan-Wen & Li, Yan-Huei, 2014, New species and new records of eunicids (Polychaeta, Eunicidae) from Taiwan, Zootaxa 3802 (2), pp. 151-172 : 155-158

Eunice dilatata Grube, 1877

Fig. 3

Eunice dilatata Grube 1877: 530, 1878: 100 ;— Fauchald 1986: 248, figs 29–34, 1992: 121–123, fig. 38a–i, tables 30, 38;— Imajima 2007: 328 –329, fig. 96a–p.

Material examined. Taiwan: Two specimens ( NMNS 2572-122, NMNS 6992-1), Dawen (21°57´22˝N, 120°45´17˝E), Pingtung County, subtidal hard-bottom, 4–6 m deep, August 14, 1996; one specimen ( NMNS 2572- 120), Houdaizi (23°21´52˝N, 119°33´11˝E), Penghu County, intertidal hard-bottom, June 15, 1994; one specimen ( NMNS 2572-115-1), Kenting (21°56´29˝N, 120°47´53˝E), Pingtung County, intertidal hard-bottom, August 22, 1995; seven specimens ( NMNS 6992-2~3, NMNS 6992-9~11, NMNS 6992-13~15), Jihuei (23°06´52˝N, 121°24´11˝E), Taitung County, intertidal algal and coral mixed reefs, October 14, 2007, December 5, 2009, August 8, 23, 27, 2010 and October 9, 2010, respectively; five specimens ( NMNS 6992-4~5, NMNS 6992-6~8), Wanlitong (21°59´45˝N, 120°42´12˝E), Pingtung County, intertidal coral reefs, December 14–15, 2010 and March 15, 2008, respectively; one specimen ( NMNS 6992-12), Shitiping (23°28´58˝N, 121°30´46˝E), Hualien County, rocky intertidal, August 27, 2010.

Description. Complete specimen (NMNS6992-12), sex unknown, total body length 237 mm, with 304 chaetigers; maximum width at chaetiger 26, about 5.0 mm; length through chaetiger 10, about 17.6 mm; chaetiger 10 width, about 4.5 mm. Three anal cirri present, elongate and tapering, without articulations; superior anal cirrus longer and broader at base than inferior cirri ( Fig. 3 D).

Prostomium distinctly shorter than peristomium, about equal width and less than 1/2 as deep as peristomium, prostomial lobes anteriorly rounded, dorsally flattenned, separated by deep median groove ( Fig. 3 A, C). Eyes present, situated posteriorly to base of palps, rounded and black. Prostomial palps and antennae arranged in semicircular, median antenna isolated by gap, similar in thickness; palpophores and ceratophores bases ring-shaped, without articulations; palpostyles and ceratostyles digitiform, distally tapering, with inconspicuous articulations; A-II 12 articulations, A-I 9 articulations, A-III 10 articulations, both palps 4 articulations; A-II to chaetiger 1, AI and A-III to posterior peristomium, palps reaching middle of anterior peristomium. Peristomial cirri tapering and reaching middle anterior peristomium, without articulations ( Fig. 3 A–C).

Maxillary formula: 1+1, 4+4, 5+0, 4+5, 1+1; MxII teeth more robust than teeth on MxIII and MxIV ( Fig. 3 E); mandibles flat ( Fig. 3 F).

Branchiae present, pectinate, distinctly longer than dorsal cirri ( Fig. 3 H), first present on chaetiger 16 to chaetiger 288, terminating before posterior body, over 65% of all chaetigers branchiate; branchial filament single modal distribution, chaetiger 16 and last 19 chaetigers with single filament ( Fig. 3 G), reaching maximum of 7 filaments between chaetiger 27 and chaetiger 42, followed by 6 filaments at chaetiger 25 and chaetiger 43 to 52, filament number declines after chaetiger 52. Branchial filaments longer than dorsal cirri, tapering ( Fig. 3 H).

Anterior neuropodial acicular lobes distally rounded, acicular lobes truncated at middle segments and triangle at posterior segments; aciculae emerging above midline; prechaetal lobes truncate, postchaetal lobes rounded. First 6 to 7 ventral cirri bases without inflation, digitiform; median base ovate inflated; posterior base, digitiform, without inflation. First 10 dorsal cirri digitiform, narrow at base, elongate and tapering thereafter, without articulations ( Fig. 3 G–H).

Limbate chaetae elongate, longest of all chaetae, marginally smooth, internal striations present ( Fig. 3 I). Pectinate chaetae furled, flaring, marginal teeth heterodont, 16–20 inner teeth ( Fig. 3 J). Chaetigers before the presence of branchiae with about 20 compound falcigers, reducing to 5 compound falcigers on posterior segments; shafts of compound falcigers distal slightly inflated, tapering, beak-like, marginally serrated, internal striations present; appendages broad and robust, tapering, bidentate; proximal tooth sharp triangle, almost perpendicular to axis of appendage, smaller than distal tooth at anterior segments, about equal to distal tooth at posterior segments, distal tooth scimitar-shaped, both proximal and distal tooth directed laterally ( Fig. 3 K); guards marginally serrated, without mucros; pseudo-compound falcigers and compound spinigers absent. Aciculae straight, distally tapering, cross-sections rounded; first 19 chaetigers with paired aciculae, light brown, single acicula thereafter, brown; separation between core and sheath distinct in both aciculae and subacicular hooks. Subacicular hooks brown, bidentate, present from chaetiger 25 to last chaetiger, single per chaetiger; shafts of hooks straight, distally tapering; proximal and distal tooth about equal, distally blunt, directed anterolaterally, separated by small gap ( Fig. 3 L–M).

Remarks. This eunicid species is easily identified by its unique flattenned body shape and possession of a large bundle of falcigers on the anterior chaetigers, which is often seen in the genus Marphysa Quatrefages, 1865 ( Grube 1877: 530; Fauchald 1986: 248, 1992: 121; Imajima 2007: 329). Other morphological characters of this species, such as absence of articulation on palps and antennae of the prostomium, shape of compound falcigers, limbate and pectinate chaetae, colouration and shape of aciculae and subacicular hooks, mostly agree with Fauchald (1986: 248, Figs. 29–34, 1992: 121, Fig. 38a–i) and Imajima (2007: 328–329, Fig. 96a–p), with exception of the number of anal cirri ( Fig. 3 ). Imajima (2007: 328–9, Fig. 96i) reported two anal cirri, but our specimens have 3 anal cirri ( Fig. 3 D).

As in many congeners, morphological characters such as the chaetiger on which the branchiae first appeared, maximum number of branchial filament, chaetiger number on which the first subacicular hooks occurs, etc., in E. dilatata are considered variable features ( Miura 1986; Fauchald 1986, 1992; Lu & Fauchald 1998). Our material of E. dilatata , also exhibits no significant positive correlation of the above-mentioned parameters with body size ( Fig. 4 ).

This species was previously only recorded from south of the equator Ocean (Timor, Indonesia, around 10° S) ( Grube 1877; Fauchald 1986, 1992). The Northern Hemisphere distribution was only recently reported, ranging from Nii-jima, Izu Islands (about 34°26´N) to Iriomote, Okinawa Islands (24°18´N) ( Imajima 2007). This species was collected from sites scattered on rocky coasts in Taiwan and Penghu islands, ranging from 23°28´N to 21°57´N (Fig. 1), which may be considered as a southward extension of the southern Japan distribution. Additional collecting from Southeast Asian waters, including Philippines, Borneo and Sulawesi, Indonesia may or may not confirm this disjunct distribution.

Figures

FIGURE 3. Eunice dilatata Grube, 1877 collected in the present study. A, whole body, showing the characteristic of the species –– the compressed body at maximum width of worm; B, dorsal view of anterior region; C, lateral view of anterior region; D, dorsal view of posterior end with triple anal cirri; E, maxillae; F, mandibles; G, left parapodium 16, anterior view; H, right parapodium 100; I, limbate chaeta, left parapodium 28; J, pectinate chaeta, right parapodium 20; K, compound falciger, left parapodium 16; L, acicula, left parapodium 46; M, subacicular hook, left parapodium 46. A – I, K – M from specimen NMNS 6992 - 9; J from specimen NMNS 2572 - 122. Scale bars: A, 20 mm; B – C, 5 mm; C, 0.5 mm; D – E, 2 mm; G – H, 0.5 mm; I – M, 0.05 mm

FIGURE 4. Regressions of compared parameters of Eunice dilatata Grube, 1877 collected in the present study. A, relationship between body size and maximum number of branchial filaments of 18 specimens; B, relationship between body size and chaetiger number with first subacicular hooks of 18 specimens; C, relationship between body size and chaetiger number with first branchiae present of 18 specimens.