A new species of Amphictene (Annelida, Pectinariidae) from the northern South China Sea

Abstract Pectinariids are a family of polychaetes commonly found in shallow coastal waters around the world, but their diversity is poorly known along the coasts of Asia. Here we describe Amphictene alata sp. n. (Pectinariidae), based on 15 specimens collected from the coastal waters of Guangdong in the northern South China Sea. This new species can be distinguished from all other 13 described species and one described subspecies of Amphictene by having a pair of dorsolateral lobes on segment 3, a pair of large lateral lobes on segment 21, and more scaphal hooks (26 to 37 pairs).


Introduction
Pectinariids, commonly called ice cream cone worms, are morphologically unique polychaetes with a cone-shaped tube which they build from sand grains, and a set of golden opercular paleae which they use for digging into soft sediment (Hartman 1941;Wolf 1984;Hutchings 2000;Rouse and Pleijel 2001). Currently five genera (Amphictene, Pectinaria, Cistenides, Lagis and Petta) are recognized in the family Pectinariidae (Fauchald 1977;Wolf 1984;Hutchings and Peart 2002).
Amphictene can be distinguished from other genera of Pectinariidae by having a cirrate dorsal opercular rim. Currently this genus has 13 recognized species and one recog-nized subspecies (Hutchings and Peart 2002;García-Garza and de León-González 2014). Among them only three species have been described from Asia: A. moorei (Annenkova, 1929) from the east coast of Russia, A. japonica (Nilsson, 1928) from Japan and A. leioscapha (Caullery, 1944) from Indonesia. The diversity of Pectinariidae is poorly known along the coasts of China, with only seven recorded species, some of which are South African or European species whose identities should be confirmed (Yang and Sun 1988;Sun and Qiu 2012). Here we describe a new species of Amphictene based on specimens collected from the coastal waters of Guangdong in the northern South China Sea.

Material and methods
Specimens were collected during benthic ecology surveys conducted in Daya Bay and Honghai Bay of the northern South China Sea (Table 1). Sediment samples were collected using a 0.05 m 2 or 0.1 m 2 van Veen grab, and washed through a sieve with a 0.5 mm mesh size. Specimens were picked up from the sieve, fixed in 5% formalin and later transferred to 70% ethanol. Specimens were observed under a Carl Zeiss Stemi 2000-C dissecting microscope fitted with an AxioCam ICc 1 camera. Two paratypes were dehydrated using a Xiangyi CFD-10D freeze-dryer, gold coated with an EDT SC-150, and observed under a TESCAN CEGA 3 scanning electron microscope. Types are deposited in the following institutions: the Australian Museum, Sydney, Australia (AM); The Marine Biological Science Museum of the Chinese Academy of Sciences, Qingdao, China (MBM); The South China Sea Institute of Oceanology of the Chinese Academy of Sciences, Guangzhou, China (SCSMBC). The taxonomic terms defined by Hutchings and Peart (2002) are used for describing the species.

FAMILY
Diagnosis. Cephalic veil completely free from operculum forming dorsal semicircle around numerous peristomial palps. Rim of cephalic veil with 11 to 16 long cirri. Dorsal operculum raised with 20-25 marginal cirri. Comb-like branchiae present on segments 3 and 4. A pair of dorsal lateral lobes present on segment 3. Chaetigers 1 to 3 (segments 5 to 7) with notopodia and notochaetae only. Chaetigers 4 to 16 (segments 8 to 16) biramous with notopodia, neuropodia, notochaetae and neurochaetae. Notochaetae winged capillaries. Neurochaetal uncini with major teeth arranged in two to three rows. Segment 21 with a pair of large lateral lobes but without chaetae. Scaphe distinctly separated from abdomen, with 26-37 pairs of short hooks with a slightly curved tip.
Segments 5 to 7 (chaetigers 1 to 3) with notopodia and notochaetae only (Figs 1B, 2F); anteroventral lobe large and broad (Figs 1A, 2E, 3B). Segment 5 with a small mid- ventral lobe, and a pair of huge lateral ventral lobes covering much of the venter. Segment 6 with a small midventral lobe, and a pair of larger lateral ventral lobes. Segment 7 with a raised ventral lobe running through the venter. Segments 8 to 20 (chaetigers 4 to 16) biramous with wedge-shaped notopodia and lobe-shaped neuropodia. Notopodia with two kinds of simple chaetae: one slender, with sub-distal serrations along one side (Figs 1D, 3F-I); the other stout, with finely hirsute surface on one side, tapering    to an acute tip (Figs 1E, 1F, 3J). Neuropodia with uncini arranged in one row along raised ridge of the tori. Uncini with two or three longitudinal rows of teeth, each row with 7 to 9 major teeth (Figs 1G, 3K-O). Segment 21 achaetous, with a pair of large lobes covering much of the lateral sides of the body (Figs 1C, 2G, 3P).
Tube yellowish, conical, straight, composed of sand grains and shell fragments held together by cement ( Fig. 2A).
Variation in morphological characters. A number of morphological characters exhibit variations (Table 1). Specifically, the body length ranges from 10.2 to 50.7 mm, the widest width of anterior body ranges from 2.2 to 6.9 mm, the numbers of cephalic veil cirri range from 11 to 16, the pairs of paleae range from 8 to 11, the number of triangular lappets on the raised opercular rim varies from 20 to 25, and the number of pairs of scaphal hooks ranges from 25 to 37. The widest width of anterior body (BW) and body length (BL) are positively correlated: BL = 0.7469BW -3.6038, R 2 = 0.8252, P < 0.001, n = 15. Correlational analysis between BW, which is considered to be less affected by fixation than BL, and other quantitative parameters in Table  1 shows that BW had significant positive correlation only with the number of scaphal hooks (SH): SH = 2.3185BW + 20.213, R 2 = 0.3419, P = 0.036, n = 13.
Type locality and distribution. Currently only known from Daya Bay and Honghai Bay, Guangdong in the northern South China Sea.

Discussion
Amphictene alata sp. n. can be distinguished from other currently recognized species in the genus by several features. First, it has a pair of dorsolateral lobes with crenulated margins on segment 3. None of the other species has dorsolateral lobes. Second, segment 21of A. alata sp. n. has a pair of large lateral lobes but has no chaetae. Among the reported species of Amphictene, A. japonica is also achaetous in segment 21, but it does not have large lateral lobes. Third, A. alata sp. n. has more scaphal hooks (26-37 pairs) than other species of Amphictene (4 to 25 pairs). Forth, the scaphal morphology of A. alata sp. n. is unique among Amphictene spp. in having 2 pairs of lateral lappets, four small triangular terminal lappets, and an oval anal plate with a smooth margin.