A new species of Pectinaria (Annelida, Pectinariidae), with a key to pectinariids from the South China Sea

Abstract Pectinariidae is a family of polychaetes building unique ice-cream cone shaped sandy tubes. Pectinaria torquata sp. n. (Pectinariidae) is described from the coastal waters of the northern South China Sea. This new species can be distinguished from all other 25 recognized species in the genus by a combination of characters: 16 chaetigers; 26–32 cirri in the cephalic veil; 11–12 pairs of cephalic spines; uncini with major teeth arranged in two rows, each with 7–8 major teeth; presence of a dorsal posterior lobe on segments 2 and 20; 4–5 pairs of curved scaphal hooks; and an anal flap with a crenulated margin. A key to all recognized pectinariids in the South China Sea is provided.


Introduction
Pectinariidae is a family of polychaetes commonly found in the soft bottom of coastal shallow waters. They are easily recognized by their unique ice-cream cone shaped sandy tube, and two bundles of golden thick chaetae called paleae on the first segment which they use for sediment digging (Fauchald 1977, Wolf 1984. There are 50 recognized species of Pectinariidae in five genera: 15 species of Amphictene Savigny, 1818; six species of Cistenides Malmgren, 1866; ten species of Lagis Malmgren, 1866; 25 species of Pectinaria Savigny, 1818; and four species of Petta Malmgren, 1866 (Hartman 1941, Hutchings and Peart 2002, Sun and Qiu 2012, García-Garza and de León-González 2014, Nishi et al. 2014, Wong and Hutchings 2015, Zhang et al. 2015. Ten species of Pectinariidae have been recorded from the South China Sea, including four species of Amphictene, three species of Lagis, and three species of Pectinaria (Wu and Chen 1985, Yang and Sun 1988, Paxton and Chou 2000, Sun and Qiu 2012, Salazar-Vallejo et al. 2014, Zhang et al. 2015, Glasby et al. 2016. Pectinaria can be distinguished from other genera of Pectinariidae by a combination of characters: smooth opercular rim; cephalic veil free with numerous cirri; and neurochaetal uncini having major teeth arranged in two or more rows (Wong and Hutchings 2015). Here a new species of Pectinaria is described, based on three specimens collected from the coastal waters of the northern South China Sea.

Materials and methods
Specimens were collected while undertaking a benthic ecology monitoring program of the South China Sea Environmental Monitoring Center (SCSEMC), State Oceanic Administration. Benthic samples were collected from the northern South China Sea using a 0.05 m 2 van Veen grab, and rinsed through a sieve with 0.5 mm mesh size. Samples retained on the sieve were collected, fixed in 5% formalin, and later transferred to 70% ethanol. Type specimens are deposited at the Institute of Oceanology, Chinese Academy of Science (IOCAS), Qingdao. Specimens were examined under a Carl Zeiss Stemi 2000-C dissecting microscope. Morphological features were recorded using a Carl Zeiss AxioCam ICc 1 digital camera attached to the microscopes. A paratype was freeze-dried using a Xiangyi CFD-10D, gold coated using an EDT SC-150, and examined under a TESCAN CEGA 3 scanning electron microscope (SEM). Line drawings were made using a Wacom Intuos Pro Pen and Touch Large Tablet.
The taxonomic terms defined by Hutchings and Peart (2002) were used in the species description.
incomplete specimens of similar sizes, intraspecific variation amongst these morphological characters may have been underestimated. Type locality and distribution. Currently only known from Daya Bay (Guangdong Province) and Beibu Gulf (Guangxi Province) in the northern South China Sea.
Remarks. Pectinaria torquata sp. n. can be distinguished from the other 25 described species of Pectinaria by several features (Table 1). First, it has a dorsal posterior lobe on segment 2, which is unique among the described species of Pectinaria species. This structure is prominent in the type specimens, and does not change by preservation. Second, P. torquata sp. n. has a dorsal posterior lobe on both segment 20 and 21, a feature that has not been reported from any other recognized species in this genus (Hartman 1941, Long 1973, Hutchings and Peart 2002, Nishi et al. 2014, Wong and Hutchings 2015. Third, P. torquata sp. n. has only 4-5 pairs of small blunt scaphal hooks, which is fewer than those in most described species. Fourth, the anal flap lacks a middorsal anal cirrus with a crenulated margin. There are eight species in which the dorsal posterior lobe on segment 2 is not recorded (Table 1). Except for Pectinaria dimai Zachs, 1933 and Pectinaria panava Willey, 1905 for which the middosal anal cirrus is not described, the other five species have a middorsal anal cirrus; P. torquata sp. n. lacks a middorsal anal cirrus (Table  1). Furthermore, it differs from P. dimai which has 3-4 rows of major teeth on each uncinus, and 6-7 teeth per row; P. torquata sp. n. has 2 rows of major teeth, and 7-8 teeth per row. Pectinaria panava has more scaphal hooks than P. torquata sp. n.
A key to eleven species of Pectinariidae, including P.torquata sp. n., that have been recorded from the South China Sea in the literature is provided below (Wu and Chen 1985, Yang and Sun 1988, Paxton and Chou 2000, Sun and Qiu 2012, Salazar-Vallejo et al. 2014, Zhang et al. 2015, Glasby et al. 2016. The genera Petta and Cistenides have not been recorded in the South China Sea.