Journal 
INTRODUCTION
The family Pterasteridae Perrier, 1875 of order Velatida Perrier, 1884 contains eight genera, of which the genus Diplopteraster Verrill, 1880 comprises seven species including D. clarki (Bernasconi, 1937), D. hurleyi (McKnight, 1973), D. multipes (M. Sars, 1866), D. otagoensis (McKnight, 2006), D. peregrinator (Sladen, 1882), D. semireticulatus (Sladen, 1882), and D. verrucosus (Sladen, 1882) (Mah, 2016). Diplopteraster can be distinguished from other genera in this family by its two alternating arrangements of adambulacral spines united by a web skin, enlarged central paxillar spines surrounded by peripheral spines, and webbed oral spines of each jaw (Clark and Downey 1992). D. multipes is usually similar in pentagonal stellate body shape to almost every other species of genus Diplopteraster, but is distinguished by having protruded spines, and by not being commonly found in shallow water (Lambert 2000). D. multipes shares a very close similarity to D. verrucosus (Fisher 1911). The key taxonomic difference from other Diplopteraster species is the number of spiracles in the supradorsal membrane, of which D. multipes has more than eight, while D. verrucosus has four or five, and D. peregrinator has two or three. It also differs from other Diplopteraster species by having a regularly reticulated and distinct muscle band (Fisher 1911), which is slightly visible (as in D. hurleyi), and closely reticulated (as in D. otagoensis) (Mcknight 2006). Fisher (1911) recorded D. multipes from the Arctic Ocean to San Diego, California at 150 to 1170 meters and from North Atlantic at 140 to 1060 meters. It is reported in the Atlantic, from the Arctic to Chesapeake Bay, southwest of Ireland, and off the coast of South Africa at 91 to 1225 meters by Clark and Downey (1992). Lambert (2000) found this species in Puget Sound at 57 to 1171 meters. This peculiar species is also distributed in the North Pacific, specifically in Japan at 923 to 1093 meters (Hayashi 1940), in Okhotsk Sea, and near the Aleutian Islands at depths of 90 to 1170 meters (D’yakonov 1968). D. multipes is known for its worldwide distribution.
MATERIALS AND METHODS
Asteroid specimens were collected by trawling nets on 05 November 2016 from the Korea Strait (33°41′N, 127°26′E). The collected specimens were preserved in 95% ethanol, and their morphological characteristics such as size of disk, dorsal spines, arrangement of adambulacral and oral spines were observed. Morphological features of the specimen were photographed using a digital camera (Nikon D7000, Nikon Co., Tokyo, Japan) and stereomicroscope (Nikon SMZ1000). The identification of the specimen was mainly based on the descriptions of Hayashi (1940), Clark and Downey (1992), and Lambert (2000).
SYSTEMATIC ACCOUNTS
Class Asteroidea de Blainville, 1830
Order Velatida Perrier, 1884
Family Pterasteridae Perrier, 1875
Genus Diplopteraster Verrill, 1880
Key to the Korean genera of family Pterasteridae
-
Muscle band of supradorsal membrane irregularly reticulated and not distinct (Fig. 2A), not alternating adambulacral plates (Fig. 2B) ········································ Pteraste
-
Muscle band of supradorsal membrane regularly reticulated and distinct (Fig. 1D), alternating adambulacral plates (Fig. 1G) ········································· Diplopteraster
Diplopteraster multipes (M. Sars, 1866)
Pteraster multipesM. Sars, 1866, p. 200.
Retaster multipesSladen, 1889, p. 477.
Diplopteraster multipes: Fisher, 1911, p. 371, pl. 107, figs. 1, 2; Clark, 1923, p. 300; Hayashi, 1940, p. 199, pl. 12, Fig. 1, pl. 13, Fig. 1; Clark, 1952, p. 198; D’yakonov, 1968, p. 67; Clark and Courtman-Stock, 1976, p. 82, Fig. 68; Clark and Downey, 1992, p. 311, pl. 75G; Lambert, 2000, p. 92, Fig. 71; Mah, 2016, 124128.
Material examined. Two specimens, Korea Strait (33°41′N, 127°26′E), 05 November 2016, Bae and Kim, at 93 m depth by trawling nets.
Description. Body plump, pentagonal, stellate shape. Arms five in number, broad, and short (R/r=1.4), with dorsally recurved arm tips (Fig. 1A, B). Dorsal surface tough, bearing central spine of each paxilla surrounded by peripheral spines and protruded through supradorsal membrane. Paxilla slender, surrounded by more than eight spiracles, with reticulated visible muscular bands (Fig. 1C, D). Osculum surrounded and covered with numerous stubby spines (Fig. 1E). Oral plate bearing four to six slender spines (Fig. 1F). Slender sub-oral spines located behind and longer than oral spines, with two series of spines connected with a common membrane. Ventrolateral spines long, slender, and arranged perpendicularly in adambulacral groove. Adambulacral plates alternate from three to four and four to five spines, webbed together into a comb (Fig. 1G). Tube feet strong, forming sucking discs (Fig. 1H).
Size. R=21 mm, r=15 mm, R/r=1.4.
Color. Yellowish brown in life.
Habitat. Muddy and sandy areas.
Distribution. Korea (Korea Strait), Pacific (Suruga, Japan to Puget Sound - San Diego, California), Okhotsk Sea, Aleutian Islands, Bering Sea, Arctic, Atlantic (Chesapeake Bay to southwest of Ireland), Barents Sea, Argentina, South Africa.
Deposition. Collected specimens deposited in the Marine Echinoderm Resource Bank of Korea (MERBK), Sahmyook University, Seoul, Korea.
Remarks. This species was originally described as Pteraster multipes (M. Sars, 1866) and revised to Diplopteraster multipes by Verrill (1880). Some Pteraster species such as P. militaris and P. tesselatus which were reported in Korea (Shin and Rho 1996; Shin and Kim 2016) were commonly found in shallow water, but D. multipes was usually collected from deep waters (Fisher 1911; Hayashi 1940; D’yakonov 1968; Clark and Downey 1992; Lambert 2000). D. multipes possesses muscle bands that are not present in P. militaris and P. tesselatus. The shape of D. multipes resembles that of almost every other Diplopteraster species with respect to the presence of protruding spines through its supradorsal membrane. Some specific key characters of P. tesselatus such as supradorsal membrane (Fig. 2A) and the arrangement of the adambulacral spines (Fig. 2B) were compared to our D. multipes specimen. The key characteristics of D. multipes were the presence of muscle bands (Fig. 1C, D) in the supradorsal membrane, the number of spiracles located in this membrane (Fig. 1D), and the number of alternating adambulacral spines (Fig. 1G). The other descriptions of important characters of our specimen are in accord with those of Fisher (1911), Clark and Downey (1992), and Lambert (2000), except for the number of tube feet rows. Our specimen possessed two rows of tube feet (Fig. 1H), whereas other species of the genus Diplopteraster generally possess four rows. According to Mcknight (2006), tube feet of the genus Diplopteraster were usually arranged in four rows, at least in adult specimens. Therefore, our specimen seems to be still young. This study represents the first report of the genus Diplopteraster and Diplopteraster multipes in Korean fauna.
