Luidia difficilis Li, 2006, new species
Creators: name: Li, Wei Liu Yulin Liao Xinzheng
Publisher: name: Zenodo
Year: 2006
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Asteroidea
Paxillosida
Luidiidae
Luidia
Luidia difficilis

description: Luidia difficilis, new species   
(Figs. 1-2)  
  Material examined. –  Holotype – CN IOCAS-E 1108, Beibu Gulf, [19º32'N 106º30'E], 32 m, sand, AT, 15 Apr.1962.   
 Paratype – 1 example, CN IOCAS-E 1109, same locality and date as holotype.   
  Diagnosis. –  Arms 6. Large abactinal paxillae squarish or rectangular, with 3-20 fine central granules and 10-20 peripheral spinelets. Most lateral spines are less than a millimeter in length, flattened and obliquely appressed on the inferomarginal plates. Adambulacral armature consists typically of 1 large furrow spine and 3 large spines on surface of plate. Pedicellariae is absent at oral end of mouth-plates. Ventrolateral plates with large tricuspid pedicellariae.   
  Description. –  Arms 6. R= 79.2 mm; r= 9.7 mm; br= 10.5 mm; R/r =8.2. Disk relatively small and arms slender. Marginal paxillae representing superomarginals squarish or rectangular and similar to adjacent abactinal paxillae. Paxillae in 5 longitudinal series on each side of arm; squarish or rectangular, with sides proximately 0.6-0.8 mm wide and 0.9- 1.0 mm long. At the arm base such series increased to 6. Side rows above mentioned form lateral borders of arms. Spherical surface of paxillae covered with 3-20 fine central granules about 0.2mm high and 0.17mm wide, 10-20 peripheral column spinelets and several intermediate spines between centrals and peripherals. Centrals short, rounded and granuliform, peripherals much more slender and subequal to centrals in length. Adjacent to lateral paxillae series are 5 more series, somewhat irregular, little rounded and smaller. Near the tips of arms, paxillae still smaller and less regularly arranged. Arms fairly high at base, about 10 mm, and disc higher than arms.   
Inferomarginals relatively short and wide, and coincident with adambulacrals. About 10 plates in 9.5 mm of arm-length, while their width is about 2.5 mm. Surface well covered with longitudinal rows of squamiform spines and a large number of much smaller spinelets. Abactinal row of spines larger, sometimes 1-2 spines subequal to the lateral one; actinal row of spines smaller. The largest spine situated on outer end of the plate is obliquely appressed on the plate and indistinct in dorsal view. Most are less than a millimeter in length, wide at base but gradually attenuate to an acute tip; close to it, but sometimes below, is a second spine of subequal size, and still further abactinally are spinelets similar to those of the abactinal paxillae but larger and more pointed. Along the margin of inferomarginals is a series of small spinelets. The fasciolar grooves covered in the inner part with capillary spinelets. At and near interbrachial angle the spines and spinelets much more slender and acute.  
Adambulacrals coincident with inferomarginals and ventrolaterals and present a wedgeshaped edge towards ambulacral furrow. Rarely one adambulacral plate coincident with 2 ventrolaterals and 2 inferomarginals. The armature consists typically of four spines. The first one, laterally compressed, curved, and hookshaped, lies well within furrow; about 0.8 mm long and 0.3 mm wide at the base. The second one, largest, also lightly curved, but much more stout and somewhat triangular in cross-section; about 1.2 mm long and 0.4 mm wide at the base. Then follows the third and fourth, straight and of proximately coniform with blunt tips, about two-thirds the length of second one; the two in a line parallel to the furrow, and a notch present at the base on the inner side facing furrow. On outer side of large spines may be 8 smaller spines varying in length and in shape. First and subsequent 2-7 adambulacrals with somewhat different armature from the rest. The armature of first consists of about 7 large spines; subsequent 2-7 adambulacrals with 1-2 furrow spines and 4-5 larger spines on the surface of plates.  
Mouth-plates somewhat narrow and long with an interspace covered over with a membrane. The most characteristic point in the armature of mouth-plates is the absence of any pedicellariae at oral end of plates. About 12 large spines in a series along main ridge of plate, much larger at the oral end. Secondary ridge of plate bearing about 8 much smaller spines, which become smaller towards distal part of the plate. Facing first adambulacral plate about 10 spinelets are found at the outer side of spines on the main ridge. Usually a series of about 9 subequal but much shorter spinelets on the side of each oral plate, deep in the mouth.  
Ventrolateral plates very small, and 2 or 3 plates situated in each interradial area between mouth plates and first inferomarginals. Each plate with about 8-20 slender spinelets, which are similar to those on outer part of adambulacrals. Subsequently are series of 3-4 pairs plates on each side, only a series of plates extending to the tip of arms, and becoming somewhat indistinct in distal part owing to their fusion with inferomarginals. Most plates have one large pedicellariae with 3 long and slender jaws, which are thicker and obtuser than peripheral spinelets. Similar pedicellariae have not been found elsewhere. On dry ray of paratype, with surface cleared, the plates at proximal base of ray large and triangular, bearing granule prominence at the top.  
Terminal plates relatively small, usually colourless. Madreporite completely hidden from view by surrounding paxillae, which are similar to adjacent ones, so difficult to distinguish.  
  Body colour. –  Color in alcohol preserved specimens very similar to that of L. hexactis and L. maculata. Oral surface very light, proximally fawn; dorsal surface light buff blotched and marked with large irregular dark areas.   
  Etymology. –  From Latin difficilis, to imply the species was difficult to align to any described species of Luidia.   
  Remarks. –  This is a very well marked species for while it seems to belong to Luidia alternata group of Döderlein (1920). By comparison the seven species of Luidia in the China seas (Chang, 1948; Chang et al., 1964; Liao & Clark, 1995), eight shallow-water Luidia species from the Indo-West Pacific (Clark & Rowe, 1971), 10 species of Luidia from the South China Sea (Lane et al., 2000), and five species of Luidia from New Zealand (Clark & McKnight, 2000), we found that L. difficilis, new species superficially resembles L. hexactis Clark, 1938 (type locality near the Montgomery Reef) and L. maculata Müller and Troschel, 1842 (type locality Southern Japan). The diagnostic characters that distinguish L. difficilis from L. hexactis and L. maculata are listed in Table 1. The characters of L. hexactis are according to the descriptions and illustrations of Clark (1938: 73-74, Pl. 17 Fig. 1) and Clark & Rowe (1971: 43); the characters of L. maculata are according to the descriptions and illustrations of Sladen (1889: 327), Fisher (1919: 163, 168), Döderlein (1920: 262, Pl. 18 Figs. 4, 13, Pl. 19 Fig. 16, Pl. 20 Figs. 23, 24) and Hayashi (1973: 48, Pl. 7 Fig. 4), and also based on the specimens as follows:   
 Comparative material. – Luidia maculata Müller & Troschel, 1842: 1 example, CN Q47 B-9, [18º15'N, 109ºE], muddy sand, AT, coll. Fan, 11 Apr.1959; 1 example, CN K51 B-7, [20ºN 112ºE], muddy sand, AT, coll. Ma, 3 Jul.1959; 1 example, CN K124 B-3, [20ºN 112º30'E], muddy sand, AT, coll. Qu, 8 Feb.1960; 1 example, CN N155 B-27, [18ºN 109ºE], sand, 32.5 m, AT, coll. Liu, 12 Mar.1960; 1 example, CN Q162 B-68, [21º22'N 109ºE], sand, 12 m, coll. Sun, 17 Feb.1960; 3 example, CN N207 B-120, [18º15'N, 109º15'E], muddy sand, 24 m, AT, coll. Shen, 14 May.1960; 1 example, CN X215 B-63, [20º22'N 109º38'E], sand, 32 m, 22 Apr.1962; 1 example, CN X277 B-38, [19ºN 106º30'E], sand, 43 m, 11 Oct.1962.
description: Published as part of Li, Wei Liu Yulin Liao Xinzheng, 2006, A New Sea-Star Species (Asteroidea: Luidiidae) From The South China Sea, pp. 441-445 in Raffles Bulletin of Zoology 54 (2) on pages 442-444, DOI: 10.5281/zenodo.13245454