Description of two new species of Neotachidius Shen & Tai, 1963 (Copepoda, Harpacticoida, Tachidiidae) from Korean brackish waters and proposal of a new genus for Tachidius (Tachidius) vicinospinalis Shen & Tai, 1964 Author Huys, Rony Author Ohtsuka, Susumu Author Conroy-Dalton, Sophie Author Kikuchi, Yoshiaki text Zoological Journal of the Linnean Society 2005 2005-01-28 143 1 133 159 http://dx.doi.org/10.1111/j.1096-3642.2004.00148.x journal article 3534 10.1111/j.1096-3642.2004.00148.x 16ebf94a-9ae1-4744-ac41-2bfa923ee3f5 0024-4082 5684683 NEOTACHIDIUS PARVUS SP. NOV. Synonym: Tachidius (Neotachidius) triangularis Shen & Tai, 1963 sensu Song & Chang (1995) [partim]. Type material: Holotype ♀ ( NMNH reg. no. 251942) dissected and mounted on slides . Paratypes deposited in NMNH are 2 ♀♀ (reg. no. 251943–944) and 3 ♂ (reg. nos. 251945–947) dissected and mounted on slides; 20 ♀♀ and 20 ♂♂ in alcohol (reg. no. 251973). Paratypes deposited in NHM are 1 ♀ dissected on ten slides (reg. no. 2003.808), 1 ♂ dissected on seven slides (reg. no. 2003.809); 24 ♀♀ and 13 ♂♂ in alcohol (reg nos. 2003.771–807) Type locality: Stn five in a small river discharging into Kwangyang Bay , South Korea (34∞57.1¢N, 127∞36.4¢E), salinity 11.10‰ (see Ohtsuka et al., 1992 ) . Additional material: (1) Taehwa River estuary, Ulsan , South Korea ; leg. C.Y. Chang , 31 January 1987 ; 1 ♀ and 1 ♂ in alcohol ( NHM reg. nos. 2003.812–813). (2) Jochean, Cheju Island , South Korea ; leg. C.Y. Chang and S. J. Song , 27 October 1993 ; 2 ♀♀ in alcohol ( NHM reg. nos. 2003.810–811) . Body length: ♀ : 500 ± 30 mm ( N = 53); ♂ : 450 ± 30 mm ( N = 53; based on paratypes ). Neotachidius parvus is closely related to N. coreanus and the description below is consequently restricted to differences only. Description Based on NHM paratypes (reg. nos. 2003.771–809). Female: Spinules around posterior margin of cephalosome and somites bearing P2–P3 shorter than in N. coreanus ( Fig. 11A ). Slight differences in fine surface spinulation of pedigerous somites as illustrated in Figure 11A . Rudimentary tergite of P1-bearing somite less well defined. Posterior margin of P4-bearing somite denticulate laterodorsally but smooth dorsally; dorsolateral spinules shorter than in N. coreanus . P5- bearing somite with spinules around lateroventral corner of pleurotergite; lateral surface spinules distinctly shorter and more blunt than in N. coreanus ( Fig. 11C ). Dorsal posterior margins of genital double-somite and free abdominal somites 2–3 denticulate instead of with long spinules ( Fig. 11A, C ); spinules along ventral posterior margin of these somites shorter than in N. coreanus ( Fig. 11B ). Paired spinule rows posterior to genital slit absent (compare with N. coreanus : Figs 1B , 2C ); remaining two rows consisting of smaller spinules ( Fig. 11B, C ). Genital field area less raised in lateral aspect ( Fig. 11C ). Lateral surface ornamentation of genital double-somite less elaborate than in N. coreanus ( Fig. 11C ). Anal somite with paired laterodorsal spinule rows but without spinules dorsally ( Fig. 13D ). Anal operculum spinulose but spinules markedly shorter than in N. coreanus . Caudal rami ( Figs 11B , 13D ) slightly longer than wide but shorter than in N. coreanus ; armature and ornamentation essentially as in N. coreanus , except dorsolateral spinule row (arrowed in Fig. 10D ) absent. Antennule ( Fig. 12A ) with short apical segment, only slightly longer than segment 6. Armature as in N. coreanus . Antenna ( Fig. 12B ) with spinule rows on abexopodal margin of basis and proximal endopod segment. Exopod distinctly 2-segmented; exp-1 shortest, with one long slender plumose seta; exp-2 with short smooth seta fused to lateral margin and two unequal plumose setae apically; spinular ornamentation around outer distal corner of exp-2 more elaborate than in N. coreanus . Distal endopod segment laterally with one unipinnate spine in proximal third and one smooth seta plus one unipinnate spine in middle third. Apical armature of enp-2 consisting of one unipinnate spine and four geniculate setae; longest geniculate seta with few spinules and fused at base to short naked seta; segment with various spinule rows and surface frills as figured. Figure 11. Neotachidius parvus sp. nov. (♀) A, habitus, dorsal; B, urosome (excluding P5-bearing somite), ventral; C, P5-bearing and genital double-somite, lateral (P5 omitted). Figure 12. Neotachidius parvus sp. nov. A, segment contours of ♀ antennule; B, antenna ♀; C, P1 ♀, anterior (outer distal seta of enp-3 arrowed); D, P3 ♀, anterior (proximal part of protopod and most ornamentation omitted); E, P3 ♂, anterior (proximal part of protopod omitted). Mandible. Palp with similar armature as in N. coreanus . Endopod with spinule row on anterior surface (arrowed in Fig. 5D ). Maxillule, maxilla and maxilliped as in N. coreanus . P1 ( Fig. 12C ). Most spinules on anterior surface of praecoxa and coxa and around distal margin of basis distinctly shorter than in N. coreanus . Inner basal seta more slender and longer, reaching beyond distal margin of enp-2. Rami as in N. coreanus except for inner distal element of enp-3 (arrowed in Fig. 12C ) being long, plumose and setiform instead of pinnate and spiniform. P2–P4 ( Figs 12D , 13A ) as in N. coreanus except for (a) intercoxal sclerites with spinules anteriorly but not posteriorly; (b) long spinules on anterior surface of coxa absent; (c) spinules around distal margin of basis uniform in size; (d) posterior spinules on P4 coxa absent, and (e) P4 exp-3 with only one spinule row on posterior surface. P5 ( Fig. 13C ) longer and with outer concavity less pronounced than in N. coreanus ; about 1.40 times as long as maximum width; spinule pattern on anterior surface and along inner margin different (as illustrated in Fig. 13C ); apical seta smooth instead of plumose; spines more slender than in N. coreanus . Male. Sexually dimorphic in size, urosome ornamentation, antennule, P2 endopod, P3 exopod, P5 and P6. Antennule ( Figs 14A , 15A–D ) as in N. coreanus except for two differences on segment 6: (a) multicuspidate process ( Figs 14A , 15B; b in Fig. 15D ) less pronounced and typically with five cusps, and (b) cylindrical process adjacent to longitudinally ribbed element (a in Fig. 15D ) with two spinulose elements (ventralmost smooth in N. coreanus ; arrowed in Fig. 14D ). Armature formula: 1-[1 pinnate], 2-[1 pinnate], 3-[6 bare +5 pinnate], 4-[6 bare +2 pinnate + ae], 5-[2 pinnate], 6-[8 bare +4 pinnate +1 striated element + (1 + ae)], 7-[12 +2 modified + acrothek]. P2 endopod ( Figs 13B , 16B ). Enp-1 comparatively longer than in N. coreanus with outer distal corner not spinous; spinules along outer margin longer, those of inner distal corner shorter than in N. coreanus . Middle segment transversally enlarged but markedly shorter than in N. coreanus ; outer margin distinctly convex; both inner setae markedly shorter than in N. coreanus . Enp-3 small ( Fig. 16B ), with row of long setules on anterior surface covering spinous apophysis of enp-2; outer distal seta strongly reduced, represented by a short and blunt, basally fused element (arrowed in Fig. 13B ). P3 exopod ( Fig. 12E ) more robust than in N. coreanus , with exp-2 being distinctly shorter; inner setae of exp-3 shorter. P3 endopod about as long as in N. coreanus but enp-3 proportionally longer. P5 ( Fig. 14B, C ) medially fused with medial incision more pronounced than in N. coreanus ; each with three serrate spines and two naked setae; middle and inner spines shorter than in N. coreanus ; anterior surface spinules absent; spinules around midventral distal margin coarser than in N. coreanus . P6 ( Fig. 14B, C ) symmetrical; each member with two serrate spines and naked outer basal seta; spinules around medial distal margin uniform in size and coarser than in N. coreanus . Ornamentation of urosome essentially as in N. coreanus except for size of spinules ( Fig. 14B, C ). Variability: The females from Cheju Island were larger in size ( 575–579 mm ). Etymology: The specific name is derived from the Latin parvus , meaning small, and alludes to the small size of the present species.