Neotachidius, 2005

Huys, Rony, Ohtsuka, Susumu, Conroy-Dalton, Sophie & Kikuchi, Yoshiaki, 2005, 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, Zoological Journal of the Linnean Society 143 (1), pp. 133-159 : 147-150

publication ID	https://doi.org/ 10.1111/j.1096-3642.2004.00148.x
DOI	https://doi.org/10.5281/zenodo.5700765
persistent identifier	https://treatment.plazi.org/id/038387C0-FF86-FFEE-7B97-FAF7FB8874F3
treatment provided by	Carolina
scientific name	Neotachidius
status	sp. nov.

Treatment

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 View Figure 11 ). Slight differences in fine surface spinulation of pedigerous somites as illustrated in Figure 11A View Figure 11 . 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 View Figure 11 ).

Dorsal posterior margins of genital double-somite and free abdominal somites 2–3 denticulate instead of with long spinules ( Fig. 11A, C View Figure 11 ); spinules along ventral posterior margin of these somites shorter than in N. coreanus ( Fig. 11B View Figure 11 ). Paired spinule rows posterior to genital slit absent (compare with N. coreanus : Figs 1B View Figure 1 , 2C View Figure 2 ); remaining two rows consisting of smaller spinules ( Fig. 11B, C View Figure 11 ). Genital field area less raised in lateral aspect ( Fig. 11C View Figure 11 ). Lateral surface ornamentation of genital double-somite less elaborate than in N. coreanus ( Fig. 11C View Figure 11 ). Anal somite with paired laterodorsal spinule rows but without spinules dorsally ( Fig. 13D View Figure 13 ). Anal operculum spinulose but spinules markedly shorter than in N. coreanus .

Caudal rami ( Figs 11B View Figure 11 , 13D View Figure 13 ) 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 View Figure 10 ) absent.

Antennule ( Fig. 12A View Figure 12 ) with short apical segment, only slightly longer than segment 6. Armature as in N. coreanus .

Antenna ( Fig. 12B View Figure 12 ) 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.

Mandible. Palp with similar armature as in N. coreanus . Endopod with spinule row on anterior surface (arrowed in Fig. 5D View Figure 5 ).

Maxillule, maxilla and maxilliped as in N. coreanus .

P1 ( Fig. 12C View Figure 12 ). 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 View Figure 12 ) being long, plumose and setiform instead of pinnate and spiniform.

P2–P4 ( Figs 12D View Figure 12 , 13A View Figure 13 ) 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 View Figure 13 ) 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 View Figure 13 ); 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 View Figure 14 , 15A–D View Figure 15 ) as in N. coreanus except for two differences on segment 6: (a) multicuspidate process ( Figs 14A View Figure 14 , 15B; b View Figure 15 in Fig. 15D View Figure 15 ) less pronounced and typically with five cusps, and (b) cylindrical process adjacent to longitudinally ribbed element (a in Fig. 15D View Figure 15 ) with two spinulose elements (ventralmost smooth in N. coreanus ; arrowed in Fig. 14D View Figure 14 ). 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 View Figure 13 , 16B View Figure 16 ). 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 View Figure 16 ), 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 View Figure 13 ).

P3 exopod ( Fig. 12E View Figure 12 ) 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 View Figure 14 ) 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 View Figure 14 ) 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 View Figure 14 ).

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.