Acartiella sinensis Shen and Lee, 1963

Srinui, Khwanruan & Ohtsuka, Susumu, 2015, Supplementary Description of Three Acartiella Species (Crustacea: Copepoda: Calanoida) from Estuarine Waters in Thailand, Species Diversity 20, pp. 167-181 : 175-179

Acartiella sinensis Shen and Lee, 1963

( Figs 7–9 , 10C )

Acartiella sinensis Shen and Lee, 1963 : pls 583–584, figs 30–40 (original description); Chen and Zhang 1965: pls 114–115, 51, figs 3–7; Zheng et al. 1982: pls 93–94, Fig. 54, a–e; Suwanrumpha 1987: pl 38, fig. 73 A–E; Pholpunthin 1997: pl 31, figs 8–15; Orsi and Ohtsuka 1999: pls

128–130; Pinkaew 2003: pls 8, 10, 23, 25–26, 62, 111, fig

7 a–e.

Material examined. Six females and 5 males, Bangpakong Estuary , Gulf of Thailand (station 2 in Fig. 1 ), July 22, 2012 (BIMS-Zoo-0265) .

Female. Total length 1.28–1.49 mm (1.36± 0.08 mm, N=11); prosome length 0.42–0.48 mm (0.45± 0.02 mm); prosome width 0.32–0.37 mm (0.34± 0.02 mm).

Body ( Fig. 7A, B ) similar to that of A. kempi , but armature slightly different and urosome asymmetrical; prosomal ends each with row of small spines. Genital operculum located midventrally ( Fig. 10C ); anal somite totally fused with both caudal rami; caudal rami each with six setae and distorted, with left ramus more severely twisted than right.

Antennule ( Fig. 8A ) similar to that of A. kempi , but right antennule incompletely 23-segmented; segments 2−5 partly fused, entire antennule curved toward ventral part of body. Armature elements as follows: 1=1, 2 (2−5)=4+ae, 3=2, 4=1+ae, 5=1, 6=0, 7=2+ae, 8=1, 9=1+(1 spiniform element), 10=1+(2 spiniform elements)+ae, 11=1+(2 spiniform elements), 12=1+(2 spiniform elements)+ae, 13=1+(2 spiniform elements), 14=1+(2 spiniform elements), 15=1+(2 spiniform elements), 16=1+(2 spiniform elements)+ae, 17=1+(2 spiniform elements)+ae, 18=1+(2 spiniform elements), 19=1, 20=2, 21=2, 22=2, 23=4+ae.

Antenna ( Fig. 7C ) similar to that of A. kempi , basis having thick-walled on both sides with row of fine hairs on outer margin, three plumose setae on inner margin, and fine hairs on inner edge in two groups separated by proximal two plumose setae; exopod completely fused with basis, having seven long plumose setae on tapered terminus; free endopodal segment with 10 setae.

Mandible ( Fig. 7D ) similar to that of A. kempi but armature consisting of two cuspidate teeth and three small teeth on gnathobase instead of two small teeth as in A. kempi ( Fig. 2E ); basis with inner seta just beyond midlength; first endopodal segment with short inner seta, second segment with one long seta, one medium long seta, and one short seta terminally; first exopodal segment fused to basis, with long inner distal seta, free exopodal segment with one long and two medium long setae.

Maxillule ( Fig. 7E ) similar to that of A. kempi except preacoxal arthrite bearing one strong, four medium thick, and three thin spinules on anterior surface; coxa with four setae on epipodite; exopod with three terminal setae.

Maxilla ( Fig. 7F ) endite with three long, one medium long, and three small setae; basis with one stout serrate seta; endopod with one small, one medium long and four long serrate setae.

Maxilliped ( Fig. 8B ): first syncoxal endite with one strong seta and one small seta; basis with row of fine spinules along both margins; endopod composed of two segments, with first segment bearing three small spines and second segment represented by inward-curving claw.

Legs 1–4 ( Fig. 8C–F ) similar to those of A. kempi but coxa and basis of leg 1 different, armed with small spinules along inner margin; first exopodal segment with small proximal spinules on outer margin and fine hairs along inner margin edge, second and third exopodal segments with fine hairs on outer margin; first exopodal segment of leg 2 and leg 3 with fine hairs on inner margin, second exopodal segments of leg 2 and leg 3 with fine hairs on both sides, third exopodal segments of leg 2 and leg 3 with fine hairs along outer edge; leg 4 with fine hairs along inner margin of basis and both side of first and second exopodal segments, third exopodal segments and first to second endopodal segments with fine setules along outer edge. Seta and spine formula as shown in Table 3.

Leg 5 ( Fig. 9A ) symmetrical; coxa unarmed, completely fused with intercoxal sclerite; basis with plumose outer seta; endopod 1-segmented, slightly curved inward and shorter than 1/3 of exopod, distal half serrate along outer margin; exopod represented by long, curved segment with small outer spine at mid-length, terminal end with both margins serrate.

Male. Total length 1.10–1.23mm (1.15± 0.04 mm, N=6); prosome length 0.71–0.76 mm (0.73± 0.01 mm); prosome width 0.23–0.24 mm (0.23± 0.004 mm).

Body ( Fig. 9B, C ) symmetrical; urosomite 5-segmented; caudal rami each with five plumose setae and one small seta.

Right antennule ( Fig. 9D ) geniculate, incompletely 20-segmented; segments 2–4 and 6–7 partly fused in dorsal view, segments 12–14 having rows parallel of small spines along length of segments. Armature elements as follows: 1=1, 2=(2–4)=4+ae, 3=1, 4=3+2+ae, 5=1, 6–7=(1 spiniform element)+ae, 8=(1 spiniform element), 9=(1 spiniform element), 10=2+ae, 11=1, 12=1+ae, 13=1, 14=1, 15=(1 process), 16=2+(1 process), 17=1+(1 spiniform element)+(1 process), 18=3+(1 spiniform element), 19=2+(1 spiniform element), 20=4+ae.

Legs 5 ( Fig. 9E ) asymmetrical and uniramous; both coxae fused. Right leg with single outer seta on basis; endopod completely fused with basis and expressed as triangular inner process on proximal to mid-length region; exopod 2-segmented, first segment about twice as long as wide, proximal end with prominent process bearing small seta at mid-length, irregularly sinuate along inner margin; second segment abruptly curved inward, tapering distally, with small seta near terminal end and superficially serrate seta terminally. Left leg with thickened basis completely fused with endopod, bearing prominent triangular process smoothly curved to hook-like tip, inner margin irregularly sinuate; exopod 2-segmented, first segment with small seta sub-terminally; second segment with hirsute region at proximal end, small, thick seta at middle of inner margin, and three terminal spines of unequal length.

Remarks. This species was originally described by Shen and Lee (1963) based on specimens collected from the northern Luichow Peninsula, East China Sea, where the body lengths of females and males were reported to be 1.38 and 1.23 mm, respectively. Further specimens described from the South China Sea ranged from 1.30 to 1.40 mm and 1.10 to 1.17 mm for females and males, respectively ( Chen and Zhang 1965); specimens introduced from China to the San Francisco Estuary, California, ranged from 1.27 to 1.64 mm and 1.17 to 1.34 mm for females and males, respectively ( Orsi and Ohtsuka 1999). The specimens of both sexes examined in the present study were similar to those from the South China Sea ( Chen and Zhang 1965).

The description of the female genital structure in the present study corresponds well with the observations of Barthélémy (1999), who studied the genital structures of six species of Acartiella but not A. kempi (see Fig. 10C ).

Distribution. This species has so far been recorded from the East China Sea ( Shen and Lee 1963; Shang et al. 2007), the South China Sea ( Chen and Zhang 1965), the Taiwan Strait ( Zheng et al. 1982), the upper Gulf of Thailand ( Suwanrumpha 1987; Pinkaew 2003), and Thale-Noi, southern Gulf of Thailand ( Pholpunthin 1997). A non-indigenous population was accidentally introduced via ballast water into San Francisco Bay, California, USA, where it became established prior to 1993 ( Orsi and Ohtsuka 1999). Acartiella sinensis was found to be abundant in brackish water of 18–21.8‰ in the East and South China Sea ( Shen and Lee 1963; Shang et al. 2007). In Thailand, the species was found to occur in waters of around 31.3°C and around 5.0‰ in July, 2012 (present study). In San Francisco Bay, the maximum abundance of this species was recorded in waters of 2.5–8.6‰ ( Orsi and Ohtsuka 1999).

Figures

Fig. 7. Acartiella sinensis Shen and Lee, 1963, female. A, habitus, dorsal view; B, habitus, lateral view; C, right antenna; D, right mandible; E, right maxillule; F, left maxilla.

Fig. 8. Acartiella sinensis Shen and Lee, 1963, female. A, right antennule; B, left maxilliped; C, right leg 1; D, right leg 2; E, right leg 3; F, right leg 4. Roman numerals in A indicate numbers of ancestral segments following Huys and Boxshall (1991).

Fig. 9. Acartiella sinensis Shen and Lee, 1963, female (A), male (B–E). A, legs 5; B, habitus, dorsal view; C, habitus, lateral view; D, right antennule; E, legs 5. Roman numerals in D indicate numbers of ancestral segments following Huys and Boxshall (1991).

Fig. 10. SEM micrographs of genital double-somites of females of Acartiella, ventral side. A, A. kempi; B, A. nicolae; C, A. sinensis. Scale bars: A, 20µm; B−C: 10µm. Abbreviations: gp, gonoporal plate; op, opercular pad.

Fig. 1. Distribution of the genus Acartiella based on the present and previous data. Three sampling sites in the present study in Thailand: Station 1, Prasae Estuary, Rayong Province, Gulf of Thailand (black triangle); Station 2, Bangpakong Estuary, Chon Buri Province, Gulf of Thailand (black circle); Station 3, Kraburi Estuary, Ranong Province, Andaman Sea (black square);. Previous distributional data: A. nicolae (Dussart 1985; Mulyadi 2004; Razouls et al. 2014); A. sinensis (Shen and Lee 1963; Zheng et al. 1982; Suwanrumpha 1987; Pholpunthin 1997; Orsi and Ohtsuka 1999; Pinkaew 2003; Shang et al. 2007; Razouls et al. 2014); A. kempi (Sewell 1914; Razouls et al. 2014); A. gravelyi (Sewell 1919; Razouls et al. 2014); A. keralensis (Wellershaus 1969; Razouls et al. 2014); A. major (Sewell 1932; Razouls et al. 2014); A. minor (Sewell 1919; Razouls et al. 2014); A. natalensis (Connell and Grindly 1974; Razouls et al. 2014); A. sewelli (Steur 1934; Razouls et al. 2014); A. tortaniformis (Sewell 1932; Razouls et al. 2014); and A. faoensis (Khalaf 1991; Ali et al. 2009; Peyghan et al. 2011; Razouls et al. 2014).

Fig. 2. Acartiella kempi Sewell, 1914, female. A, habitus, dorsal view; B, habitus, lateral view; C, right antennule; D, left antenna; E, left mandible; F, right maxillule; G, right maxilla. Roman numerals in C indicate numbers of ancestral segments following Huys and Boxshall (1991).