A new species of Parategastes Sars , 1904 from the Thale Noi Lake , southern Thailand ( Copepoda , Harpacticoida , Tegastidae )

Parategastes pholpunthini sp. n. is described and illustrated based on material collected in the Thale Noi Lake, Phatthalung province, southern Thailand. This species can be distinguished from its congeners by the number segments of female antennule, the lengths of rami and basis of P1, the shape of middle inner seta of P4 exp-3, shape of P5, and relative lengths of spine at apically of baseoendopod of P5. The differences among Parategastes species are pointed out and they are compared with the new species. An identification key to species of the genus Parategastes are proposed.


Introduction
The family Tegastidae Sars, 1904 is characterised as being laterally compressed, amphipod-like, strongly chitinous and well sculptured (Huys et al. 1996).To date, this family comprises approximately 60 species in six genera.Each genus can be easily distinguished by the number of segments in P2-P4 and the length of caudal ramus (Gollner et al. 2008).This family is widely distributed, and has been recorded in areas such as the Andaman Islands, India (Fiers 1986); southwestern Australia (Bartsch 1995); the Mid-Atlantic Ridge (Ivanenko and Defaye 2004); Spitsbergen in the Arctic Ocean (Ferrari et al. 2007); a hydrothermal vent site on the East Pacific Rise (Gollner et al. 2008); the Gulf of Mexico (Plum and Arbizu 2009); and a hydrothermal vent in the Okinawa Trough, Japan (Back et al. 2010).One of the six genera, Parategastes, was created by Sars (1904) who proposed this genus base on the number segments of female antennule (6-7 segments), maxilliped and shape of P5.In addition, Parategastes sphaericus was proposed Type species.Parategastes sphaericus (Claus, 1863).
Generic diagnosis.Parategastes Sars, 1904.antennules with 6-7 segments in female and 8 segments in males; exopod of antenna with one segment and with two or three setae; anterior maxilliped with the 2 proximal lateral lobes replaced by simple setae, outermost lobe less broad and provided with only two setae at the tip, terminal joint produced at the tip to a long digitiform process.P2 and P3 with 2-segmented endopod and 3-segmented exopod; and P4 with 3-segmented endopod and exopod, whilst enp-1 was not swollen.P5 in female, baseoendopod very large, with inner expansion to broad and vaulted, exopod somewhat dilated towards the end, with a single short apical seta.
Additional materials.8 females and 8 males from the type locality are stored in 70% ethanol.
Description of the adult female.Body laterally compressed with sensilla, surface of whole body pitted (Fig. 1A).Total length, measured from the anterior margin of the cephalic shield to the posterior margin of the caudal rami, 280-340 µm (mean = 310 µm, n = 11).Prosome comprising of cephalothorax and three somites bearing P2 to P4. Urosome 5-segmented (Fig. 1D), first urosomite with P5, genital double somite and three abdominal somites.Caudal rami (Fig. 1C) as wide as long, with seven setae of different lengths.All setae smooth.
Egg sac (Fig. 2G) round, containing four eggs, located ventrally between fifth pair of legs.
Mandible (Fig. 2C) gnathobase with four teeth.Coxa-basis with row of long spinules and with two setae; endopod 1-segment with three setae; exopod represented by one seta.
Maxilla (Fig. 2E) syncoxa with transverse row of spinules proximo-laterally and with two endites.Precoxal endite with four setae, one seta elongated; coxal endite with three setae.Allobasis with three setae, middle seta forming a strong claw, and three setae at outer margin representing endopod.
Maxilliped (Fig. 2F) subchelate, 2-segmented, comprising syncoxa and basis.Syncoxa with one pinnate seta at the inner distal corner.Basis with row of spinules, one pad-like process ornamented with short spinules on its surface.Endopod 1-segmented, forming a strong claw with one seta proximally.P1 (Fig. 3A) coxa with a row of setules along inner margin.Basis with a row of spinules along inner margin, one inner seta, and one outer seta.Both rami with 1-segmented endopod wider than exopod.Endopod with a row of setules along outer margin; with one inner proximal biplumose seta, one inner middle modified spine, one inner distal bipinnate spine, two apical bipinnate spines, and one outer bipinnate spine.Exopod with a row of spinules along inner margin; with two apical bipinnate spines, three outer setae, the middle of which being bare, and the others bipinnate.
P2 and P3 (Figs 3B, 4A) coxa with a set of spinules on pronounced disto-lateral corner.Basis elongated with one small outer seta and row of spinules along medial margin.Rami with 3-segmented endopods and 2-segmented exopods; all segments of endopod with a row of setules     along outer margins, all segments of exopod with a row of spinules along outer margin.
P4 (Fig. 4B) coxa with a set of spinules on pronounced disto-lateral corner.Basis elongated with one small outer seta and a row of spinules on the inner and outer margins.Both rami 3-segmented.Enp-1 and enp-2 equal in length but shorter than enp-3; enp-1 and enp-2 with inner setae and with a row of setules along outer margins; enp-3 with two apical pinnate spines, and one outer seta.Exp-1 small, with one outer spine; exp-2 with one inner seta and one outer spine, and with a row of spinules on the inner and outer margins; exp-3 with a row of spinules on the outer margin, with one inner pinnate seta, middle inner seta enlarged, this enlarged seta has a peculiar shape with two long pinnae at the distal third, with the bending, and with three shorter pinnae distal end, two apical setae, one seta plumose, another seta inner margin plumose and outer margin pinnate, and two outer pinnate spines.
Armature formula of P1-P4 as in Table 1.P5 (Fig. 4C) with baseoendopod and exopod; baseoendopod with three lateral biplumose setae, and one inner seta along proximolateral, apically with one inner bipinnate seta and one outer biplumose spine.Exopod with one apical biplumose seta and two outer bipinnate setae, one small seta basally.
Etymology.This species named after Dr. Pornsilp Pholpunthin, who has studied the freshwater copepods in Southern Thailand since last twenty years.

Discussion
Four Parategastes species have been recorded in the Oriental region (Sewell 1924, Thompson and Scott 1903, Humes 1984, Wellershaus 1970).They comprises of Parategastes sphaericus, P. chalmersi, P. conexus and P. caprinus.However, this is the first record of the genus Parategastes in Thailand.
Parategastes pholpunthini sp.n. is clearly distinguished from other Parategastes species in the following characters: (1) number of antennule segments of female, 7-segmented in most species of Parategastes, except P. coetzeei and P. pholpunthini sp.n. with 6-segmented; (2) P1, length of rami and basis in this genus can be separated into three groups: the first group, rami shorter than basis, comprises of P. chalmersi and P. conexus, the second group, rami approximately as long as basis, comprises of P. herteli and P. sphaericus and the third group, rami longer than basis, comprises of P. caprinus, P. coetzeei and P. pholpunthini sp.n. (Table 2).However, in the latter group, inner middle spine of P1 modified except P. caprinus; (3) P4, middle inner seta of exp-3 enlarged in various forms, in P. sphaericus and P. caprinus, this seta thickened and elongated with serrated margin at the middle to the distal end (see fig. 2 Jakobi 1953), P. pholpunthini sp.n., this seta has a peculiar shape with two long pinnae at the distal third, with the bending, and with three shorter pinnae distal end, and slender seta in P. coetzeei and (4) P5, baseoendopod, only P. conexus with sub-triangular shape, other species with sub-oval shape; all species in this genus, apically with inner seta as long as outer spine, except P. pholpunthini sp.n. length of inner seta twice of outer spine, and P. conexus length of inner seta twice of outer seta.
At present, the taxonomic status of members of the genus Parategastes is still unclear.Original descriptions and illustrations of type specimens of some species are poor.It seems that this genus is in need molecular data of each species.Note: not include P. haphe.-= no data; P1, lengths of rami relative to lengths of basis; l = exopod or endopod longer than basis; m = exopod or endopod approximately as long as basis; s = exopod or endopod shorter than basis; P4 exp-3, number and type of setae on inner edge; 3:wd:A = 3 setae, distal seta well developed, about as long as both proximal setae; 3:wd:B = 3 setae, distal seta well developed, about as long as the proximal seta but much shorter than the middle seta; 3:rud = 3 setae, distal seta very thin and weak, barely reaching to the end of the segment; 2 = setation of inner edge apparently represented by only the two very long proximal setae; P5, lengths of inner spine(seta) relative to lengths of outer spine(seta); A= inner seta as long as outer seta, B* = inner seta is twice of outer seta, B** = inner seta is twice of outer spine.

Table 2 .
Comparison of characters of female of Parategastes species (modified from Wells 2007).