Tortanus (Atortus) dhritiae Francis and Jasmine, 2022

Bijoy Nandan, Sanu V. Francis P. Jasmine S., 2022, A new species of Tortanus (Atortus) Ohtsuka, 1992 (Copepoda, Calanoida, Tortanidae) from Great Nicobar Island, north-eastern Indian Ocean, Nauplius (e 2022021) 30, pp. 1-9 : 2-4

Tortanus (Atortus) dhritiae Francis and Jasmine sp. nov.

( Figs. 2–4 )

Zoobank: http://zoobank.org/ urn:lsid:zoobank.org:act:DEA28079-A9EA-4373-8266-BEA553171E73

Type material. Holotype: adult female (TL: 2.28 mm) dissected parts were mounted on a glass slide ( ZSI-C9205 /2) . Allotype: 1 adult male (TL: 1.96 mm) dissected and mounted on a glass slide ( ZSI-C9210 /2) . Paratypes: 1 undissected female ZSI-C9206 /2 (TL: 2.26 mm) and 1 undissected male ZSI-C9207 /2 (TL: 1.87 mm) .

Other material examined. 1 undissected female (MBM/16/21) and 1 undissected male (MBM/17/21) preserved in a vial were deposited as non-type material.

Type locality. India, Great Nicobar Island , off

Lakshman beach, 07°01’25.2”N 93°55’ 23.0”E.

Description. Female.Total body length: 2.21–2.28 mm (mean ± SD = 2.25 ± 0.04 mm, N = 3); prosome length: 1.79–1.81mm (1.8 ± 0.01 mm, holotype: 1.81 mm); width: 0.65–0.7 mm (0.68 ± 0.03 mm, holotype: 0.7 mm).Prosome ( Fig. 2A ) about 3.8 times long as urosome; cephalasome and first pedigerous somite separated; left joining side of fourth and fifth pedigerous somite with notch. Fifth pediger asymmetrical; left margin rounded, right margin with single downward directed triangular lobe. Urosome composed of 2 segments, genital compound somite symmetrical. Genital operculum semi-circular, ventrally located at anterior part of genital compound somite. Second urosomite (anal somite) completely fused with caudal rami. Caudal rami asymmetrical, left ramus broader than right. Anterior portion of left ramus produced into rounded process to the right. All specimens carry hyaline coupling device. Left process produced from notch between fourth and fifth pedigerous somites, covering left ventrolateral surface of fifth pedigerous somite and left lateral surface of genital compound somite. Right process produced from dorsolateral surface of genital compound somite, covering lateral surface of genital compound somite and reaching up to three-fourths of right caudal ramus. Antennule ( Fig. 2C, D ) 15 segmented, symmetrical, reaching posterior margin of caudal ramus. Ancestral segments I–IX (segment 1), XI–XIV (segment 3), and XXVI–XXVIII (segment 15) totally or partially fused. Armature as follows; I–IX, 6 (setae) + ae (aesthetascs); X, 3; XI–XIV, 5+ae; XV, 0; XVI, 1+ae; XVII, 0; XVIII, 2; XIX, 0; XX, 2; XXI, ae; XXII, 1; XXIII, 1; XXIV, 0+1; XXV, 1+1; XXVI–XXVIII, 6+ae. Antenna ( Fig. 2E ) coxa unarmed, basis and first endopodal segment incompletely fused with medial seta at proximal third, distomedial seta and distolateral row of spinules, second and distal segments incompletely fused, distal segment with proximolateral setules and 6 apical setae. Exopod 2-segmented, proximal segment short and naked, distal segment with distomedial seta and 4 apical setae. Mandible palp ( Fig. 2F ) basis elongate, cylindrical and unarmed; endopod 2-segmented, proximal segment unarmed, distal segment with 6 setae. Exopod 1 non-segmented with 5 setae. Mandible gnathobase ( Fig. 2G ) with 5 cuspidate teeth, main tooth and second ventralmost tooth separated by wide diastema; both tips with articulation; dorsal-most tooth monocuspidate while remaining 2 teeth bicuspidate, 4 dorsal-most teeth with 4 longitudinal spinule rows proximally. Maxillule ( Fig. 2H ) basis absent, precoxal arthrite with 11 spinulose setae apically and 2 small setae; coxal endite with 3 stout, spinulose terminal setae. Maxilla ( Fig. 2I ) syncoxal endite with 1, 2, 2 and 3 setae from proximal to distal; basal endite with 6 stout setae with claw-like tip and 2 rudimentary setae. Maxilliped ( Fig. 2J ) syncoxa with 2 endites, each with a spinulose seta; basis unarmed; endopod with 3 medial spinulose setae and lateral seta. Legs 1–4 with 2-segmented endopods and 3-segmented exopods ( Fig. 3A–D ). Distal endopodal segment of legs 1–4 with setal tuft on anterior surface subdistally. Seta and spine formula as in Tab. 1. Outer setae on leg 1 basis minute. Leg 5 uniramous ( Fig. 2K ), 2-segmented, symmetrical with coxa, and intercoxal sclerite fused as a basal plate; exopodal lobe elliptical shaped with distolateral seta bearing fine setules along its margin.

Male. Total length: 1.87–1.96 mm (mean ± SD = 1.92 ± 0.05 mm, N= 3); prosome length: 1.38–1.51 mm (1.45 mm, allotype: 1.46 mm); width 0.49–0.52 mm (0.5 ± 0.02 mm, allotype: 0.52 mm). Prosome 3 times as long as urosome ( Fig. 4A ). Posterior corners of the pedigerous somite 5 symmetrical, rounded. Urosome composed of 5 somites. Second urosomite with posterolateral and posteroventral process on right side ( Fig. 4E ), one of which smaller, each with minute setae on tip. Caudal rami nearly symmetrical. Cephalic appendages similar to those of female except right antennule. Right antennule geniculate ( Fig. 4B ), 16-segmented; ancestral segment I–VII (segment 1), XXI–XXIII (segment 15), and XXIV–XXVIII (segment 16) totally or partially fused; segments XVI–XIX expanded. Armature as follows: I–VII, 7+2ae; VIII, 2; IX, 2; X, 2; XII, 1-ae; XIII, 0; XIV, 2; XV, 0, XVI, 2+ae; XVII, 1; XXVIII, 2+ae; XIX, 1+1P (process); XX, 1+1P; XXI–XXIII, 2+ae+2P; XXIV–XXVIII, 1+7+ae.Theanteriorone-thirdsurface of segment XX furnished with serrated ridge that retro-flexes near base of segment XX, extending to triangular process of segment XIX ( Fig. 4 B–D ).Hinge joint formed between segment XX and fused segments XXI–XXIII. Legs 1–4 as in female. Right leg 5 coxa obtuse trapezoid ( Fig.4F ) with triangle-shaped medial process; basis semi-circular with a slight curve near base and crocodilian head-shaped medial process with small process distally and bearing 2 setae, one distal and one medial.Exopod non-segmented, slightly curved medially, with medial seta and blunt tip bearing 1 minute seta on outer margin and 1 seta on inner margin. Left leg 5 ( Fig. 4G ) longer than right, coxa unarmed. Basis elongate, straight with lateral seta at distal third and medial seta halfway along inner margin of segment. Exopod 2-segmented, proximal segment with proximomedial, digitiform process bearing subdistal seta, distal segment with patches of setules on anterior surface, 2 lateral minute setae, 2 medial setae, and blunt subdistal seta slightly curved along hemispherical tip of segment with granular surface.

Etymology. The species is named in honor of Dr. Dhriti Banerjee, the first woman director of the Zoological Survey of India, one of the leading organizations involved in taxonomic studies of Indian fauna. This species is also dedicated to all women researchers in the field of taxonomy.

Remarks. The subgenus T. (Atortus) has been divided into the tropicus- group sensu Othman, 1987, and the murrayi -group sensu Othman, 1987 ( Ohtsuka and Kimoto, 1989; Mulyadi et al., 2017). Ohtsuka and Kimoto (1989) have further subdivided the tropicus -group into longipes- and rubidus- groups (plus one unassigned group), and the murrayi- group into murrayi- and recticauda -groups, and renamed the tropicus and murrayi species groups as brevipes and recticauda species complexes, respectively ( Ohtsuka and Kimoto, 1989; Mulyadi et al., 2017). Nishida and Cho (2005), Nishida et al. (2015), Francis and Bijoy Nandan (2019) (as in the present study) retain the group name tropicus proposed by Othman (1987) since the male of Tortanus (Atortus) brevipes A. Scott, 1909 has not yet been described. Tortanus (A.) dhritiae sp. nov. is assigned to the tropicus species complex and closely resembles Tortanus (Atortus) minicoyensis Francis and Bijoy Nandan, 2019 . The female of T. (A.) dhritiae sp. nov. can be distinguished from all other species of the tropicus - group[ T. (Atortus) brevipes ; Tortanus (Atortus) tropicus Sewell, 1932 ; Tortanus (Atortus) longipes Brodsky, 1950 ; Tortanus (Atortus) rubidus Tanaka, 1965 ; Tortanus (Atortus) giesbrechti Jones and Park, 1968 ; Tortanus (Atortus) bowmani Othman, 1987 ; Tortanus (Atortus) ryukyuensis Ohtsuka and Kimoto, 1989 ; Tortanus (Atortus) digitalis Ohtsuka and Kimoto, 1989 ; Tortanus (Atortus) taiwanicus Chen and Hwang, 1999 ; Tortanus (Atortus) vietnamicus Nishida and Cho, 2005 ; Tortanus (Atortus) andamanensis Nishida, Anandavelu and Padmavati, 2015 , Tortanus (Atortus) sigmoides Nishida, Anandavelu and Padmavati, 2015 ; Tortanus (Atortus) indonesiansis , Tortanus (Atortus) omorii Mulyadi, Nishida and Ohtsuka, 2017 , Tortanus (Atortus) processus Mulyadi, Nishida and Ohtsuka, 2017 , Tortanus (Atortus) lukmani Mulyadi, Nishida and Ohtsuka, 2017 , and T. (Atortus) minicoyensis Francis and Bijoy Nandan, 2019 ] by the following characteristics: (1) left lateral joining of fourth and fifth pedigerous somite with a notch;(2) asymmetrical caudal rami, left ramus broader than right; anterior portion of the left ramus produced with a rounded process to the right ramus; (3) leg 5 exopodal lobe elliptical shaped with distolateral curved seta. The male is distinguished from all other species of the tropicus -group by (1) the serrated ridge on the anterior one-third surface of segment XX of the right antennule, (2) obtuse trapezoid-shaped right leg 5 coxa with triangle-shaped medial process, (3) semi-circular basis with a slight curve near base and crocodilian head-shaped medial process with small process distally and bearing one distal and one medial seta.

Figures

Figure 2.Tortanus (Atortus)dhritiae sp.nov.,female (holotype):A)habitus dorsalview;coupling device is dotted; B)urosome ventral view; C, D) antennule; E) antenna; F) mandible palp; G) mandible gnathobase; H) maxillule; I) maxilla; J) maxilliped; K) leg 5.

Figure 3.Tortanus (Atortus) dhritiae sp. nov., female (holotype), legs 1–4, anterior view: A) leg 1; B) leg 2; C) leg 3; D) leg 4.

Figure 4. Tortanus (Atortus) dhritiae sp. nov. male (allotype): A) habitus dorsal view; B, C, D) antennule; E) urosome second segment right lateral view; F) right leg 5 posterior view; G) left leg posterior view.