Tortanus (Atortus) minicoyensis, Francis & Nandanb, 2019

Francis, Sanu Vengasseril & Nandanb, Sivasankaran Bijoy, 2019, A new species of Tortanus (Atortus) (Copepoda, Calanoida, Tortanidae) from Minicoy Island, southeastern Arabian Sea, Turkish Journal of Zoology 43 (5), pp. 425-436 : 427-433

publication ID	https://doi.org/ 10.3906/zoo-1811-29
persistent identifier	https://treatment.plazi.org/id/1142FC51-FFF5-9943-FFBD-256EFD59F8F4
treatment provided by	Felipe
scientific name	Tortanus (Atortus) minicoyensis
status	sp. nov.

Treatment

Tortanus (Atortus) minicoyensis View in CoL sp. nov. ( Figures 2–5 View Figure 2 View Figure 3 View Figure 4 View Figure 5 ) 3.1. Type

Holotype: Adult female, dissected parts were preserved in a small vial in 4% formaldehyde/seawater with a drop of glycerol ( ZSI-C6655 /2) . Allotype: Adult male ( ZSI-C6656 /2) . Paratypes: 5 females ZSI-C6657 ; 1 dissected and 4 intact males ZSI-C6658 /2.

Fifteen intact females ( MBM /DBT/10/15) and 15 intact males ( MBM /DBT/09/15) preserved in a vial were deposited as nontype materials.

3.2. Description

Female: Total length, 2.66–2.94 mm (mean ± SD = 2.80 ± 0.07 mm, N = 20; holotype, 2.82 mm); prosome length 2.1–2.29 mm (2.19 ± 0.09 mm; holotype, 2.23 mm), width 0.82–0.97 mm (0.89 ± 0.07 mm; holotype, 0.83 mm). Prosome ( Figure 2A View Figure 2 ) about 3.5 times as long as urosome. Cephalosome and first pedigerous somite separated; fourth and fifth somite fused. Fifth pediger asymmetrical: left margin with a notch, right margin with a single downward

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directed triangular lobe. Urosome composed of 2 segments; genital compound somite asymmetrical; right margin with a prominent bulge at about midpoint ( Figure 2C View Figure 2 ) with 2 ventrolateral pointed spines ( Figure 2D View Figure 2 ). Genital operculum semicircular, ventrally located at anterior onethird of the genital compound somite. Second urosomite (anal somite) completely fused with caudal rami. Caudal rami asymmetrical, with 2 rounded processes. Left ramus slightly broader than right ramus ( Figures 2A, 2C View Figure 2 ). All specimens carrying hyaline coupling device with left process larger than the right one, covering the dorsolateral process of fifth pedigerous somite and left lateral surface of

genital compound somite ( Figures 2A, 2C, 2D View Figure 2 ). Antennule ( Figure 2B View Figure 2 ) 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. Armatures as follows: I–IX, 9 + 2ae (aesthetascs); X, 2; X–XIV, 7 + ae; XV, 1; XVI, 1 + ae; XVII, 0; XVIII, 2 + ae; XIX, ae; XX, 2; XXI, ae; XXII, 1; XXIII, 1; XXIV, 1; XXV, 1 + 1 + ae; XXVI–XXVIII, 6 + ae. Antenna ( Figure 3A View Figure 3 ) coxa unarmed; basis and first endopodal segment completely fused with medial seta at proximal third, distomedial seta and distolateral row of spinules, second and distal segments incompletely fused,

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distal segment with proximolateral setules and 6 apical setae. Exopod 3-segmented, proximal segment short, naked; middle and distal segment incompletely fused with 3 and 2 setae, respectively. Mandible blade ( Figure 3C View Figure 3 ) with 5 cuspidate teeth, main tooth and second ventral-most tooth separated by wide diastema; both teeth with articulated tip; dorsal-most tooth monocuspidate while remaining 2 teeth bicuspidate, 4 dorsal-most teeth with 4 longitudinal spinule rows proximally; mandibular palp ( Figure 3B View Figure 3 ) basis elongate, cylindrical and unarmed; endopod 2-segmented, proximal segment unarmed, distal segment with 6 setae. Exopod 1-segmented, with 5 setae. Maxillule ( Figure 3D View Figure 3 ) basis absent, precoxal arthrite with 11 spinulose setae apically and 2 setae dorsally; coxal endite with 3 stout, spinulose terminal setae. Maxilla ( Figure 3E View Figure 3 ) syncoxal endites with 1, 2, 2, and 3 setae from proximal to distal; basal endite with 1 developed and 2 rudimentary setae; endopod with 5 stout setae with claw-like tip and 2 rudimentary setae. Maxilliped ( Figure 3F View Figure 3 ) syncoxa with 2 endites, each with spinulose seta; basis unarmed; endopod with 3 medial spinulose setae and lateral seta. Legs 1–4 with 2-segmented endopods and 3-segmented exopods ( Figures 4A–4D View Figure 4 ). Distal endopodal segment of legs 1–4 with hair tuft on anterior surface subdistally. Seta and spine formula as in Table 1. Outer setae on leg 1 basis minute. Leg 5 uniramous ( Figure 3G View Figure 3 ), 2-segmented, symmetrical with coxa, and intercoxal sclerite fused as a basal plate; exopodal lobe trapezoid with distolateral seta bearing fine hairs along its margin.

Male: Total length, 2.25–2.74 mm (mean ± SD = 2.35 ± 0.05 mm, N = 20; allotype, 2.27 mm), prosome length 1.62–1.73 mm (1.73 ± 0.05 mm; allotype, 1.72 mm), width 0.59–0.67 mm (0.65 ± 0.07 mm; allotype, 0.62 mm). Prosome about 3 times as long as urosome ( Figure 5A View Figure 5 ). Posterior corners of pedigerous somite 5 symmetrical, rounded. Urosome of 5-somites. Second urosomite with posterolateral and posteroventral processes on right side ( Figure 5D View Figure 5 ), of which latter smaller, each with minute setae on the tip. Caudal rami are nearly symmetrical. Cephalic appendages similar to those of female except right antennule. Right antennule geniculate ( Figure 5B View Figure 5 ), 16-segmented; ancestral segment I–VIII (segment 1), XXI–XXIII (segment 15), and XXIV–XXVIII (segment 16) totally or partially fused; segments XVI–XIX expanded. Armature as follows: I–VIII, 11 + 2ae; IX, 2; X, 2; XI, 2 + ae; XII, 1; XIII, 1; XIV, 2; XV, 1; XVI, 2 + ae; XVII, 2; XVIII, 2 + ae, XIX, 1 + P (process); XX, 1 + P; XXI–XXIII, 2 + ae + 2P; XXIV–XXVIII, 9 + 2ae. The anterior surface of segment XX furnished with a serrated ridge that retroflexes near base of segment XX and extends to the triangular process of segment XIX ( Figures 5B, 5C View Figure 5 ). Hinge joint formed between segment XX and fused segments XXI–XXIII. The distal end of the segment with a long spinous process extending the half-length of the fused segments XXIV–XXVIII. Legs 1–4 as in female. Right leg 5 coxa semitrapezoid ( Figure 5E View Figure 5 ) with the beak-like medial process; basis semicircular with seta on posterior surface and digitiform medial process bearing 2 setae, one distal and the other basal ( Figure 5E View Figure 5 ). Exopod 1-segmented, slightly curved medially, tapering distally into the narrow tip, bearing 1 minute seta on midanterior. Left leg 5 ( Figure 5F View Figure 5 ) longer than the right, coxa without seta. Basis elongate, straight, with 3 low, rounded processes at regular intervals and lateral seta at distal third and medial seta halfway along the inner margin of the segment. Exopod 2-segmented, the proximal segment with proximomedial, digitiform process bearing subdistal seta, distal segment with patches of setules on the anterior surface, 2 lateral minute setae, 2 medial setae, and blunt subdistal seta strongly curved along the hemispherical tip of the segment with the granular surface ( Figure 5G View Figure 5 ).

Etymology: The specific name minicoyensis refers to the name of the type locality of this species. It therefore is a toponymic term, agreeing in gender with the masculine generic name.

3.3. Molecular analysis

The mtCOI sequences were successfully generated using the primer pair, reaction mix, and thermal regime described above. The developed sequences of female and male T. minicoyensis sp. nov. were submitted to the NCBI database and assigned the following accession numbers: KP749951 to KP749953 for males, and KP749954 for females. ML analysis was performed, and pairwise sequence distances were generated and analyzed using the developed sequences as well as the mtCOI sequences of their 9 congeneric species acquired from the NCBI database ( Table 2). Nassodonta insignis H. Adams, 1867 ( KP 739843) was selected as the outgroup. The ML tree clearly exhibited the differential assemblage of congeneric species of the genus Tortanus (Figure 6). Female and male T. minicoyensis sp. nov. sequences were arrayed within a single clade with a high bootstrap value (100%), which is distinct from all other sequences of subgenus Atortus based on 1000 bootstrap pseudo-replicas. The outgroup N. insignis exhibited maximum divergence array. The level of inter- and intraspecific divergence persisting within the genus Tortanus was evident from the distance matrix data. Specifically, T. minicoyensis sp. nov. possessed an intraspecific sequence divergence ranging from 0%–0.4% ( Table 3).

3.4. Remarks

The subgenus Atortus has been classified into 2 morphological groups; the first one is the tropicus group sensu Othman, 1987, and the second is the murrayi group sensu Othman, 1987 ( Ohtsuka and Kimoto, 1989; Mulyadi et al., 2017). From the structure of female leg 5, male antennule, and leg 5, Tortanus (A.) minicoyensis sp. nov. is assigned to the tropicus species complex within the subgenus Atortus Ohtsuka, 1992 . The female of T. minicoyensis sp. nov. can be distinguished from all other species of the tropicus group ( T. bowmani Othman ,

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1987; T. digitalis Ohtsuka & Kimoto, 1989 ; T. giesbrechti Johns & Park, 1968 ; T. longipes Brodsky, 1948 ; T. rubidus Tanaka, 1965 ; T. ryukyuensis Ohtsuka & Kimoto 1989 ; T. taiwanicus Chen & Hwang, 1999 ; T. tropicus Sewell, 1932 ; T. vietnamicus Nishida & Cho, 2005 ; T. andamanensis ; T. sigmoides Nishida, Anandavelu & Padmavati, 2015 ) by the following: (1) the asymmetrical fifth pedigerous somite with notched left margin and triangular lobe on the right, (2) hyaline coupling device with larger left process covering the dorsolateral process of fifth pedigerous somite and left lateral surface of genital compound somite, (3) two ventrolateral spines in the genital compound somite, and (4) asymmetrical caudal rami with two medial rounded processes in the female. The male is distinguished from all the other species of the tropicus group by (1) serrated ridge of the right antennule produced proximally over onethird of segment XIX and the ridge slightly raised from the surface plane of the segment, (2) beak-shaped medial process on the right fifth leg coxa, (3) triangular medial process with a depression on the distomedial margin on the basis, and (4) strongly curved subdistal seta on the left fifth leg.

The species of the subgenus Atortus hitherto known from the Indian Ocean are Tortanus (Atortus) andamanensis and T. sigmoides Nishida, Anandavelu & Padmavati, 2015 ; T. magnonyx Ohtsuka & Conway, 2005 ; T. insularis Ohtsuka & Conway, 2003 ; T. nishidai Ohtsuka, El Sherbiny & Ueda, 2000 ; T. tropicus Sewell, 1932 ; and T. recticauda Giesbrecht, 1889 (http:// copepodes.obs-banyuls.fr/en). Among them, T. tropicus is the largest (female 2.71 mm; male 2.29 mm) ( Sewell, 1932). However, the new species herein described has the largest length range known in the genus (female 2.66– 2.94 and male 2.25–2.74 mm). The differential diagnosis of T. minicoyensis sp. nov. with all other species of the subgenus Atortus from the Indian Ocean is represented in Tables 4 and 5. T . minicoyensis sp. nov. was found swarming along with Acartia bispinosa Carl, 1907 , Labidocera madurae A. Scott, 1909 , Undinula vulgaris Dana, 1849 , and Centropages orsinii Giesbrecht, 1889 in the present collection. The swarming behavior of members of the subgenus Atortus have been observed in oligotrophic clear waters mainly in subtropical and tropical areas (Kimoto et al., 1988; Ohtsuka and Kimoto, 1989; Ohtsuka and Reid, 1998; Ohtsuka et al., 2000) as a response to the presence of prey copepods, and also to avoid visual predators ( Ohtsuka et al., 2000). The mtCOI sequences were developed for T. minicoyensis sp. nov. to bring out the molecular variance from the congeners and establish the female–male correspondence of the species. The speciation of T. minicoyensis sp. nov. is exhibited in the genetic distance matrix, which showed an intraspecific divergence of 0%–0.4%, which is under the threshold value of 4% for calanoid copepods ( Bucklin et al., 2010).