Lobothorax bharat, Mohapatra & Roy & Seth & Tripathy & Mohapatra, 2025

Lobothorax bharat sp. nov.

urn:lsid:zoobank.org:act:7F5091B7-3376-4182-9CB1-FF8B190DE374

( Figs. 1 View FIGURE 1 and 2 View FIGURE 2 )

Holotype. 1 ovig. female, 29.09 mm TL, 9.60 mm TW, Gopalpur fish landing centre , 8 May 2023, from Trichiurus lepturus Linnaeus, 1758 , coll. S. K. Mohapatra ( EBRC / ZSI / Cr-15704 ).

Paratypes. 1 male, 11.90 mm TL, 3.41 mm TW, Gopalpur fish landing centre , 8 May 2023, from same host fish, coll. S. K. Mohapatra ( EBRC / ZSI / Cr-15705 ); 4 non-ovig. females, 15.43–24.22 mm TL, 5.86–9.46 mm TW, Bahabalpur fish landing centre , Chandipur, 31 March 2023, from Trichiurus lepturus Linnaeus, 1758 , S. Roy and J. K. Seth ( EBRC / ZSI / Cr-15706 A–D ) .

Comparative materials examined. Lobothorax typus Bleeker, 1857 ; 1 ovig. female (23 mm), Nagappatinam, 30 May 2016, from Trichiurus lepturus Linnaeus, 1758 , coll. S. Ravichandran ( ZSI / MBRC D1-537); 8 females (15.9–22.5 mm), Gopalpur fish landing centre, 25 December 2018, from Trichiurus lepturus Linnaeus, 1758 , coll. S. R. Mohanty and J. K. Seth ( EBRC / ZSI /Cr-11090 & Cr-11091).

Diagnosis. Cephalon anterior margin sub-truncate; anterolateral process of pereonite 1 do not extend beyond anterior margin of cephalon; a distinct depression in the middle of pereonite 1; maxilliped palp article 3 with three recurved robust setae; the presence of a prominent mid-dorsal longitudinal ridge on the surface of both pereon and pleon.

Description of ovigerous female. Body elongated, length 3.03 times greatest width; dorsal surface smooth. Cephalon sub-truncate, 1.42 times as long as wide; apex smoothly rounded ( Fig. 3A View FIGURE 3 ). The eyes visible, prominent. Antennula 1.41 times of antenna length, with 8 articles; first 3 articles bulbous, larger than other articles in size, 0.20, 0.23 and 0.21 times respectively of the total antennula length while articles 5–8 gradually decreasing in size; article 4 corresponds to 0.06 of the total antennula length; article 5 to 0.09, article 6 to 0.07, the seventh to 0.06, and the eighth to 0.04 times respectively. Antenna composed of 9 articles; articles 1 and 2 are 0.12 and 0.11 times of overall antenna length, while articles 3 and 5 are larger in size, article 4 is the longest, 0.13 times of overall length. Articles 6 9 progressively decreasing in length; article 6: 0.10, article 7: 0.06, article 8: 0.06, and article 9: 0.03 times the overall antenna length. article 10 with a terminal seta on the tip. Both the antennula and antenna reach the anterior margin of pereonite 1. Mouthparts robust. Mandibular palp articles increase in size from articles 1–3. Maxilla with 2 large and 2 small terminal recurved setae. Maxillula with 4 robust setae. Maxilliped with 3 recurved robust setae on article 3 ( Fig. 3D–G View FIGURE 3 ).

Mid-dorsal ridge present on all pereonites, starting from half the length of pereonite 1. Pereonite 1 with distinct anteromedial depression, preceded by the dorsal ridge. Anterolateral process of pereonite 1 do not extend beyond anterior margin of cephalon; length 0.45 times the cephalon length. Pereonite 5 widest. Pleonite 1 largely concealed by pereonite 7 with only middle portion visible dorsally.

In pereopod 1, propodus length is 1.6 times; carpus length is 1.2 times; merus length is 0.2 times; ischium length is 1.6 times; basis length is 1.4 times of their greatest width. In pereopod 2, propodus length is 1.6 times; carpus length is 1.6 times; merus length is 0.2 times; ischium length is 1.9 times; basis length is 1.3 times of their greatest width. In pereopod 3, propodus length is 1.4 times; carpus length is 0.7 times; merus length is 0.3 times; ischium length is 1.3 times; basis length is 1.5 times of their greatest width. In pereopod 4, propodus length is 1.1 times; carpus length is 0.2 times; merus length is 0.5 times; ischium length is 1.5 times; basis length is 1.3 times of their greatest width. In pereopod 5, propodus length is 0.9 times; carpus length is 0.2 times; merus length is 0.3 times; ischium length is 1.7 times; basis length is 1.3 times of their greatest width. In pereopod 6, propodus length is 1.3 times; carpus length is 0.2 times; merus length is 0.4 times; ischium length is 1.9 times; basis length is 1.1 times of their greatest width. In pereopod 7, propodus length is 1.02 times; carpus length is 0.2 times; merus length is 0.5 times; ischium length is 2.3 times; basis length is 1.1 times of their greatest width. The length of pereopod 5–7 increases gradually. The length of pereopods is in order of 3<1<2<4<5<6<7. The size of the basis of the pereopods increases from 4 to 7. The coxae of pereopods 2 and 3 are not visible from dorsal view but the rest of the pereopod’s coxae are visible. The size of the coxae decreases from 2 nd to 7 th pereopod ( Fig. 4 View FIGURE 4 ). All pleopodal exopods are almost rounded as compared to their respective endopods, which are oval. All pleopodal peduncles are with developed lateral lobes. In pleopod 1, the length of the exopod is 1.5 times its greatest width and the length of the endopod is 1.2 times its greatest width. In pleopod 2 the length of the exopod is 1.03 times its greatest width and the length of the endopod is 0.9 times its greatest width. In pleopod 3 the length of the exopod is 1.2 times its greatest width and the length of the endopod is 0.9 times its greatest width. In pleopod 4 the length of the exopod is 1.4 times its greatest width and the length of the endopod is 1.01 times its greatest width. In pleopod 5 the length of the exopod is 1.1 times its greatest width and the length of the endopod is 0.9 times its greatest width. Four pairs of oostegites that emerge from sternites 2, 3, 4, and 6 form the brood pouch ( Fig. 3H View FIGURE 3 ). Each marsupium has nearly 170 spherical eggs.

Pleotelson sub-rectangular in shape, 0.4–0.5 times as long its wide; with caudomedial point. Uropods do not extend beyond the posterior margin of pleotelson; exopod length 0.9 times of endopod ( Fig. 3I View FIGURE 3 ), lateral margin of exopod with notch; apices of exopod and endopod acute.

Description of male. Body 3.49 times as long as wide. Mid-dorsal ridge is not developed. Cephalon sub-truncated. The anterior half of the cephalon is less wide compared to the posterior half. Antennula is smaller than the antenna. Each antennula has 8 articles and reaches the base of the origin of anterolateral expansion of pereonite 1, first 3 articles are wider and larger as compared to the last five articles. Antenna comprises 11 articles. The eyes are visible prominently and are 0.54 times the cephalon length.

Pereonite 3 and 4 widest and pereonite 7 is the narrowest. Lateral sides of pereonite 6and 7are curved posteriorly. All the coxae are visible dorsally. The chromatophores are distributed faintly on the mid-dorsal part of cephalon, pereonites and pleonite. All the pleonites are sub-equal in width. Pleonite 5 is longer than the other pleonites.

Pleotelson is sub-triangular in shape and 1.9 times wider than its length. Anterior part of the pleotelson is covered with numerous chromatophores. Uropod reaches the posterior margin of the pleotelson. The uropodal exopod length is a little longer than the endopod. The morphological measurements of the holotype and paratypes are represented in Table 2 View TABLE 2 .

Colour. Body creamy white when fresh. Yellowish-brown or dark brown when kept in ethanol. Caudomedial point of the pleotelson is brown.

Host. Trichiurus lepturus Linnaeus 1758 ( Trichiuridae ). The isopod attaches to the tongue of the host species, Trichiurus lepturus .

Distribution. The new species is known only from the coastal waters of Odisha coast, India.

Etymology. The species epithet Hindi word for India, which is ‘Bharat’.

Genetics. Lobothorax bharat sp. nov. differs genetically from one of the available sequences of the congener, i.e., L. typus with the K2P distance of 2.5–2.6% (having a base pair difference of 16–17). The new species differs from the other species of the buccal and branchial parasites used in the analysis by 23.9–32.2% K2P distance ( Table 3 View TABLE 3 ). In ML tree analysis, the new species appears in a different cluster from its congeners, L. typus , with strong bootstrap support of 100% ( Fig. 5 View FIGURE 5 ). The above finding is also supported by ASAP. In the ASAP analysis there is the formation of 10 partitions and the partition with the lowest ASAP scores indicates that the new species form a distinct group ( Fig. 6 View FIGURE 6 ).

Remarks. Lobothorax bharat sp. nov., is best identified by the following characters: Cephalon anterior margin sub-truncate; anterolateral processes of pereonite 1 do not extend beyond anterior margin of cephalon; a distinct depression in the middle of pereonite 1; maxilliped palp article 3 with three recurved robust setae; the presence of a prominent mid-dorsal longitudinal ridge on the surface of both pereon and pleon. In large specimens the endopod has distinct notch.

A comparison of different morphological features of the new species Lobothorax bharat sp. nov. and the other described species of the genus Lobothorax has been provided in Table 4 View TABLE 4 by following Richardson (1910); Yu & Bruce (2006); Aneesh et al. (2021).

Statistics. A total of 738 samples of Trichiurus lepturus host fish species were examined with 12 hosting Lobothorax bharat sp. nov. A prevalence rate of 1.62% and 1.09 intensity were observed.