Bioacoustics of Sagum lativentris

Remarks: Pillai (1985) reported a species under the name of “ Lernanthropus lativentris ” from Lethrinus harak (Forsskål, 1775) (as L. rhodopterus ) and Lutjanus vitta in Indian waters. Kabata (2005) concluded that the material identified and described by Pillai (1985) as L. lativentris in his monograph was misidentified, and he established L. pillaii Kabata, 2005 as a new species to accommodate Pillai’s material. We follow Kabata in recognizing that Heller’s L. lativentris is valid and distinct, but this species remained poorly known. It is unfortunate that Heller’s type material was not ovigerous, since the morphology of the egg sacs indicates that this species belongs in Sagum . The discovery of ovigerous material from the type host Lutjanus vitta (as Mesoprion phaiotaeniatus ) collected in Ambon , Indonesia revealed the nature of the loosely coiled egg sacs, so this discovery was reported by Pattipeiluhu & Gill (1998) under the combination Sagum lativentris , although the new combination status was not made explicit. There are another two very similar species currently placed in Lernanthropus , L. caesionis Yamaguti, 1954 and L. sanguineus Song, in Song & Chen, 1976 , which also appear to belong in Sagum . The former species was described by Yamaguti (1954) based on two females taken from the gills of Caesio cuning (Bloch, 1791) (as C . kuning ) caught off Sulawesi , Indonesia . A complete description of this species is not available but in addition to the habitus of the female, the unarmed endopod of leg 1 and the leaf-like shape of the caudal rami are typical of a cluster of Sagum species (see Table 4 ). We here transfer L. caesionis to Sagum as S. caesionis ( Yamaguti, 1954 ) n. comb. We note that S. caesionis is very similar to S. gurukun Uyeno & Naruse, 2018 , but can be distinguished by the length of the rami of leg 4. Finally, L. sanguineus was based on study of two females collected from Lutjanus sanguineus (Cuvier, 1828) caught at Sanya, Hainan Dao, China ( Song & Chen, 1976 ). The females were not ovigerous but the only subsequent record of this copepod was under the name Sagum sanguineus ( Song, 1976 ) and came from Vietnamese waters. This report was based on females from Lutjanus johnii ( Kazachenko et al ., 2014 ) and the name used was not explicitly identified as constituting a new combination, but the transfer to Sagum is confirmed below. After these generic transfers, Sagum now comprises 18 species ( Table 4 ). These three newly transferred species were not included in the comparisons made by Uyeno & Naruse (2018) when they established two new species of Sagum from the Ryukyu Islands, Japan , nor were they considered in the brief discussion in Kazachenko et al . (2017) who established S. vietnamensis Kazachenko, Kovalev, Nguyen & Ngo, 2017 . The key to species of the genus provided by Uyeno & Naruse (2018) needs to be updated, but here we provide a Table comparing key character states of all species. The material of S. lativentris collected from Lutjanus johnii in Australian waters has smooth linear lateral margins of the cephalothorax and tapering fourth legs, the tips of which may just extend beyond the posterior margin of the dorsal trunk plate when straightened. There are nine species that share these two character states ( Table 4 ). These same species all have a leaf-like caudal ramus, with the exception of S. vietnamensis which has cylindrical caudal rami that are about 4.4 times longer than wide according to Kazachenko et al . (2017) . Sagum lativentris has caudal rami that are about 2.8 times longer than wide and can be readily separated from S. caesionis and S. gurukun , which have short caudal rami (only 1.4 to 1.5 times longer than wide). The setation on the caudal ramus also provides useful characters: in S. bitaro Uyeno & Naruse, 2018 , S. folium , and S. paracaesionis Izawa, 2014 , the 2 dorsal caudal setae are located in the distal half of the ramus, whereas in S. lativentris these 2 setae originate in the proximal half. Sagum lativentris differs from S. foliaceum in body proportions: so the cephalothorax and anterior trunk combined are longer than the dorsal trunk plate in S. lativentris but markedly shorter in S. foliaceum . In addition the lobes of leg 4 extend well beyond the posterior margin of the dorsal trunk plate in the latter, but only the tips are visible in dorsal view in the former. Finally, S. lativentris and S. sanguineus are very similar morphologically and both use lutjanids as hosts. Indeed, both parasites have been recorded from the same host, L. johnii (present account; Kazachenko et al. 2014 ). The best characters to differentiate between them relate to the fourth legs and caudal rami. In S. lativentris the fourth legs have somewhat flaccid tips and are often bent, but when straightened the tips are visible beyond the posterior margin of the dorsal trunk plate, whereas in S. sanguineus the fourth leg lobes are more linear and the distal third of each is visible in dorsal view. The caudal rami in both species are about 2.7 to 2.8 times longer than wide but in S. lativentris the distal of the two dorsal setae is located at about 44% of the ramus length while in S. sanguineus it is located at about 30% of the ramus length. In addition, the tips of the caudal rami reach beyond the mid-length of the fourth leg lobes in S. lativentris ( Fig. 45B ) but do not reach the mid-length in S. sanguineus ( Fig. 47C ).