Bioacoustics of Heterolaophonte discophora

Remarks. Heterolaophonte discophora ( Willey, 1929 ) was originally described by Willey (1929) based on a female specimen collected from St. Andrews, New Brunswick , Canada . The male was subsequently reported from Passamaquoddy Bay, New Brunswick , by Willey (1931) . However, these initial descriptions and illustrations were brief and provided limited morphological details, particularly regarding the P 5 of both sexes and the P 2 – P 4. Lang (1965) later provide a detailed redescription based on specimens collected from Monterey Bay, near Hopkins Marine Station, and treated H. rotundipes Chappuis, 1958 , (originally described from Puget Sound near Seattle, Washington , USA ) as a junior synonym of H. discophora . Following Lang’s taxonomic revision, Itô (1974) also redescribed the species based on male and female specimens from Hokkaido , Japan . Given the incompleteness of the original description, the present comparison of the Korean material relies primarily on the comprehensive accounts by Lang (1965) and Itô (1974) . Heterolaophonte discophora was first reported from Korea in the doctoral dissertation by Song (2000) . In that study, Song identified specimens collected from macroalgae at Masan-ri, Pohang, as H. discophora , providing a brief species description, with the setal formula of P 2 – P 4 and illustrations of the female P 1 , P 4, P 5, the A 2 exopod, the caudal ramus, and the male P 5. He noticed that the Korean H. discophora machted Itô’s (1974) redescription in all characters except for the relative lengths of the two short inner setae on the male P 5. We obtained Korean specimens of H. discophora from MPD stranded along the coasts of Gohado, Mokpo, and Naechi Beach, Sinan, as well as Masan-ri. Contrary to Song’s (2000) observations, our examination of these newly collected Korean specimens reveals additional morphological differences not previously reported. One of the diagnostic traits of H. discophora is the shape of the P 4 exp - 3, which is slender and elongated, gradually broadening distally in its proximal part ( Willey 1929 : fig. 2; Lang 1965 : fig. 264 a). However, this characteristic appears less pronounced in Japanese specimens ( Itô 1974 : fig. 264 a, a. 1) and in the Korean material examined here (Fig. 8 D ). Nonetheless, the markedly large and broad P 4 exp - 1 in H. discophora , relative to exp - 2 and exp - 3, may represent a more reliable diagnostic feature of this species than the morphology of exp - 3 when compared to congeners. Comparative analysis of the Korean specimens with previous records of H. discophora reveals four distinct morphological traits. Lang (1965) reported four setae on the endopodal lobe of the female P 5, whereas Chappuis (1958) and Itô (1974) described five; the Korean specimens also possess five setae on this lobe. It is possible that Lang (1965) observed a variable condition of the female P 5, considering that most Heterolaophonte species have five setae on the corresponding segment, except for H. exigua (Scott, 1912) , H. norvegica Drzycimski, 1968 , and H. tupitskyi Chislenko, 1976 . In the male P 5, Lang (1965) and Willey (1931) described five elements, whereas Chappuis (1958) and Itô (1974) noticed seven elements, including two additional small inner setulae — features also observed in the Korean material. It appears that these two inner ornamentations were interpreted as armatures by earlier authors. Regarding the female P 3 endopod, Itô (1974) reported three inner setae on the enp - 2; however, most Korean specimens only have two, with occasional asymmetry (bearing 2 or 3 inner setae) between the left and right rami (see variability above). Lang (1965) described the male P 3 endopod as three-segmented, and Itô (1974) referred to a tripartite condition, though with indistinct boundaries. Conversely, the Korean specimens consistently exhibit a two-segmented endopod, although a posterior suture line is variably developed — absent in some individuals, faint in others, and distinctly visible in a few — potentially leading to interpretative ambiguity. Similar variable chaetotaxy has occasionally been reported in laophontid copepods, particularly in the genus Quinquelaophonte , which is closely related to Heterolaophonte ( Willen 1996 ; Kim and Lee 2023 ). Finally, Itô (1974) noted a single triangular, spur-shaped protuberance on the outer distal corner of the male P 3 enp - 2, which, unfortunately, was not mentioned by Lang (1965) . In contrast, the Korean specimens exhibit two triangular, strengthened spinules (protuberances?) of unequal size in the same position, with a similar row of strong spinules also present proximally along the outer margin. This ornamentation was probably overlooked by earlier authors. In addition, the Korean specimens exhibit several minor differences from previous accounts. They have three setae on the endopod of the maxilla, whereas Lang (1965) described two, and Itô (1974) reported only one. In the female P 5 exopod of the Korean material, only three of the five setae are bare, whereas all were described as bare in previous accounts. In the male P 4 exopod, the terminal segment is similar in length to the second segment, but it is slightly longer in Lang’s (1965) and Itô’s (1974) material. In the male P 2 enp - 2, the apical outer seta is longer than the inner distal seta, whereas the reverse condition was described previously. Except for the first difference, these minor disparities are considered herein as intraspecific variability.