A new species of Pseudodiaptomus (Copepoda, Calanoida, Pseudodiaptomidae) from the Great Barrier Reef, Australia

69 A new species of Pseudodiaptomus (Copepoda, Calanoida, Pseudodiaptomidae) from the Great Barrier Reef, Australia Julian Uribe-Palomino1, T. Chad Walter2 1 CommonwealthScientificandIndustrialResearchOrganisation(CSIRO)Environment,QueenslandBiosciencesPrecinct,Brisbane,Australia 2 NationalMuseumofNaturalHistory,SmithsonianInstitution,Washington,DC,USA Correspondingauthor:JulianUribe-Palomino([email protected]) Copyright: © Julian Uribe-Palomino & T. Chad Walter. This is an open access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International – CC BY 4.0). Research Article Abstract A new species of the demersal calanoid copepod genus Pseudodiaptomus is described from specimens collected from the Great Barrier Reef, Australia. This species most closely resembles P. burckhardti in the structure of male fifth leg with reduced endopods on both legs, but differs from the latter in several features, including armatures of male fifth leg, asymmetrical female urosome and posterodorsal projections on the male prosome. Key words: Copepods, demersal, endemic species, South Pacific Ocean Introduction Copepods are highly diverse micro-crustaceans and are probably the most abundant of the metazoans in aquatic systems. Their habitats range from free-living planktonic, meiobenthic, demersal and even parasitic. The free-living copepods of the genus Pseudodiaptomus Herrick, 1884 currently, consists of 84 valid species (Walter and Boxshall 2025). Members of this genus are primarily demersal and typically found in shallow coastal estuarine-marine environments, extending from freshwater to hypersaline waters, and reside near or on the bottom during the day and migrate throughout the water column from dusk to dawn (Walter 1984, 1986, 1987). The mouthparts and swimming legs are very similar among the species, making these body parts of limited use for species determination even though, it is known some variability among the Pseudodiaptomus species (Walter 1986; Srinui et al. 2013; Mulyadi 2022; Nishida et al. 2024). However, the fifth pair of male swimming legs are highly dimorphic and have high taxonomic value, and occasionally in females the prosome and urosome augmentations are species specific. The separation of species in this genus is facilitated by using species groups and subgroups (Walter 1986), which were updated by Walter et al. (2002: 666). From the 84 accepted species of Pseudodiaptomus, it is known that 16 species of them inhabit coastal and surrounding waters from Australia, which has a vast territory in the Pacific, the Indian, and the Southern Oceans mainly, but also includes maritime and insular territory in tropical equatorial Academic editor: Kai Horst George Received: 12 March 2025 Accepted: 16 October 2025 Published: 21 November 2025 ZooBank: https://zoobank. org/8CFAA4CB-A30B-475B-B74E21B25367E437 Citation: Uribe-Palomino J, Walter TC (2025) A new species of Pseudodiaptomus (Copepoda, Calanoida, Pseudodiaptomidae) from the Great Barrier Reef, Australia. ZooKeys 1261: 69–81. https://doi. org/10.3897/zookeys.1261.152830 ZooKeys 1261: 69–81 (2025) DOI: 10.3897/zookeys.1261.152830 70 ZooKeys 1261: 69–81 (2025), DOI: 10.3897/zookeys.1261.152830 Julian Uribe-Palomino & T. Chad Walter: Pseudodiaptomus greenwoodi sp. nov. from the Great Barrier Reef waters. Those species and their primary location are mentioned as follow: P. annandalei Sewell (1919) [Queensland]; P. australiensis Walter (1987) [Northern Territory]; P. baylyi Walter (1984) [Northern Territory, Queensland]; P. clevei Scott A. (1909) [Aru Island, Papua New Guinea, Australia]; P. colefaxi Bayly (1966) [Queensland, New South Wales, Victoria]; P. cornutus Nicholls (1944) [Victoria, South Australia ]; P. galleti (Rose, 1957) [Western Australia, Shark Bay]; P. griggae Walter (1987) [Papua New Guinea, Aru Archipelago and Queensland]; P. hickmani Sewell (1912) [New South Wales, Cooks River]; P. hypersalinus Walter (1987) [Western Australia, Shark Bay], P. inflexus Walter (1987) [Queensland]; P. mertoni Früchtl (1923) [Aru Islands, Indonesia; Queensland, Port Curtis]; P. occidentalus Walter (1987) [Western Australia]; P. ornatus (Rose, 1957); P. pacificus Walter (1986) [Queensland]; P. serricaudatus (Scott T., 1894) [Queensland, Heron Island]. The new species described in this paper is based on material found in samples from the Great Barrier Reef that were donated by A.D. McKinnon and M.S. Talbot during 1978–1980. These collections have been housed at the Smithsonian Institution, National Museum of Natural History (NMNH) for the last 40 years and only recently studied and determined that they contained this new species. Materials and methods Specimens were fixed and preserved in 10% neutralized formalin/seawater after collection and then were transferred to 70% ethanol at the Smithsonian Institution, United States National Museum (USNM). Male and female specimens were stained with chlorazol black and transferred to depression slides in a solution of glycerine–ethanol for detailed examination under a Wild stereoscope. Habitus and dissected appendages were examined and illustrated with the aid of a camera lucida attached to a Nikon Optiphot DIC Phase Contrast Compound Microscope. Digitalization of the drawings was achieved by using Adobe Illustrator v. 27.9.6. Z-stacking images of the habitus of a pair of adult male and female specimens and their corresponding fifth legs were obtained using an Olympus DP80 digital camera attached to an automated upright epifluorescence microscope Olympus BX63 with CellSens operating software and a motorized Z-drive from the USNM. Body measurements of male and female specimens were made using a fluorescence microscope Olympus BX51 also at USNM. All measurements were done with a calibrated ocular micrometre and are presented in millimetres. Prosome length was measured from its most anterior margin to the posterior tip of the prosome and urosome length was measured from the anterior insertion on prosome to the posterior tip of caudal rami. Body and appendage terminology follows the terminology established by Huys and Boxshall (1991). Systematics Order Calanoida Sars, 1903 Family Pseudodiaptomidae Sars, 1902 Genus Pseudodiaptomus Herrick, 1884 71 ZooKeys 1261: 69–81 (2025), DOI: 10.3897/zookeys.1261.152830 Julian Uribe-Palomino & T. Chad Walter: Pseudodiaptomus greenwoodi sp. nov. from the Great Barrier Reef Pseudodiaptomus greenwoodi sp. nov. https://zoobank.org/D8C6AF0B-75AE-4C68-B35F-6B102D077413 Figs 1–5 Type locality. Australia, Queensland, Great Barrier Reef, Lizard Island, 14°40.45'S, 145°26.49'E, captured using light traps over coral reef. Type specimens. Holotype: ♂; USNM 1754446. Allotype: ♀; USNM 1754447. Paratypes: Australia • 10 ♀♀, • 10 ♂♂; Great Barrier Reef, Lizard Island; Jan.1978; M.S. Talbot; USNM 1754448; specimens intact; all types removed from original collection USNM 1110847. Additional material. Australia • 2 ♂♂, 2 ♀♀; Great Barrier Reef; Jul. 2000; A.D. McKinnon; USNM 310675 • 3 ♀♀; Queensland, Haughton River Estuary; Sep 1992; A.D. McKinnon; USNM 310761 • 100+ specimens; Queensland, Great Barrier Reef, coral reef, Lizard Island; Jan. 1977–Jan. 1978; M.S. Talbot; USNM 1110845–1110847; captured using light traps over reefs. Description. Common features shared by females and males: Antennule (Fig. 1A, B) of females and left male antennule possessing 22 segments, segments 6 and 7 partly fused and counted separately, with modified barbed seta on segment 20. Figure 1. Pseudodiaptomus greenwoodi sp. nov. A. Female antennule; B. Male antennule left; C. Male antennule right. 72 ZooKeys 1261: 69–81 (2025), DOI: 10.3897/zookeys.1261.152830 Julian Uribe-Palomino & T. Chad Walter: Pseudodiaptomus greenwoodi sp. nov. from the Great Barrier Reef Setal elements: (segment number = setae + aesthetasc [ae]) Female: 1 = 1 + ae, 2 = 2 + ae, 3 = 1 + ae, 4 = 2 + ae, 5 = 2 + ae, 6–7 = 2 + ae, 8 = 2 + ae, 9 = 1 + ae, 10 = 1 + ae, 11 = 1 + ae, 12 = 2 + ae, 13 = 1 + ae, 14 = 2 + ae, 15 = 2, 16 = 2, 17 = 2, 18 = 1, 19 = 2, 20 = 2 + ae, 21 = 2, 22 = 7. Male: 1 = 1 + ae, 2 = 1 + ae, 3 = 2 + ae, 4 = 1 + ae, 5 = 1 + ae, 6-7 = 2 + ae, 8 = 0 + ae, 9 = 1 + ae, 10 = 0 + ae, 11 = 1 + ae, 12 = 2 + ae, 13 = 2 + ae, 14 = 2 + ae, 15 = 2, 16 = 2, 17 = 1 + ae, 18 = 1, 19 = 1, 20 = 2 + ae, 21 = 2, 22 = 7. Figure 2. Pseudodiaptomus greenwoodi sp. nov., cephalic appendages. A. Antenna; B. Mandible; C. Maxillule; D. Maxilla; E. Maxilliped. 73 ZooKeys 1261: 69–81 (2025), DOI: 10.3897/zookeys.1261.152830 Julian Uribe-Palomino & T. Chad Walter: Pseudodiaptomus greenwoodi sp. nov. from the Great Barrier Reef Figure 3. Pseudodiaptomus greenwoodi sp. nov., male. A. Habitus dorsal view; B. Urosome enlarged view; C. Caudal rami dorsal view; D. Leg 5 posterior view; E. Leg 5 anterior view. Antenna (Fig. 2A): coxa without seta, basis and first endopodal segment completely fuse with 1 seta each, endopodal segment 2 with 8 and 8 setae on terminal and subterminal lobes respectively; exopod 3-segmented, first without seta, second with 1 proximal, 2 medial and 1 terminal setae; third with 3 medial and 4 terminal setae. 74 ZooKeys 1261: 69–81 (2025), DOI: 10.3897/zookeys.1261.152830 Julian Uribe-Palomino & T. Chad Walter: Pseudodiaptomus greenwoodi sp. nov. from the Great Barrier Reef Mandible (Fig. 2B): basis inner margin with 4 setae; endopod 2-segmented, first with 4 setae, second with 6 setae; exopod 5-segmented, first to fifth segments with 1, 1, 1, 1, 3 setae, respectively. Gnathobase with one long serrate dorsal seta and 3 cuspidate and 4 small, rounded teeth. Maxillule (Fig. 2C): praecoxal arthrite with 8 strong setae; coxa with 4 setae on endite and 9 on epipodite; basis with 4 and 5 setae on proximal and distal endites respectively; basal exite with 1 reduced seta; endopod 3-segmented, with 4, 2 and 6 setae respectively; exopod with 8 setae along margin. Maxilla (Fig. 2D): praecoxa, coxa and basis partially fused and, exopodite quite reduced without visible segmentation. Praecoxal endites with 3 and 3 setae respectively; coxal endites with 2 setae each; basal endite with 2 setae and endopod with 7 setae. Maxilliped (Fig. 2E): praecoxa and coxa completely fused, endites with 0, 2, 3, 4 setae; basis with 3 setae; endopod 6-segmented, with 1 seta on the first segment, second and third segments bearing 2 simple setae and 2 special robust mid-margin serrate setae; 1 seta on fourth and fifth segments and, 7 setae on sixth segment. Legs 1–4 (not figured, as they are alike in shape and armature to figures published by Walter (1986), Srinui et al. (2013), and Nishida et al. (2024)), symmetrical and biramous with 3-segmented rami; coxa and basis of both rami with spinules on distal corner. Seta and spine formula as follows: Male (Figs 3A–E, 5C, D). Body length 1.11–1.12 mm (n = 5); prosome length 2.4 times urosome. Cephalosome and first pedigerous somite separate and pedigerous somites 4 and 5 fused with distolateral acute projections. Urosome 5-segmented, symmetrical, segments 2–4 posterodorsal margins with rows of acute spinule rows extending laterally. Caudal rami symmetrical, each ramus with 1 lateral, 4 terminal and 1 dorsal setae. Urosomites and caudal rami with proportions 12:27:14:12:14:21 = 100. Male right antennule (Fig. 1C) 21-segmented, segments 6 and 7 separate, geniculate at segment 18-19. Setal elements: 1 = 1 + ae, 2 = 1, 3 = 1 + ae, 4 = 2 + ae, 5 = 1, 6 = 2 + ae, 7–8 = 3 + ae, 9 = 1 + 2ae, 10 = 0 + ae, 11 = 0 + ae, 12 = 1 + ae, 13 = 1 + ae, 14 = 2 + ae, 15 = 1 + ae, 16 = 2 + ae, 17 = 0, 18 = 1, 19 = 1 and medial spiniform projection, 20 = 2 + ae, 21 = 7. Leg 5 (Fig. 3D, E). Right leg: basis quadrate, with large plumose posterior-surface seta, anterior-surface sub-distal row of spinules, one small proximomedial knob-like process and a small digital medial endopod which is terminally pointed with short subterminal seta. Exopod 1 compressed, with distolateral large spiniform process, medial margin with large finger-like process terminally hirsute with fine spinules and terminal seta (visible in anterior view). Exopod 2 elongated and curved with a large distolateral spine reaching to midlength of exopod 3, medial margin with a groove lined with small spinules and a seta. Exopod 3 medially curved, tapering distally, medial margin with fine spinules and two proximal setae. Left leg: basis of similar size and shape to right leg basis with large coxa basis exopod endopod Leg 1 0-1 0-0 I-1; 0-1; II, 1, 3 0-1; 0-1; 1, 2, 3 Leg 2–3 0-1 0-0 I-1; I-1; II, 1, 5 0-1; 0-2; 2, 2, 4 Leg 4 0-1 1-0 I-1; I-1; II, 1, 5 0-1; 0-2; 2, 2, 3 75 ZooKeys 1261: 69–81 (2025), DOI: 10.3897/zookeys.1261.152830 Julian Uribe-Palomino & T. Chad Walter: Pseudodiaptomus greenwoodi sp. nov. from the Great Barrier Reef lateral seta at mid-length, anterior-surface sub-distal row of spinules, and small distomedial endopod with terminal seta. Exopod 1 small quadrate with a large distolateral spine. Exopod 2 oval with a very large proximolateral spine, a small sub-lateral seta at mid-length, surrounded by fine spinules, terminates in a pair of short stout spines, the terminal spine larger, and 3 medial setae. Figure 4. Pseudodiaptomus greenwoodi sp. nov., female. A. Habitus dorsal view; B. Urosome enlarged view; C. Urosome 1–3 ventral view; D. Leg 5 posterior view. 76 ZooKeys 1261: 69–81 (2025), DOI: 10.3897/zookeys.1261.152830 Julian Uribe-Palomino & T. Chad Walter: Pseudodiaptomus greenwoodi sp. nov. from the Great Barrier Reef Figure 5. Pseudodiaptomus greenwoodi sp. nov., female. A. Habitus dorsal view; B. Leg 5 posterior view; male, C. Habitus dorsal view; D. Leg 5 posterior view. 77 ZooKeys 1261: 69–81 (2025), DOI: 10.3897/zookeys.1261.152830 Julian Uribe-Palomino & T. Chad Walter: Pseudodiaptomus greenwoodi sp. nov. from the Great Barrier Reef Female (Figs 4A–D, 5A, B). Body length, 1.33–1.39 mm (n = 5). Prosome length 2.6 times urosome. Cephalosome and pedigerous somite 1 separate, pedigerous somites 4 and 5 completely fused with 2 symmetrical distally directed posterolateral spinelike projections and lined with fine spinules on each side of urosome insertion. Urosome 4-segmented, genital double-somite slightly asymmetrical, swollen at midlength and ventrally, darker towards the swollen genital aperture with double row of proximal spinules, distally the genital aperture is covered with a 3-lobed operculum, 2 lateral lobes thinner and expanded posteriorly, and a medial lobe triangulate tapering distally covering paired gonopores fused into a U-shaped structure. Urosomites 2 and 3 of similar size, lacking spinule rows on posterodorsal margins; somites 3 and 4 asymmetrical, right lateral margin reduced producing a curvature; somite 3 left posterolateral margin with small spinule patch. Caudal rami asymmetrical, right ramus mediolaterally curved and slightly thinner. Each ramus with typically 1 lateral, 4 terminal and a small dorsal setae. Medial margins of each ramus lined with fine setules. Urosomites 1–4 and caudal rami with proportions 34:12:12:13:29=100. The egg sac is single when present. Leg 5 uniramous and slightly asymmetrical; basis slightly swollen medially, with a large plumose lateral seta on posterior surface. Exopods 3-segmented, exopod 1 rectangular and 2 times longer than basipod, with distolateral spine. Exopod 2 distomedial corner produced and pointed with serrated hyaline process, left one slightly larger than the right, and short distolateral seta. Exopod 3 slender with serrate margins and a proximomedial spine. Endopods lacking. Etymology. The species is named in honour of Dr Jack Greenwood (University of Queensland), an Australian copepod taxonomist, who donated many Australian pseudodiaptomid samples over the years to the second author. Distribution. This species is currently known from the north of the Great Barrier Reef up to coastal waters of Townsville and surrounding areas. Discussion Morphological features of Pseudodiaptomus greenwoodi sp. nov. are unique among the Australian species with the female’s possession of paired posterior projections on pedigerous segments 5, and the male leg 5 left and right endopods are simple and much reduced in size. Based on the male leg 5 morphology, it is easy to assign this species to the Burckhardti species group of Walter (1986), as the leg 5 right and left endopods are rudimentary, small and simple, and exopod 1 has a small medial thumb shaped projection. The female and left male antennule have 22 segments and the 20th a barbed seta, and females have a single egg sac. The original description of P. burckhardti Sewell, 1932 was based only on females collected from the Nicobar and Andaman Islands, and later Pillai (1980) redescribed the species and presented the male of the species from the same locality. His redescription did not report the lateral spinule row on the female urosomite 3, though he noted that the female leg 5 exopodal segment 1 distolateral corners with spinule patch. Pillai’s figures were very small and not clear. Pseudodiaptomus burckhardti was redescribed again by Walter (1986) from samples collected from Palau Islands. Male pedigerous somite with paired dorsal lateral projections (Fig. 6A), female urosomite 3 possesses a spinule row only on right lateral margin and simple leg 5 and asymmetrical caudal rami