Diacyclops leijsi Karanovic 2024, sp. nov.

Diacyclops leijsi sp. nov. (Figs. 1A, 2–7) urn:lsid:zoobank.org:act: 0268C544-772E-431D-B2D1-CD78AE4862DD Type locality. South Australia, Wabma Kadarbu Mound Springs, sample no. TC17049, 29.453111°S 136.858°E, 15 March 2003, collected by R. Leijs. Holotype. Adult female dissected on one microscope slide. Paratypes. One male and 1 female from type locality dissected on 1 microscope slide each; 2 males and 3 females from type locality on 1 SEM stub (row no. 6), together with 5 other species described here; 4 males, 7 females, and 2 copepodids from type locality in 1 alcohol vial. Etymology. The species is named after Dr. Remko Leijs, South Australian Museum, Adelaide, who collected this species and entrusted it to me for identification. The name is a noun in the genitive singular. Diagnosis. Female. Body length, excluding caudal setae, from 440 to 485 µm. Habitus (Figs. 1A, 6A) spindle-shaped, nearly 2.8 times as long as wide, with prosome/urosome ratio of 1.25, and posterior end of cephalothorax about 2.5 times as wide as genital double-somite in dorsal view. Integument on all somites thin and wrinkled, with dense bacterial cover, spinules only on anal somite and caudal rami, cuticular pores on all somites, and sensilla on all but penultimate somite. Hyaline fringes of prosomites smooth, while those of genital double-somite and 2 subsequent urosomites coarsely serrated (Figs. 1A, 6B). Genital double-somite (Fig. 2A) slightly wider than long in ventral view, widest at first fifth of its length and gradually tapering posteriorly, widest part about 1.5 times as wide as posterior margin; seminal receptacle large and shaped like a mature mushroom; copulatory pore relatively large; copulatory duct short, narrow, and well-sclerotized. Anal somite (Fig. 2A) with small spinules along ventral margin. Caudal rami (Fig. 2A) slender, narrowly spaced, nearly 5 times as long as wide and 3 times as long as anal somite; principal terminal setae without breaking planes, inner one about 1.2 times as long as entire urosome and 1.6 times as long as outer one; dorsal seta about as long as caudal ramus, 1.5 times as long as innermost terminal seta, and twice as long as outermost terminal seta. Antennula (Figs. 2B, 6E) 17-segmented, slightly longer than cephalothorax, with single aesthetasc on twelfth segment and setae formula 8.4.2.6.3.2.2.1.1.0.1.1.0.1.2.2.8; ultimate segment about 2.4 times as long as wide. Antenna (Fig. 3A) 5-segmented, without exopodal seta, with setae formula 0.2.1.8.7; second and fifth segment of similar length. Labrum (Fig. 3B) trapezoidal, with 2 diagonal rows of 10 slender spinules each on anterior surface; cutting edge nearly straight, with 14 sharp teeth between pointed lateral corners. Mandibula (Fig. 3C, D) slender, with 2 long and 1 short seta on 1-segmented palp; cutting edge with 4 slender spinules on anterior surface, 8 apical teeth, and dorsalmost unipinnate seta; ventralmost tooth strongest and quadricuspidate, second, fourth, and seventh teeth from ventral side bicuspidate, all other teeth unicuspidate. Maxillula (Figs. 3E, 6C) composed of praecoxa and 2-segmented palp, unornamented; praecoxal arthrite bearing 4 strong distal spines and 6 medial elements; palp with slender exopodal seta, 3 slender setae on endopod, and 1 strong and 2 slender setae on inner margin of coxobasis. Maxilla (Figs. 3G, 6C) 4-segmented, with 2 slender setae on praecoxa, 1 slender seta on proximal endite of coxa, 1 strong and 1 slender seta on highly mobile distal endite of coxa, basis expanded into robust claw with 1 strong and 1 very slender seta, and endopod with 3 strong and 2 slender setae. Maxilliped (Figs. 3H, 6C) 4-segmented, with long spinules on second and third segment and setae formula 3.2.1.3. All swimming legs (Figs. 4A, B, C, D, E, 6D) large and wide, with smooth intercoxal sclerite with slightly concave distal margin, each leg composed of minute and triangular praecoxa, large and rectangular coxa, short basis, 3-segmented exopod and 3-segmented endopod; basis of first leg with long outer seta and long inner spine, latter slightly longer that first 2 endopodal segments combined; basis of second to fourth legs with shorter outer seta and inner distal corner pointed; all first and second exopodal segments, all first endopodal segments, and second endopodal segment of first and second legs with single inner seta; second endopodal segment of third and fourth legs with 2 inner setae; third exopodal segments spine formula 2.3.3.3 and setae formula 4.4.4.4; third endopodal segments of first to third leg with 3 inner setae, 1 apical seta, 1 apical spine, and 1 outer seta; third endopodal segment of fourth leg nearly twice as long as wide, with 2 inner setae, 2 apical spines, and 1 outer seta; its outer spine nearly 1.3 times as long as segment or inner spine. Fifth leg (Figs. 2A, 4F) small and slender, 2-segmented, with single outer seta on first segment and apical seta and subapical inner spine on second segment; second segment about 2.2 times as long as wide and only slightly longer than its spine. Sixth leg (Fig. 4G) small semicircular plate, with long seta and 2 minute spines; seta almost as long as plate width. Male. Body length from 435 to 465 µm. Habitus (Fig. 6F) and urosome (Fig. 5A) slightly slenderer than in female; free genital somite (Figs. 5A, 7D) more than 1.5 times as wide as subsequent urosomite, with relatively small ovoid spermatophores. Ornamentation of cephalothorax (Fig. 6F), free prosomites (Figs. 6F, 7C), and urosomites (Fig. 7D, E, F) as in female. Caudal rami (Figs. 5A, 6F) slightly slenderer than in female, with slightly shorter dorsal and innermost terminal setae. Antennula (Figs. 5B, 7A, B) slender, strongly prehensile and digeniculate, 16-segmented, with anvil-shaped cuticular ridges on anterior margin of fourteenth and fifteenth segments (distal geniculation); 3 aesthetascs present on first segment, while fourth, ninth, and thirteenth segments carry 1 aesthetasc each; setae formula 8.4.2.2.2.2.1.1.2.2.2.2.1.2.1.13; several setae minute and slender, 1 on each ninth, eleventh, and twelfth segment spiniform, and 2 pairs of setae on ultimate segment fused basally; penultimate segment about 2.5 times as long as wide. Antenna, labrum, mandibula, maxillula, maxilla, maxilliped, all swimming legs (Fig. 5C), and fifth leg (Fig. 5A) as in female. Sixth leg (Fig. 5A, D) longer than in female, with better developed innermost spine and with central slender seta; outermost seta about 2.7 times as long as spine or central seta.