Acartia italica Steuer 1910

Acartia italica Steuer, 1910 Material examined Neotype During his working life at the “Zoologische Station der Berliner Aquariums” in Rovinj (Croatia), Steuer collected an impressive collection of planktonic material, including the type specimens of A. italica. Unfortunately, all was lost, especially during the world wars. An adult female 920 µm in length, was collected within samples from Lake Rogoznica in Central Adriatic Sea in Croatia, on April 13, 2000. Designated here as a neotype, this specimen is deposited at the Croatian Natural History Museum, Zagreb, No. HPM-BSZ, 1824. Additional material including individuals of all naupliar and postnaupliar stages from the same locality, collected in April 2000, was deposited at the Croatian Natural History Museum, Zagreb, No. HPM-BSZ, 1825. Results Redescription of the adults Adult female (Figure 7G) total length (excluding caudal setae): 880–960 µm (914.3 ± 27.9 µm, n=14). Nauplius eye present. Proportional lengths of female prosome somites: 46: 24: 10: 9: 11= 100. Prosome: urosome ratio including caudal rami = 2.9:1. Prosome 3.2 times longer than wide. Proportional lengths of urosomites and caudal rami 43: 19:19:19 = 100. Genital double-somite (Figures 11A, B) 1.05 times longer than wide; genital area symmetrical, located ventrally, with copulatory pores and seminal receptacles paired (Figures 9B, 11A). Rostrum powerfully developed, rounded frontally and triangular in ventral view; bearing two long, slender rostral filaments (Figures 8, 11C). The caudal rami are symmetrical and about 1.8 times longer than wide. Each ramus is armed with 1 lateral, 1 ventral and 4 distal setae (Figure 10I). The adult female antennules (Figure 13C) are symmetrical and reach almost to the end of the cephalosome. The adult segmentation and setation patterns are as follows: segment 1 (ancestral I–V) 1 seta; segment 2 (ancestral VI–IX) 7 setae + 2 ae; segment 3 (ancestral X) 1 seta + spine; segment 4 (ancestral XI–XII) 3 setae + ae; segment 5 (ancestral XIII) 1 seta; segment 6 (ancestral XIV–XV) 2 + ae; segment 7 (ancestral XVI) 1 seta + ae; segment 8 (ancestral XVII) 1 seta; segment 9 (ancestral XVIII) 1 + ae; segment 10 (ancestral XIX) 1 seta; segment 11 (ancestral XX) 1 seta; segment 12 (ancestral XXI) 1 setae + ae; segment 13 (ancestral XXII) 1 seta; segment 14 (ancestral XXIII) 1 seta; segment 15 (ancestral XXIV) 2 setae (1 anterior and 1 posterior); segment 16 (ancestral XXV) 2 setae + ae; segment 17 (ancestral XXVI) 2 setae; and segment 18 (ancestral XXVII–XXVIII) 4 setae + ae. The antenna (Figure 16F) is biramous, with endopod longer than exopod. The allobasis bears a total of 8 setae, plus the distal seta; the elongate middle endopodal segment bears a total of 7 setae located distally on the inner margin; the apical segment is slightly more elongate, with 7 plumose setae around apex. Two rows of spinules are present on the allobasis curving across the segment and onto the outer margin. The exopod is about as long as the allobasis and is 4-segmented, with the first segment elongate; the segmental setation pattern is 1, 2, 2, 3. The mandible (Figure 17F) comprises a large coxa, which forms the gnathobase medially, plus a biramous mandibular palp. The cutting edge of the gnathobase is produced into 8–9 heterogeneous teeth. The proximal part representing the basis is longer than wide and armed with a single seta located distally on the margin. The basis carries single inner seta. The endopod is 2-segmented, with the first segment bearing 2 short setae and the second 9 setae. The exopod appears indistinctly 5-segmented and is armed with 1,1,1,1,2 setae. The maxillule (Figure 18F) is a multilobate limb. It bears the praecoxal endite, the coxal endite and the basal endite along the inner margin; the apical lobe represents the exopod, and the outer margin carries the basal exite distally and an array of setae proximally which represent the incorporated epipodite. The praecoxal arthrite bears 9 elements, the coxal epipodite is represented by 9 setae. The maxilla (Figure 19F) is uniramous, but with traces of incomplete segmentation appearing in the adult. It is armed with a total of 19 setae: the setal formula for the praecoxal and coxal endites is 4, 2, 2, 3 setae; the basis carries 2 setae; the endopod is indistinctly 3-segmented, with a setal formula of 2, 2, 2 (Figure 19F). The maxilliped (Figure 20F) is 4-segmented. The proximal segment (syncoxa) carries 6 spinulate setae (Figure 20F). The basis is oval in shape and bears 1 seta proximally on the inner margin. The endopod is 2-segmented and the distal segment carries 2 unequal apical setae; the proximal segment is armed with 3 spiniform setae. The segmentation and the armature of the swimming legs 1–4 are presented in Figures 21F, 22F and 23E, 24E. The legs are biramous. In all legs the coxa is unarmed. The armature formula is as follows: Leg 5 in females is symmetrical, uniramous and 3-segmented (Figure 25C). The coxae and intercoxal sclerite are fused to form a broad, unarmed coxal plate. The basis is elongate, and the spinous process is about twice as long as the basis. The distal segment represents the exopod, which forms a claw-like spinous process distally arising from a bulbous base. It is ornamented with setules distally on both margins (Figure 25C). Male (Figure 7I) total length: 755–860 µm (813 ± 41.7 µm, n=16). Prosome 2.9 times longer than wide. Cephalosome and pedigerous somites similar to those of adult female. Rostral area as in female. Prosome: urosome ratio = 2.7: 1. Proportional lengths of urosomites plus caudal rami: 14:28:22:4:16:16 = 100. Genital somite symmetrical, wider than long, not expanded ventrally (Figure 10K, L). The left antennule of the adult male (Figure 15A) is 21-segmented and has the following setation pattern; segment 1 (ancestral I–V) 1 seta; segment 2 (ancestral VI–VII) 3 setae + 1 ae; segment 3 (ancestral VIII–IX) 4 setae + ae; segment 4 (ancestral X) 1 seta + spine; segment 5 (ancestral XI) 2 setae + ae; segment 6 (ancestral XII) 1; segment 7 (ancestral XIII) 1; segment 8 (ancestral XIV) 1 seta + spine + ae; segment 9 (ancestral XV) 1 seta; segment 10 (ancestral XVI) 1 seta + ae; segment 11 (XVII) 1 seta; segment 12 (ancestral XVIII) 1 seta + ae; segment 13 (ancestral XIX) 1 seta; segment 14 (ancestral XX) 1 seta; segment 15 (ancestral XXI) 1 seta + ae; segment 16 (ancestral XXII) 1 seta; segment 17 (ancestral XXIII) 1 seta; segment 18 (ancestral XXIV) 2 setae (1 anterior and 1 posterior); segment 19 (ancestral XXV) 2 setae + ae; segment 20 (ancestral XXVI) 2 setae; segment 21 (ancestral XXVII–XXVIII) 4 setae + ae. The right antennule of the adult male (Figure 15B) is 18-segmented, with the neocopepodan geniculation located between segments 13 (ancestral segment XX) and 14 (representing a secondarily fused triple segment derived from ancestral segments XXI–XXIII. The other secondary fusion in the right antennule is segment 4 which now represents ancestral segments X and XI, which were separate at the preceding stage and are separate in the left antennule. The expressed segmentation and setation patterns are as follows; segment 1 (ancestral I–V) 1 seta; segment 2 (ancestral VI–VII) 3 setae + ae; segment 3 (ancestral VIII–IX) 4 setae + ae; segment 4 (ancestral X–XI) 3 setae + spine + ae; segment 5 (ancestral XII) 1 seta; segment 6 (ancestral XIII) 1; segment 7 (ancestral XIV) 2 setae + spine + ae; segment 8 (ancestral XV) 1 seta; segment 9 (ancestral XVI) 1 seta + ae; segment 10 (XVII) 1 seta; segment11 (ancestral XVIII) 1 seta + ae; segment 12 (ancestral XIX) 2 setae; segment 13 (ancestral XX) 1 seta; segment 14 (ancestral XXI–XXIII) 1 seta + 2 spines + ae; segment 15 (ancestral XXIV) 2 setae (1 anterior and 1 posterior); segment 16 (ancestral XXV) 2 setae + ae; segment 17 (ancestral XXVI) 2 setae; segment 18 (ancestral XXVII–XXVIII) 4 setae + ae. The antenna, mouthparts and swimming legs 1–4 are identical to those of female. The male fifth legs are uniramous and asymmetrical (Figure 25F). The coxae and intercoxal sclerite are fused to form a broad, unarmed coxal plate. The basis is armed with a seta on the outer distal margin. The basis of the right fifth leg is expanded into an inner lobe. The first exopodal segment is elongate and armed with a naked seta located medially; the second segment is markedly expanded medially and carries a short spine distally on the inner expansion; the third segment is curved inwards and armed with a short apical spine and a small seta on the concave inner margin (Figure 25F). The first exopodal segment of the left leg is longer than wide, but unarmed; the distal segment is armed with a robust apical spine and is produced subdistally into 3 small digitiform lobes, the longest of which is ornamented with short setules. Description of the developmental stages Egg and spermatophore The diameter of the subitaneus eggs was 67 to 82 µm (74.1 ± 2.9 µm, n=50). The outer surface of subitaneus eggs was coated with branched spines, spaced out so they are separated from each other by approximately 2 µm. Scanning electron micrographs were taken of the eggs by Kršinić et al. (2000). The flask of the spermatophore is 110 µm long and has a diameter of 20 µm; the proximal 20 µm of the extended neck has a diameter of 0.7 µm; the distal part is dichotomously forked and forms two attachment discs (Figures 11A, D). Naupliar stages The bodies of all naupliar stages are presented in Figure 2. The body length of the naupliar stages increases linearly from 110 µm (NI) to 260 µm (NVI) (Figure 3). The frontal margin of all stages is rounded with a shallow swelling in the middle. The posterior part varies from stage to stage in its surface spinular ornamentation, in the presence of the post-mandibular limbs, and in the state of the developing limb buds. The labrum occupies a large proportion of the ventral surface of NI stage and lacks any surface ornamentation. The relative size of th