Acartia italica Steuer 1910
Creators: name: Kršinić, Frano
name: Boxshall, Geoff A.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Copepoda
Calanoida
Acartiidae
Acartia
Acartia italica

description: 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 the labrum decreases proportionally through the nauplius phase and the free posterior margin is fringed with spinules from NII to NVI. The caudal armature comprises a single pair of setae at NI; a second pair is added at the moult to NIII, and from NIV to NVI there are 3 pairs of setae in total. The posterior part of the body carries a surface ornamentation of 2 rows of spinules in all naupliar stages. The antennules, antennae and mandibles are present in all naupliar stages. The first post-mandibular limb to appear is the maxillule which appears as a small lobe armed with 3 setae at NIV. The rudiment of the maxilla appears at NV, and at NVI the rudiments of the first and second legs are present.
The antennule is 3-segmented in all naupliar stages (Figure 4). The proximal segment is unarmed throughout the nauplius phase. The second segment bears 2 distally-located setae plus a setal rudiment is present proximally in NI to NIII. By NIV there are 4 setal rudiments present proximally on this segment. The distal segment carries 3 well developed setae at N I. New setae are added at each moult: so, NII has 4 setae, NIII has 7 setae, NIV has 8 naked setae, NV has 9 setae, all of which are plumose, and NVI has 12 plumose setae (Figures 4A–F).
The antenna is biramous and the protopodal part comprises separate coxa and basis. At NI the coxa is armed with a single naked seta while the basis carries 2 naked setae. From NII to NVI both coxa and basis are each armed with 1 strongly spinulate spine and 1 naked seta (Figure 5A–F). The endopod is unsegmented and armed with 4 setae in NI and NII; the number of setae increases to 6 in NIII and then to 7 setae in stages NIV to NVI. The exopod is 5-segmented, and armed in NI 6 setae, NII with 7 setae (Figure 5B) increasing to 8 setae in NIII–NVI (Figure 5C–F).
The mandible is biramous (Figure 6). The coxa is distinct at all stages and is armed with a single naked seta on its medial margin at NI, but with 1 spinulate seta in stages NII–NVI. The basis and exopod are fused; the basis carries 2 naked setae on the medial margin at stage NI, but has 2 spinulate setae in stages NII–NVI. The elongate exopodal lobe carries 4 defined segments distally, armed with a total of 5 plumose setae in NI to NIII. At the moult to NIV a naked seta is added proximally bringing the total to 6 setae at NIV to NVI (Figure 6A–F). The endopod is 1- segmented; at NI it carries 6 setae: 2 naked setae proximally, 2 naked setae at mid-margin and 2 plumose setae distally. At NII it carries 1 naked and 2 spinulate setae proximally, 2 naked setae at mid-margin and 3 plumose setae distally. At NIII and NIV it carries 3 spinulate setae proximally, 2 naked setae at mid-margin and 1 naked plus 3 plumose setae distally. The numbers of endopodal setae remain the same at NV and NVI but the 2 mid-margin setae are plumose at NVI.
Post-naupliar stages
Post-naupliar stages comprise six copepodid stages, with the sixth being the adult. The first three stages CoI–CoIII are the same for both sexes; sexual dimorphism is first detected externally at CoIV; in each sex there are two stages (males CoIV M and CoV M and females CoIV F–CoV F), prior to the adult males (M) and females (F) (Figure 7A–I).
Body gymnoplean in dorsal aspect (Figure 7). At CoI the body comprises 6 segments (Figure 7A), a 4-segmented prosome and a 2-segmented urosome (Figure 10A). At the moult to CoII, the anteriormost urosomite (the fourth pedigerous somite) becomes incorporated into the prosome (Figure 7B) and a new somite (the fifth pedigerous somite) is expressed just anterior to the last body division bearing the anus, so the urosome remains 2-segmented (Figure 10B). At the next moult (to CoIII), the fifth pedigerous somite becomes incorporated into the prosome and fuses with the fourth to form a double-somite, so the prosome still appears to be 5-segmented (Figure 7C). This is the adult configuration of the prosome in both sexes; the cephalosome and first pedigerous somite are separate; the second and third pedigerous somites are free and the fourth and fifth pedigerous somites are fused. At the same moult, a new somite (the genital somite) is expressed anterior to the last body division bearing the anus, so the urosome appears 2-segmented (Figure 10C). At CoIII, the 2-segmented urosome of both sexes comprises the newly budded-off genital somite plus the posterior division bearing the anus. In the female CoIV (Figures 7D, 10E–F) the apparent urosomal segmentation remains the same although the anterior urosomite increases in length. At the moult to CoV the female adds an additional urosomite (Figures 7F, 10G), budded off anterior to the anal somite, and this segmentation is the same as in the adult female (Figures 7G, 10I,J). In the male, a new urosomite is budded off anterior to the anal somite at the moult to CoIV (Figures 7E, 10D), producing a 3-segmented urosome; and another somite is budded off anterior to the anal somite at the next moult to CoV (Figures 7H, 10H) resulting in a 4-segmented urosome.Another somite is budded off at the final moult resulting in the formation of the 5-segmented urosome of the adult male (Figures 7I, 10K,L). The body lengths of the copepodid stages (Figure 3) increase linearly from 330 µm (CoI) to 670 µm (CoIV F and CoV M).
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. At CoI each ramus is armed with 4 setae, an additional seta is added at CoII which has 5 setae, and another at CoIII, and this setation remains the same through to the adult, which has 1 lateral, 1 ventral and 4 distal setae (Figure 10A–L).
The antennule comprises 10 articulated segments at CoI (Figure 12A) armed as follows: segment 1 (ancestral segments I–V) 1 seta; segment 2 (ancestral segments VI–XVI) 1 + aesthetasc (ae); segment 3 (ancestral segments XVII–XX) 1 seta; segment 4 (ancestral XXI) 1 + ae; segment 5 (ancestral XXII) unarmed; segment 6 (ancestral XXIII) 1 seta; segment 7 (ancestral XXIV) 1 seta (posterior margin); segment 8 (ancestral XXV) 2 setae + ae (1 seta on posterior margin, one on anterior margin); segment 9 (ancestral XXVI) 2 setae (1 posterior and 1 anterior); and segment 10 (ancestral XXVII–XXVIII) 4 + ae.
At CoII the antennule comprises 15 segments (Figure 12B); the apical array of 7 segments are as in CoI (ancestral segments XXI to XXVII–XXVIII), with the increase in segment number due to differentiation in the proximal part of the antennule; expressed segments armed as follows: segment 1 (ancestral I–V) 1 seta; segment 2 (ancestral VI–IX) 1 + ae; segment 3 (ancestral X–XII) 1 + ae; segment 4 (ancestral XIII–XIV) 1; segment 5 (ancestral XV–XVI) 1 + ae; segment 6 (ancestral XVII–XVIII) 1; segment 7 (ancestral XIX) unarmed; segment 8 (ancestral XX) 1; segment 9 (ancestral XXI) 1 + ae; segment 10 (ancestral XXII) 1; segment 11 (ancestral XXIII) 1 seta; segment 12 (ancestral XXIV) 2 setae (1 posterior and 1 anterior); segment 13 (ancestral XXV) 2 setae + ae (1 posterior and 1 anterior); segment 14 (ancestral XXVI) 2 setae (1 posterior and 1 anterior); segment 15 (ancestral XXVII–XXVIII) 4 + ae. The only changes in the distal array of 7 segments are the addition of a seta to segment 10 (ancestral XXII) and the addition of the anterior seta to segment 12 (ancestral XXIV). There are no further setal additions to the apical 7 segments during development.
At CoIII the antennule comprises 17 segments (Figure 12C); the apical 7 segments are as in CoII (ancestral XXI to XXVII–XXVIII), with 2 additional segments expressed in the proximal part of the antennule; expressed segments armed as follows: segment 1 (ancestral I–V) 1 seta; segment 2 (ancestral VI–IX) 2 + ae; segment 3 (ancestral X–XII) 2 + ae; segment 4 (ancestral XIII) 1; segment 5 (ancestral XIV–XV) 2; segment 6 (ancestral XVI) 1 + ae; segment 7 (ancestral XVII) 1; segment 8 (ancestral XVIII) 1; segment 9 (ancestral XIX) 1 and segment 10 (ancestral XX) 1; segments 11 to 17 (ancestral XXI to XXVII–XXVIII) armed as in CoII.
In the female CoIV the antennule comprises 18 segments (Figure 13A), with 1 additional segment expressed in the proximal part: expressed segments armed as follows: segment 1 (ancestral I–V) 1 seta; segment 2 (ancestral VI–IX) 4 + 2ae; segment 3 (ancestral X) 2; segment 4 (ancestral XI–XII) 2 + ae; segment 5 (ancestral XIII) 1; segment 6 (ancestral XIV–XV) 2; segment 7 (ancestral XVI) 1 + ae; segment 8 (ancestral XVII) 1; segment 9 (ancestral XVIII) 1 and segment 10 (ancestral XIX) 1; segment 11 (ancestral XX) 1; segments 12 to 18 (ancestral XXI to XXVII–XXVIII) armed as in CoII.
The segmentation of the antennule of the CoV and adult female is unchanged, remaining 18-segmented (Figure 13B, C). At the moult to CoV 1 seta is added to segment 2, and 1 aesthetasc is added to segment 6 (derived from ancestral XIV) and to segment 9 (ancestral XVIII).
At the final moult from CoV to adult female the expressed segmentation of the antennule remains unchanged but two setae are added, 1 each to segments 2 and 4.
The antenna (Figure 16) is biramous, with the endopod much longer than the exopod in all stages. The coxa is armed with 1 medial margin seta in all copepodid stages. The endopod is 2-segmented at CoI to CoIII but is completely fused to the basis, forming an elongate allobasis armed with 5 setae at CoI (Figure 16A) and CoII (Figure 16B), with 1 seta at the inner distal corner and 4 setae arrayed along the inner margin. The compound distal endopodal segment is armed with total of 9 setae along its inner and distal margins. The exopod is indistinctly segmented, comprising a long proximal segment plus 3 short, incompletely-expressed segments distally; armed with total of 7 setae in CoI and CoII.
At CoIII (Figure 16C) 1 seta is added to the array of plumose setae along the inner margin of the allobasis, bringing the total to 5 plus the distal seta; 2 setae are added to the compound distal segment of endopod, so that the total armature is now 4 naked setae located distally on the inner margin plus 7 plumose setae around the apex. The exopod gains a seta, bringing the total to 8 setae.
At CoIV (Figure 16D) 1 seta is added to the array of plumose seta along the inner margin of the allobasis, bringing the total to 6 plus the distal seta; the compound distal segment of the endopod has divided, so that the elongate middle segment bears 5 setae located distally on the inner margin, and the small apical segment carries 7 plumose setae around the apex. The setation of the exopod is unchanged at 8 setae.
At CoV (Figure 16E) 1 further seta is added to the array on the inner margin of the allobasis, bringing the total to 7 plus the distal seta; the elongate middle endopodal segment gains an additional seta bringing the total to 6 setae located distally on the inner margin; the small apical segment is unchanged, with 7 plumose setae around apex. A transverse row of spinules extending onto the outer distal margin, is present distally on the allobasis, and a row of setules is present distally on the outer margin of the middle endopodal segment. The setation of the exopod is unchanged at 8 setae. At the moult to adult 1 seta is added to the allobasis and 1 seta to the middle endopodal segment.
The mandible (Figure 17) comprises a large coxa, which forms the gnathobase medially, plus a biramous mandibular palp in all copepodid stages including the adult. The cutting edge of the gnathobase is produced into 8–9 heterogeneous teeth. Segmentation within the palp is not expressed in stages CoI to CoIII; the palp forms an inner lobe (the endopod) bearing 2 inner setae plus 6 distal setae at Co I (Figure 17A) and an outer lobe (the exopod) armed with 6 setae distally. The proximal part representing the basis is longer than wide and armed with a single seta located distal on the margin. The basis carries just this single inner seta in all stages.
At the moult to CoII a single seta is added distally on the endopod, bringing the total to 7 setae (Figure 17B). There is no change to the numbers of setae at CoIII (Figure 17C). The palp segmentation is expressed more clearly at CoIV (Figure 17D): the endopod is 2-segmented, with the first segment bearing 2 short setae and the second 8 (one additional seta added at moult from CoIII); the exopod now appears indistinctly 4-segmented and is armed with 1,1, 2, 2 setae. The setation and segmentation of both rami appears unchanged at CoV (Figure 17E); but a row of small setules is present distally on the inner margin of the basis. At the moult to adult the second endopodal segment gains 1 seta, bringing the total to 9, and the exopod now appears indistinctly 5-segmented with an armature of 1,1,1,1,2.
The maxillule is a multilobate limb throughout development (Figure 18); 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. There are changes in setation on some of these lobes through the copepodid stages, but the setation of the coxal endite (3 setae), basal endite (1 seta), and basal exite (1 reduced seta) remains constant from CoI to adult. The apical lobe (exopod) carries 7 setae along its outer and distal margins, arranged with 2 proximal setae slightly separated from the 5 distal setae. The total number of setae remains stable through to the adult but at the moult from CoV (Figure 18E) to adult (Figure 18F) some traces of segmentation appear distally and the 5 distal setae originate on these segments. The praecoxal arthrite bears 7 elements at CoI (Figure 18A), 8 at CoII (Figure 18B), and 9 elements from CoIII (Figure 18C) to adult (Figure 18F). The coxal epipodite is represented by 4 setae at CoI, 6 setae at CoII, 8 setae at CoIII, and 9 setae from the CoIV (Figure 18D) to the adult.
The maxilla is uniramous and unsegmented through early development, but with traces of incomplete segmentation appearing at the final moult to adult (Figure 19). There are changes in setation during the copepodid phase: at CoI the maxilla carries 12 setae (Figure 19A), 3 setae are added at the moult to CoII (Figure 19B), no setae are added at CoIII (Figure 19C) or CoIV (Figure 19D), but at the moult to CoV (Figure 19E) a seta is added bringing the total to 16 setae. The adult maxilla carries a total of 19 setae.
The maxilliped (Figure 20) is 4-segmented throughout the copepodid phase. The proximal segment (syncoxa) carries 4 spinulate setae at CoI (Figure 20A); at the moult to CoII a further seta is added (Figure 20B) and this total of 5 setae remains unchanged from CoII to CoV (Figure 20E); at the final moult, another seta is added bringing the total to 6 setae (Figure 20F); 3 of the spinulate setae on the syncoxa are extremely long (twice as long as the entire limb) at all stages. The basis is oval in shape; it is unarmed in CoI but from CoII onwards it bears 1 seta proximally on the inner margin. The endopod is 2-segmented and the distal segment carries 2 unequal apical setae in all stages; the proximal segment is armed with 1 spiniform seta at CoI, and 3 spiniform setae at all stages from CoII to the adult.
The segmentation and the armature of the swimming legs 1–4 are presented in Figures 21–24. Legs are biramous in all copepodid stages as well as in the adult. Leg 3 is biramous from CoII (Figure 23) and leg 4 is biramous from CoIII (Figure 24). In all legs the coxa is unarmed. The basis is unarmed in legs 1 and 2, but in the adult both leg 3 (Figure 23E) and leg 4 (Figure 24D) each gain an outer seta on the basis at the final moult from CoV.
The endopod of leg 1 is 1-segmented at the CoI stage (Figure 21A) and becomes 2-segmented at the moult to CoII (Figure 21B); the segmentation is unchanged from CoII through to the adult. At CoI the endopod is armed with 1 outer distal seta, 3 distal margin setae and 2 inner margin setae; at the moult to CoII a third seta appears on the inner margin, and the proximalmost seta on this margin now arises on the first segment of the 2-segmented endopod. The setation of the second segment remains unchanged through to the adult.
The exopod of leg 1 is 1-segmented at CoI (Figure 21A), 2-segmented from stages CoII to CoIV (Figure 21B– D), and 3-segmented from CoV (Figure 21E) to the adult (Figure 21F). Using the apical seta (with its serrate outer margin and plumose inner margin) as a marker, the exopod of CoI is armed with 4 outer margin setae, an apical seta, and 3 inner setae (Figure 21A). At the moult to CoII, 2 inner margin setae are added, 1 on the newly differentiated first exopodal segment and 1 proximally on the compound second exopodal segment (Figure 21B). The setation is unchanged at CoIII and CoIV. At the moult to CoV (Figure 21E) 1 further new seta is added proximally on the inner margin of the newly differentiated third exopodal segment. No setae are added at the moult from CoV to adult (Figure 21F).
The endopod of leg 2 is 1-segmented at CoI (Figure 22A) and its segmentation is unchanged until CoIV (Figure 22D); at the moult to CoV (Figure 22E) the endopod becomes 2-segmented, with the proximal segment representing a compound segment derived from ancestral segments 1 and 2; the segmentation is unchanged in the adult (Figure 22F). At CoI the endopod is armed with 1 outer distal seta, 3 distal margin setae and 2 inner margin setae, as for leg 1. At the moult to CoII (Figure 22B) a third seta appears on the inner margin, and at the moult to CoIII (Figure 22C) a fourth inner seta is added. The setal number is unchanged in the CoIV but the distribution of the setae, with 1 outer distal seta, 5 distal and inner distal setae, and 2 proximal inner setae is more distinct (Figure 22D). At CoV the newly differentiated compound proximal segment of the endopod is armed with 2 inner setae and the short distal segment carries the outer seta plus a total of 6 inner and distal setae, 1 of which was added at the moult from CoIV. The endopod of the adult is unchanged from CoV.
The exopod of leg 2 is 1-segmented at CoI (Figure 22A), 2-segmented at stages CoII and CoIII (Figure 22B–C), and 3-segmented from CoIV (Figure 22D) to adult (Figure 22F). Using the apical seta (serrate outer margin and plumose inner margin) as a marker, the exopod of CoI is armed with 2 spinous processes on the outer margin, an apical seta, and 3 inner setae (Figure 22A). At the moult to CoII, the proximal spinous process on the outer margin is now located on the newly differentiated first segment and a fourth seta is added on the inner margin of the compound distal exopodal segment (Figure 22B). At the moult to CoIII, an inner seta is added on the newly differentiated first segment and while the compound distal exopodal segment gains an outer spinous process and a fifth seta on the inner margin (Figure 22C). At the moult to CoIV (Figure 22D) the compound distal exopodal segment differentiates into the second and third exopodal segments: the second segment is armed with 1 outer spinous process and 1 inner seta; the third segment with 1 outer spinous process, an apical seta plus 4 inner setae, so the total number of setal elements is the same as in the preceding CoIII stage. At the moult to CoV (Figure 22E) a single inner seta is added to the third exopodal segment and the setation is then unchanged into the adult (Figure 22F).
The endopod of leg 3 is 1-segmented at CoII (Figure 23A) and its segmentation is unchanged until the moult to CoV (Figure 23D) when it becomes 2-segmented, with the proximal segment representing a compound segment derived from ancestral segments 1 and 2; the endopodal segmentation is unchanged in the adult (Figure 23E). At CoII the endopod is armed with 1 outer distal seta, 3 distal margin setae and 2 inner margin setae. At the moult to CoIII (Figure 23B) a third seta appears on the inner margin, at the moult to CoIV (Figure 23C) a fourth inner seta is added, and at the moult to CoV a fifth seta is added. At CoV (Figure 23D) the newly differentiated compound proximal segment of the endopod is armed with 2 inner setae and the short distal segment carries the outer seta plus a total of 6 inner and distal setae, the most proximal of which was added at the moult from CoIV. The endopod of the adult is unchanged from CoV. The outer basal seta appears at the final moult to adult.
The exopod of leg 3 is 1-segmented at CoII (Figure 23A), 2-segmented at CoII (Figure 23B), and 3-segmented from CoIII (Figure 23C) to adult (Figure 23E). Using the apical seta as a marker, the exopod of CoII is armed with 2 spinous processes on the outer margin, an apical seta, and 3 inner setae (Figure 23A). At the moult to CoIII, the proximal spinous process on the outer margin is now located on the newly differentiated first segment and a fourth seta is added on the inner margin of the compound second exopodal segment (Figure 23C). At the moult to CoIV (Figure 23C) the first exopodal segment gains an inner seta; the compound distal exopodal segment differentiates into the second and third exopodal segments: the second segment is armed with 1 outer spinous process and 1 new inner seta; the third segment has 1 outer spinous process, an apical seta, plus 4 inner setae. At the moult to CoV (Figure 23D) a single inner seta is added to the third exopodal segment and the setation is unchanged in the adult (Figure 23E).
The endopod of leg 4 is 1-segmented at CoIII (Figure 24A) and its segmentation is unchanged until the moult to CoV (Figure 24C) when it becomes 2-segmented, with the proximal segment representing a compound segment derived from ancestral segments 1 and 2; the endopodal segmentation is unchanged in the adult (Figure 24D). At CoIII the endopod is armed with 1 outer distal seta, 3 distal margin setae and 2 inner margin setae. At the moult to CoIV (Figure 24B) a third seta appears on the inner margin. At the moult to CoV (Figure 24C) 2 more setae are added to the inner margin; 1 seta on the newly differentiated compound proximal segment of the endopod which is armed with 3 inner setae, and 1 on the short distal endopodal segment which now carries the outer seta plus a total of 5 inner and distal setae. The endopod is unchanged in the adult (Figure 24D). The outer basal seta appears at the final moult to adult.
The exopod of leg 4 is 1-segmented at CoIII (Figure 24A), but 3-segmented from CoIV (Figure 24B) to the adult (Figure 24D). Using the apical seta as a marker, the exopod of CoIII is armed with 2 spinous processes on the outer margin, an apical seta, and 3 inner setae (Figure 24A). At the moult to CoIV (Figure 24B), the proximal spinous process on the outer margin is now located on the newly differentiated first exopodal segment; the compound distal exopodal segment differentiates into the second and third exopodal segments: the second segment is armed with 1 outer spinous process and 1 new inner seta; the third segment has 1 outer spinous process, an apical seta, plus 5 inner setae (1 of which is newly added). At the moult to CoV (Figure 24C) an inner seta is added to the first exopodal segment and another inner seta is added proximally on the third exopodal segment. The exopodal setation is unchanged in the adult (Figure 24D).
The antennules of the male are as in the female for stages CoI to CoIII. The antennule of male CoIV (Figure 14A) comprises 20 segments and the expressed segments are armed as follows: segment 1 (ancestral I–V) 1 seta; segment 2 (ancestral VI–VII) 3 + ae; segment 3 (ancestral VIII–IX) 2 + ae; segment 4 (ancestral X) 2 setae; segment 5 (ancestral XI) 1+ ae; segment 6 (ancestral XII) 1; segment 7 (ancestral XIII) 1; segment 8 (ancestral XIV) 2 + ae; segment 9 (ancestral XV) 1; segment 10 (ancestral XVI) 1 + ae; segment 11 (ancestral XVII–XVIII) 1; segment 12 (ancestral XIX) 1; segment 13 (ancestral XX) 1; segments 14 to 20 (ancestral XXI to XXVII–XXVIII) armed as in CoII.
The antennule of male CoV (Figure 14B) comprises 21 segments due to the division of the double segment 11 (ancestral XVII–XVIII) of the preceding stage. The expressed segments are armed as follows: segment 1 (ancestral I–V) 1 seta; segment 2 (ancestral VI–VII) 3 + ae; segment 3 (ancestral VIII–IX) 3 + ae; segment 4 (ancestral X) 2 setae; segment 5 (ancestral XI) 1+ ae; segment 6 (ancestral XII) 1; segment 7 (ancestral XIII) 1; segment 8 (ancestral XIV) 2 + ae; segment 9 (ancestral XV) 1; segment 10 (ancestral XVI) 1 + ae; segment 11 (ancestral XVII) 1; segment 12 (ancestral XVIII) 1 + ae; segment 13 (ancestral XIX) 1; segment 14 (ancestral XX) 1; segments 15 to 20 (ancestral XXI to XXVII–XXVIII) armed as in CoII.
Antenna, mouthparts and swimming legs 1–4 identical to those of female.
description: Published as part of Kršinić, Frano & Boxshall, Geoff A., 2024, Redescription of Acartia (Acanthacartia) italica Steuer, 1910 (Copepoda, Calanoida), and description of the developmental stages from the small saline Lake Rogoznica, Adriatic Sea, pp. 539-571 in Zootaxa 5543 (4) on pages 541-566, DOI: 10.11646/zootaxa.5543.4.3, http://zenodo.org/record/14386678