CALIGUS TURKIYENSIS N. SP. (COPEPODA: CALIGIDAE) ON THE FLATHEAD GREY MULLET, MUGIL CEPHALUS (LINNAEUS) (MUGILIFORMES: MUGILIDAE) FROM THE SEA OF MARMARA, TURKEY

Description

Adult female: Cephalothorax subcircular, dorsoventrally flattened, lateral zones of dorsal cephalothoracic shield associated with welldeveloped marginal membranes. Body consists of a caligiform cephalothorax shield, a fourth pedigerous somite, a genital complex and an indistinctly 2-segmented abdomen with paired caudal rami. Total body length 3.79 mm (3.134.61, n = 7) (Fig. 2a, 3a). Dorsal cephalothoracic shield subcircular, longer at 1.82 mm (1.52-2.01) than wide 1.61 mm (1.34-1.73). Fourth pedigerous somite is wider at 0.46 mm (0.24-0.61) than long 0.23 mm (0.14-0.32), distinctly separated from the cephalothorax and genital complex. Genital complex subcircular, is slightly wider at 1.04 mm (0.77-1.52) than long 0.94 mm (0.741.31), about 1.6 times longer than the abdomen and with nonlobate posterolateral corners of genital complex. Abdomen subrectangular, indistinctly with two somites, first abdominal somite slightly wider at 0.31 mm (0.21-0.41) than long 0.18 mm (0.12-0.22), anal somite longer at 0.41 mm (0.280.48) than wide 0.33 mm (0.28-0.42). Egg sac 2.11 mm (1.82-2.51) long by 0.36 mm (0.31-0.42) wide.

Antennule (Fig. 3b) 2-segmented; proximal segment distinctly larger than distal, armed with 24 setae; distal segment armed with isolated subterminal seta on posterior margin and 11 naked setae plus two aesthetascs around the apex. Antenna (Fig. 3f, 6e) uniramous, 3-segmented; proximal segment subrectangular with rounded margins and a short process; middle segment subrectangular and armed with a large corrugated adhesion pad on the dorsal surface; terminal segment forming a recurved claw armed with a seta near the middle area and posterior margin. Post-antennal process (Fig. 3f, 6g) well-developed, slender and slightly curved, ornamented with two trisensillate papillae on the basal part and a single similar trisensillate papilla on the adjacent ventral cephalothoracic surface near the base of the post-antennal process. Mandible (Fig. 3c, 6m) stylet-like, armed with 13 marginal teeth on inner side near the apex. Maxillule (Fig. 3h, 6k) comprising an anterior papilla bearing three naked setae (one medial long seta and two lateral small setae), and an anterior process with folding, and posterior process slender with rounded margin. Maxilla (Fig. 3g) 2-segmented and brachiform; proximal segment (lacertus) unarmed; distal segment (brachium) slender, bearing subterminal hyaline membrane on the inner margin plus short canna and long calamus distally. Maxilliped (Fig. 3e, 6a) subchelate, protopodal segment (corpus) elongate and bearing a slight expansion on myxal surface; distal subchela representing endopodal segments plus claw; small seta at the concave margin of claw base. Sternal furca (Fig. 3d, 6c) with subrectangular box, elongated and parallel tines with little divergence. Leg 1 (Fig. 4a) biramous with sympods joined by a slender intercoxal sclerite; sympod with inner and outer plumose seta, plus a setule; and endopod represented by a process on the posterior margin of basis, bearing two-minute vestigial setae on the apex. Exopod 2-segmented, with first exopodal segment robust, about 2.7 times longer than wide, armed with a small outer spine at the distal corner and ornamented with a row of setules along the mid-section of the posterior margin. Distal exopodal segment with three plumose setae posteriorly plus four distal margin elements; spine 1 (outermost) and seta 4 smooth and longer than spines 2-3; spines 2 and 3 about equal in length, both lacking accessory process and arcuated with blunt ends. Leg 2 (Fig. 4b) biramous, with distinct coxa and basis; coxa short, bearing a long plumose inner seta and a sensillium on the ventral surface; basis armed with a short naked seta on the outer distal corner plus extensive marginal membrane along the posterior margin and a sensillium near the mid-length of the anterior margin. Exopod 3-segmented: first exopodal segment with inner plumose seta, an outer spine, extending to the middle of the third exopodal segment and with a row of setules on the inner margin; the second exopodal segment is the smallest, with an inner plumose seta and an outer distal spine and not extending across to the anterior margin of the third segment. Third exopodal segment with three outer spines and five inner plumose setae; first spine simple and smallest; second spine slightly longer than first spine and third spine with an outer marginal membrane and fine setules along the inner margin. Endopod 3-segmented; first endopodal segment subrectangular, armed with an inner plumose seta and ornamented with a row of setules along the outer margin; second segment elongated, armed with two inner plumose setae plus ornamented with a row of setules along the outer margin; third segment smallest, with six plumose setae. Leg 3 (Fig. 4c) protopodal part flattened and joined by plate-like intercoxal sclerite, forming an apron ornamented with marginal membrane posteriorly and along the lateral margin anterior to the exopod: bearing inner plumose seta at the junction with intercoxal plate and an outer plumose seta dorsal to the base of the exopod; sensillae located adjacent to the inner coxal seta and adjacent to the origin of endopod. Exopod 3-segmented: first segment with a large, recurved outer spine; a hyaline flap and sensillium along the corner of spine; second segment with an outer spine, inner plumose seta and setules along outer margin; the third segment with three outer spines (third spine slightly longer than the other two) and four short plumose setae. Endopod 2-segmented: first segment is armed with a long inner plumose seta; second segment is armed with six plumose setae, ornamented with rows of setules along the outer margin. Leg 4 (Fig. 4d, 6o) uniramous. Protopodal segment with an outer seta derived from the basis. Exopod 2-segmented; first segment bearing a short, slender, outer distal spine, not extending to the middle part of second exopodal segment; second segment with three apical spines increasing in length from outer to inner; first spine slightly shorter than second and third spine three times as long as. Leg 5 (Fig. 4e) is represented by three plumose setae. Setal and spinal formula of 1-4 legs are given in Table II. Caudal ramus (Fig. 4f) subrectangular, longer 0.19 mm (0.13-0.27) than wide 0.14 mm (0.10-0.25), each armed with three distal setae the longest on the outer margin, a median size seta, and other the two located opposed, and with a row of setules on inner margin.

Adult male: Cephalothorax subcircular, dorsoventrally flattened, lateral zones of dorsal cephalothoracic shield associated with welldeveloped marginal membranes. Body consists of a caligiform cephalothorax shield, a fourth pedigerous somite, a genital complex and 1-segmented abdomen with paired caudal rami. Total body length 3.67 mm (3.30-4.69, n = 7) (Fig. 2c, 5a). Dorsal cephalothoracic shield subcircular, is slightly longer 2.12 mm (1.82-2.71) than wide 1.75 mm (1.52-2.22). Fourth pedigerous somite at wider 0.49 mm (0.41-0.61) than long 0.29 mm (0.21-0.35), distinctly separated from the cephalothorax and genital complex. Genital complex subcircular, is slightly at wider 0.69 mm (0.56-0.92) than long 0.56 mm (0.46-0.72), and about 1.2 times longer than abdomen. Abdomen subrectangular, 1-segmented, longer at 0.46 mm (0.41-0.60) than wide 0.34 mm (0.30-0.42). Caudal ramus subrectangular, longer at 0.23 mm (0.200.31) than wide 0.13 mm (0.11-0.22), each armed with six plumose setae. Antennule, mandible, post-antennal process and maxilla as in female. Maxilliped (Fig. 5b, 6i) protopod (corpus) is slightly swollen and armed with one small process at distal part and one big process as bifid at posterior part of myxal surface opposing tip of subchela; distal subchela armed with a short seta at the concave margin of claw base and a spine at posterior margin. Antenna (Fig. 5c) 3-segmented; proximal segment elongated and unarmed; middle segment reflexed, swollen proximally, with corrugated adhesion pads on medial and distal surfaces; distal segment with four plates on trifid direction and with basal seta. Maxillule (Fig. 5d) comprising an anterior papilla bearing three naked setae (one long and two small) and reduced posterior process. Legs 1 to 4, as in female. Leg 5 and 6 (Fig. 5e) are represented by three plumose setae and a minute spine, respectively.

Remarks: The report of C. mugilis from M. cephalus caught in Bandırma Bay (Sea of Marmara) by Alaş & Öktener (2017) is erroneous according to Özak (2020) for the following reasons: the female had an abdomen as long as the genital complex; the female maxilliped had a distinct, subtriangular myxal process; the posterolateral corners of the genital complex were indistinctly lobate and did not extend beyond the posterior margin of the genital complex. This study provided an opportunity to collect and examine the specimens of Alaş & Öktener (2017) again. The morphology of the new species appears to have the closest similarity to the four species Caligus curtus Müller O.F., 1785, Caligus dicentrarchi Cabral & Raibaut, 1986, C. minimus and C. mugilis (Table IV). Caligus mugilis was described for the first time from the mucous membrane of the mouth of M. cephalus from Portoferraio, Italy by Brian (1935), but he considered it to be a subspecies of Caligus minimus and named it as Caligus minimus var. n. mugilis. Later, Raibaut & Ben Hassine (1977) accepted C. mugilis as a different species from Chelon labrosus (Risso, 1827) and described it from only female specimens. They also compared females of C. mugilis from C. labrosus and C. minimus from Dicentrarchus labrax (Linnaeus, 1758) in Tunisia. The female of the new species differs from C. mugilis in having a smaller body at 3.79 mm (5.33 mm in C. mugilis); a genital complex which is about 1.6 times longer than the abdomen (3.2 times in C. mugilis); an abdomen with two indistinct somites (one somite in C. mugilis); tines of sternal furca little divergent, slightly elongated (divergent, short tines in C. mugilis); number of teeth on mandible as 13 (12 in C. mugilis); posterolateral corners of genital complex indistinctly lobate not extending to middle or anterior of the abdomen (distinctly lobate, extending slightly beyond the middle of abdomen in C. mugilis); ratio of length/anterior margin of maxillule endopodite is 1.45 (1.1 in C. mugilis); myxal surface of maxilliped with a slight process (absent in C. mugilis); and ratio of first spine/third spine on fourth leg is 3.2 (3.4 in C. mugilis). The male of the new species could not be compared as the male of C. mugilis was not described. The other species reported from M. cephalus is Caligus minimus which was described on D. labrax by Otto (1821). The female of the new species differs from C. minimus in having a smaller body 3.79 mm in comparison with 4.38 mm in C. minimus; genital complex is about 1.6 times longer than abdomen (2.3 times in C. minimus); abdomen with indistinctly two somites (one somite in C. minimus); tines of sternal furca are little divergent, slightly elongated (slightly divergent short in C. minimus) (Fig. 6d); number of teeth on mandible is 13 (12 teeth in C. minimus) (Fig. 6m); posterolateral corners of genital complex indistinctly lobate not extending to middle or anterior of the abdomen (distinctly lobate, extend slightly beyond one third of abdomen in C. minimus); terminal segment of antenna and postantennal process slightly recurved (strongly recurved in C. minimus) (Fig. 6f, h); ratio of length/anterior margin of maxillule endopo.

Male of the new species differs from C. minimus in having a smaller body 3.67 mm (4-5 mm in C. minimus); myxal surface of maxilliped with one small process in distal and one large bifid process in proximal (one large process in proximal of C. minimus) (Fig. 6j); terminal segment of antenna with quadrifid plate and a basal seta (quadrifid plate in C. minimus).

Caligus curtus was described from Merlangius merlangus (Linnaeus, 1758) in Denmark and Norway waters by Müller (1785). It can be distinguished from C. turkiyensis n. sp. in having: a greater body, 8.7 mm in comparison to 3.79 mm; a genital complex about 2.5 times longer than the abdomen (1.6 times in C. turkiyensis n. sp.); an abdomen with one somite (indistinctly two somites in C. turkiyensis n. sp.); tines of sternal furca slightly divergent, short parallel (little divergent, slightly elongated in C. turkiyensis n. sp.); number of teeth on mandible 12 (13 teeth in C. turkiyensis n. sp.); posterolateral corners of genital complex distinctly lobate, extend slightly beyond one third of abdomen (indistinctly lobate not extending to middle or anterior of the abdomen in C. turkiyensis n. sp.); terminal segment of antenna and postantennal process strongly recurved (slightly recurved in C. turkiyensis n. sp.); ratio of length/anterior margin of maxillule endopodite of 0.8 (1.45 in C. turkiyensis n. sp.); and ratio of first spine/third spine on fourth leg of 5 (3.2 in C. turkiyensis n. sp.). Male of C. curtus differs from C. turkiyensis n. sp. in having a greater body of 7.93 mm in comparison to 3.67 mm in C. turkiyensis n. sp.; myxal surface of maxilliped with one large process in both proximal and distal (one small process in distal and one large bifid process in proximal of C. turkiyensis n. sp.); and terminal segment of antenna with bifid plate and a basal seta (quadrafid plate and a basal seta in C. turkiyensis n. sp.) and denticles on first spine of fourth leg present (absent in C. turkiyensis n. sp.). Caligus dicentrarchi was found on D. labrax farmed in Corsica and Sete by Cabral & Raibaut, 1986. The female of the new species can be differentiated from C. dicentrarchi in having: a smaller body of 3.79 mm in comparison to 6.2 mm in C. dicentrarchi; genital complex is about 1.6 times longer than the abdomen (2.6 times in C. dicentrarchi); abdomen with indistinctly two somites (one somite in C. dicentrarchi); tines of sternal furca little divergent, slightly elongated (short parallel in C. dicentrarchi); number of teeth on mandible 13 (12 teeth in C. dicentrarchi); posterolateral corners of genital complex indistinctly lobate not extending to middle or anterior of the abdomen (distinctly lobate, extend slightly beyond one-third of abdomen in C. dicentrarchi); ratio of length/anterior margin of maxillule endopodite of 1.45 (1.2 in C. dicentrarchi); myxal surface of maxilliped with a slight process (absent in C. dicentrarchi); and ratio of first spine/third spine on fourth leg of 3.2 (4.5 in C. dicentrarchi). Male of the new species differs from C. dicentrarchi in having a smaller body of 3.67 mm (6.5 mm in C. dicentrarchi); myxal surface of maxilliped with one small process in distal and one large bifid process in proximal (one large process in proximal of C. dicentrarchi); terminal segment of antenna with quadrifid plate and a basal seta (trifid plate in C. dicentrarchi). Boxshall (2018) classified some Caligus species in 5 groups according to a combination of several morphological characters, such as leg 1, 2 and 4, antenna, maxilla, and abdomen of female. These groups are Caligus bonito-group, Caligus confusus-group, Caligus diaphanus-group, Caligus macarovi-group, and Caligus productus-group. The number of these groups reached 7 with the revision of Caligus pseudorhombi-group and Caligus undulatus-group by Ohtsuka & Boxshall (2019) and Ohtsuka et al. (2020), respectively. Caligus turkiyensis n.sp. may also be closely related to the C. macarovi-group. First and second exopodal segments of 3-segmented leg 4 with I and III spines in this group are the same in the new species. The proximal segment of female antenna has a posterior process, as in this group. The new species differs from the C. macarovi-group: female abdomen is 2-segmented indistinctly in the new species, but group carries 1-segmented. Distal of maxilla brachium in this group has marginal serrations, but is absent in the new species. Structure of setal and spinal of leg 1 in new species is similar to the rest group. This species has also the distal exopodal segment of leg 1 bears 3 plumose setae and 4 distal elements. Spines 1-3 are all subequal in length and seta 4 is markedly longer than spines in this group. Spine 1 (outermost) and seta 4 are smooth and longer than spines 2-3; spines 2 and 3 are about equal in length in new species. Only spines 2 and 3 carry accessory processes in this group, but spines 2 and 3 both lack accessory process and arcuated with blunt ends. Many morphological characters of the new species are different from the C. macarovi-group. Therefore, it is likely that it does not belong to this group.