Caligus izmiriensis, Özak & Kurt & Kamanli & Akbulut & Yanar & Boxshall, 2024

Özak, Argun Akif, Kurt, Tuba Terbiyik, Kamanli, Seyit Ali, Akbulut, Gürkan, Yanar, Alper & Boxshall, Geoffrey A., 2024, Two new species of planktonic Caligus O. F. Müller 1785 (Copepoda: Caligidae) from Türkiye with an updated review and checklist of planktonic caligids, Zootaxa 5437 (3), pp. 301-335 : 305-315

publication ID	https://doi.org/ 10.11646/zootaxa.5437.3.1
publication LSID	lsid:zoobank.org:pub:F06B9D4F-B890-41E2-AC14-9C7DD717DFE8
DOI	https://doi.org/10.5281/zenodo.10997519
persistent identifier	https://treatment.plazi.org/id/B6978259-447A-4470-9D74-E1868246E546
taxon LSID	lsid:zoobank.org:act:B6978259-447A-4470-9D74-E1868246E546
treatment provided by	Plazi
scientific name	Caligus izmiriensis
status	sp. nov.

Treatment

Caligus izmiriensis sp. nov.

LSIDurn:lsid:zoobank.org:act: B6978259-447A-4470-9D74-E1868246E546

Type material

Holotype adult female stored in collections of the Natural History Museum, London (Reg, No,. NHMUK 2022 . 201). Type Locality: Stn ILBSW1 ; Ildır Bay, İzmir, Türkiye (38°23ʹ38.69ʺN 26°23ʹ55.95ʺE): depth 60 m; date 28.02.2020. GoogleMaps

Paratype young female stored in the collections of Aquatic Parasitology Museum of the Faculty of Fisheries, University of Çukurova (CUMAP), Adana, Ţrkiye (Reg. No. CUMAPCOP/2023. Locality: Stn S3; Akarca Cape, Seferihisar (Aegean Sea, Türkiye) (38°09ʹ40.13ʺN; 26°48ʹ35.70ʺE): depth 10 m; date 13.06.2020.

Allotype adult male stored in collections of the Natural History Museum, London (Reg, No,. NHMUK 2022. 202). Type Locality: Stn Sta20; İzmir Bay, off Urla (Aegean Sea, Türkiye) (38°27ʹ07.41ʺN; 26°51ʹ19.37ʺE): depth 50 m; date 07.05.2021.

Additional material: 1 young adult female and 1 adult male from İzmir Bay were prepared for confocal laser scanning microscopy; and were eventually dissected to allow scanning of individual limbs.

Etymology: The species name refers to the type locality.

Description ( Figs. 1‒7 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 ).

Adult female ( Fig. 1A View FIGURE 1 ). Body typical for the genus comprising dorsal cephalothoracic shield, free fourth pedigerous somite, genital complex, and 1-segmented abdomen. Total body length 2.73 mm measured from midanterior margin of frontal plate to posterior end of caudal rami, excluding caudal setae; adult female 1.1 times longer than total body length of young female ( Fig.1B View FIGURE 1 ). Dorsal cephalothoracic shield longer than wide (1.32 × 0.93 mm) with slightly convex lateral margins, posterior part about 2 times wider than anterior; frontal plate narrow, bearing pair of large lunules ventrally, ornamented with strip of narrow marginal membrane; thoracic zone of shield slightly wider than long (0.69 × 0.75 mm) with posterior margin forming posterior sinuses on either side, each sinus bearing flap-like hyaline membrane, posterior edge of thoracic zone extending beyond posterior margins of lateral zones. Dorsal cephalothoracic shield comprising about 48% of total body length. Fourth pedigerous somite sub-trapezoidal, wider than long (0.17 × 0.31 mm), distinctly separated from cephalothorax and genital complex. Genital complex longer than wide (0.82 × 0.59 mm), subrectangular with parallel lateral margins; anterolateral corners rounded, posterolateral corners distinctly lobate; genital complex length about 60% length of cephalothorax; posteroventral margin with pair of flap-like processes concealing copulatory pores ( Fig. 1C View FIGURE 1 ). Free abdomen ( Fig. 1A, C View FIGURE 1 ) unsegmented, about 1.9 times longer than wide (0.34 × 0.18 mm), with parallel lateral margins. Combined length of genital complex and abdomen comprising about 87% of cephalothorax length. Caudal ramus subrectangular, longer than wide (0.10 × 0.06 mm), armed with 6 plumose setae and ornamented with fine setules along inner margin.

Young adult female ( Fig. 1B View FIGURE 1 ). Total body length 2.49–2.51 mm (n = 2). Dorsal cephalothoracic shield subrectangular with convex lateral margins, slightly longer than wide (1.28–1.34 × 0.93–0.95 mm); thoracic zone of shield slightly wider than long (0.70–0.72 × 0.76–0.79 mm), comprising about 55% of overall length of cephalothorax. Dorsal cephalothoracic shield comprising about 50% of total body length. Fourth pedigerous somite sub-trapezoidal, wider than long (0.13–0.15 × 0.33–0.34 mm), distinctly separated from cephalothorax and genital complex. Genital complex longer than wide (0.77–0.83 × 0.51–0.56 mm), elongate with convex lateral margins; maximum width in middle, about 1.5 times greater than width at posterior end; posterolateral corners indented, posterior margin v-shaped and extending back over anterior surface of abdomen ( Fig. 1B View FIGURE 1 ). Oviducts and cement glands visible inside genital complex, posteroventral margin with pair of flap-like processes concealing copulatory pores and partially concealing pair of attached spermatophores ( Fig. 1D View FIGURE 1 ). Free abdomen ( Fig. 1B, D View FIGURE 1 ) 1-segmented, longer than wide (0.36–0.41 × 0.26–0.28 mm), tapering posteriorly, anterior part about 2 times wider than posterior, lateral margins more-or-less linear. Combined length of genital complex and abdomen comprising about 88% of cephalothorax length. Caudal ramus subrectangular, about 2 times longer than wide (0.12–0.13 × 0.06–0.07 mm), armed with 6 plumose setae.

Antennule ( Fig. 1E View FIGURE 1 ) 2-segmented; proximal segment about 1.4 times longer than distal segment, armed with 25 plumose setae along anteroventral surface plus 2 naked unequal dorsal setae; distal segment cylindrical, about 2.5 times longer than wide, armed with 1 subterminal seta on posterior margin and 11 naked setae plus 2 aesthetascs around apex.

Antenna ( Fig. 1F View FIGURE 1 ) uniramous, 3-segmented; proximal segment lacking posterior process; middle segment subrectangular, 1.5 times longer than wide and unarmed; distal subchela tapering towards sharply pointed curved claw, armed with small distal seta located at mid-length and large, papilliform, cuticular swelling proximally bearing tiny apical seta. Minute papilla-like process bearing tiny denticle at apex and single sensilla present on ventral cephalothoracic surface near proximal segment ( Fig. 1F View FIGURE 1 , arrows). Postantennal process ( Fig. 1G View FIGURE 1 ) with almost straight, blunt-tipped tine and ornamented with 2 papillae each bearing 7 sensillae, plus similar papilla with 7 sensillae located on adjacent ventral cephalothoracic surface, near base of postantennal process. Mandible ( Fig. 1H View FIGURE 1 ) stylet-like, armed with 12 inner teeth distally. Maxillule ( Fig.1I View FIGURE 1 ) comprising anterior papilla carrying 3 unequal pinnate setae and posteriorly-directed dentiform process with rounded tip. Maxilla ( Fig. 2A View FIGURE 2 ) 2-segmented, proximal segment (lacertus) large, unarmed; slender distal segment (brachium) with large subterminal hyaline membrane (flabellum) on inner margin plus short canna and long calamus distally; canna ornamented with strips of serrated membranes bilaterally, calamus with spirally arranged strips of serrated membrane. Maxilliped ( Fig. 2B View FIGURE 2 ) subchelate; protopodal segment (corpus) elongate and ornamented with single pore on myxal area, distal subchela divided by partial surface suture delimiting terminal claw; subchela bearing lateral seta plus second seta at base of terminal claw. Sternal furca ( Fig. 2C View FIGURE 2 ) (SV-IZM1) with subcircular box and straight, blunt-tipped tines positioned immediately next to each other.

Leg 1 ( Figs. 2D, E View FIGURE 2 , 3A View FIGURE 3 ) biramous with 2-segmented exopod and vestigial endopod (apparently 2-segmented). Sympod bearing lateral and inner plumose setae; ornamented with patch of tiny spinules on ventral surface ( Fig. 2D View FIGURE 2 ). First exopodal segment robust, ornamented with row of setules along posterior margin; armed with small spine at outer distal corner. Distal exopodal segment ( Figs. 2E View FIGURE 2 , 3A View FIGURE 3 ) with 3 plumose setae posteriorly plus 4 terminal elements; outermost element (spine 1) smallest; middle 2 elements (spines 2 and 3) more or less equal in length, each bearing slender, spiniform accessory process; innermost element (seta 4) distinctly longer than spines, about equal to length of segment.

Leg 2 ( Figs. 2F View FIGURE 2 , 3B View FIGURE 3 ) biramous, with distinct coxa and basis; coxa short, bearing long plumose inner seta and with sensilla on ventral surface; basis armed with short naked seta on outer distal corner plus extensive marginal membrane along posterior margin and sensilla near middle of posterior margin. Exopod ( Figs. 2F View FIGURE 2 , 3C View FIGURE 3 ) (SV-IZM2) 3-segmented; first segment with inner plumose seta, outer spine slightly curved, extending obliquely across surface of ramus and almost reaching posterior margin of second segment, spine with pecten-like membrane at base; segment ornamented with row of setules along inner margin; second exopodal segment smallest, with inner plumose seta and minute outer spine ( Figs. 2F View FIGURE 2 arrow, 3C arrow) (SV-IZM2) extending parallel to outer margin of segment: third exopodal segment with 3 spines and 5 inner plumose setae; proximalmost spine simple and smallest ( Figs. 2F View FIGURE 2 arrowhead, 3C arrowhead), second spine with marginal membrane along inner margin, and terminal spine with outer marginal membrane and row of fine setules along inner margin. Endopod ( Figs. 2F View FIGURE 2 , 3D View FIGURE 3 ) 3-segmented; first segment bearing inner plumose seta; second segment elongate, armed with 2 inner plumose setae, and ornamented with rows of fine setules along outer edge; third segment smallest, with 6 distal plumose setae plus tuft of fine setules proximally on outer margin.

Leg 3 ( Figs. 4A View FIGURE 4 , 5A View FIGURE 5 ) biramous with rami separated by large gap; flattened apron-like sympod carrying extended strips of hyaline membrane along lateral and free posterior margins plus rows of spinules on outer surface and corrugated pad on mid-ventral surface ( Figs. 4A View FIGURE 4 , 5B View FIGURE 5 ); armed with inner coxal seta and outer basal seta positioned at base of exopod. Intercoxal sclerite narrow, with flap of hyaline membrane along posterior margin. Exopod 3- segmented: first segment with straight outer spine not reaching articulation between second and third segments, pecten-like strip of membrane present at base of outer spine; second segment with slender outer spine and inner plumose seta; third segment with 3 subequal outer spines and 4 short pinnate setae. Endopod 2-segmented; first segment extending laterally to form elongate velum closing off gap between bases of rami, segment armed with long inner pinnate seta; second endopodal segment bearing 6 pinnate setae and ornamented with row of long setules along outer margin.

Leg 4 ( Figs. 4B View FIGURE 4 , 5C View FIGURE 5 ) uniramous. Slender protopodal segment with outer distal seta. Exopod 2-segmented ( Figs. 4C View FIGURE 4 , 5C View FIGURE 5 ); first segment armed with slender outer distal spine ornamented with strips of membrane bilaterally; second segment with 1 lateral spine and 3 distal margin spines increasing in length from outer to inner, middle spine extending beyond middle of inner spine; inner and middle spines each with pecten at base. Spine (Roman numerals) and seta (Arabic numerals) formula of rami of legs 1–4 as follows:

Exopod Endopod

Leg 1 I-0; III,1,3 vestigial

Leg 2 I-1; I-1; II,I,5 0–1; 0–2; 6

Leg 3 I-0; I-1; III,4 0–1; 6

Leg 4 I-0; I, III absent

Leg 5 ( Fig. 4D View FIGURE 4 ) located ventrally near posterolateral corners of genital complex and represented by 2 papillae; outer (protopodal) papilla bearing single plumose seta; inner (exopodal) papilla carrying 2 equal plumose setae: seta on outer papilla longest.

Adult male ( Fig. 6A View FIGURE 6 ) Total body length 1.93–2.08 mm (n = 2); dorsal cephalothoracic shield slender, longer than wide (1.05–1.10 × 0.70–0.72 mm) excluding hyaline membranes, narrowing anteriorly and with broad marginal membranes on lateral zones. Thoracic zone of shield slightly wider than long (0.57‒0.58 × 0.59‒0.60 mm) and comprising about 54% of cephalothorax length. Fourth pedigerous somite short, much wider than long (0.05–0.06 × 0.23–0.24 mm) and distinctly separated from cephalothorax and genital complex. Genital complex elongate, longer than wide (0.40–0.43 × 0.26–0.27 mm), lateral margins indented anteriorly, with slightly convex lateral margins and straight posterior edge, about 38% of cephalothorax length. Abdomen 2-segmented; first free abdominal somite subrectangular, about 1.4 times wider than long (0.14‒0.17 × 0.20‒0.24 mm), anterior part slightly wider than posterior part; anal somite longer than wide (0.22–0.27 × 0.14–0.17 mm) and about 1.57 times longer than preceding abdominal somite: combined length of genital complex and entire abdomen about 72% of length of cephalothorax. Caudal rami slightly longer than wide (0.10–0.13 × 0.06–0.08 mm), about 45% of anal somite length, carrying 6 plumose setae.

Antennule as in female. Antenna ( Figs. 6B,C View FIGURE 6 , 7A View FIGURE 7 ) 3-segmented; proximal segment elongate, with corrugated adhesion pad distally on ventral surface; middle segment largest with corrugated pads on medial and distal surfaces ( Figs. 6C View FIGURE 6 , 7A View FIGURE 7 ) (SV-IZM3); posteriorly-directed distal segment with 2 fused subrectangular and overlapping plates ( Figs. 6C View FIGURE 6 , 7A View FIGURE 7 ), first (upper) plate ornamented with slightly curved cuticular ridge ( Fig. 7A View FIGURE 7 arrow), second plate subrectangular and spatulate, armed with 2 slender basal setae. Postantennal process ( Fig. 6D View FIGURE 6 ) more curved than that of female and with tapering tine. Maxillule ( Fig. 6E View FIGURE 6 ) comprising tapering posterior dentiform process and anterior papilla bearing 3 subequal naked setae. Mandible and maxilla as in female. Maxilliped ( Figs. 6F View FIGURE 6 , 7B, C View FIGURE 7 ) with massive corpus produced into large conspicuous triangular process in myxal area plus small subtriangular process proximally ( Figs. 6G View FIGURE 6 , 7B, C View FIGURE 7 arrowheads) (SV-IZM4); distal surface of small myxal process covered with slight corrugations ( Fig. 6G View FIGURE 6 ). Subchela armed with 2 small sensilla plus another longer seta at base of claw ( Figs. 6F View FIGURE 6 , 7B View FIGURE 7 arrows). Sternal furca ( Figs. 6H View FIGURE 6 , 7C View FIGURE 7 ) with tines positioned immediately next to each other, tines about 1.3 times longer than tines of female.

Legs 1–4 as in female. Leg 5 ( Fig. 6I View FIGURE 6 ) represented by 2 papillae located on posterolateral margin of genital complex: outer papilla with 1 long plumose seta and inner (exopodal) papilla with 2 equal plumose setae. Leg 6 ( Fig. 6I View FIGURE 6 ) represented by single papilla on margin of genital operculum, bearing 2 equal pinnate setae.

Remarks

The new species, C. izmiriensis sp. nov., displays several distinctive character states, the most prominent of which is the unusual form of the sternal furca. In both sexes the tines of the sternal furca are well defined but closely adpressed to each other along their entire length. This form of sternal furca is unique within the genus, although a similar, highly modified form of furca was reported for Caligus bocki Heegaard, 1943 by Heegaard (1943) who described this species as having the tines of the furca fused to form a tapering median spine. Solely based on this character Heegaard (1943) proposed a new subgenus Subcaligus Heegaard 1943 to accommodate C. bocki . This subgenus, based on a single autapomorphy, has not gained acceptance and was not even mentioned by Dojiri & Ho (2013) in their phylogenetic analysis of caligid genera. In the related caligiform genus Dissonus Wilson, 1906 the sternal furca is modified as a short tapering median stylet in one species, D. manteri Kabata, 1966 , but in other congeneric species the furca is either lacking or has the typical structure with paired tines ( Boxshall et al. 2008). In Caligus , as in Dissonus , such a level of variation in sternal furca expression can be readily accommodated within the genus, and we treat the subgenus Subcaligus as a junior subjective synonym of Caligus . Caligus bocki lacks plumose setae on the posterior margin of the distal exopodal segment of leg 1 ( Heegaard 1943) and the absence of these setae led ( Boxshall & El-Rashidy 2009) to place C. bocki in the C. productus -group of species. The possession of 3 plumose setae on the posterior margin serves to distinguish C. izmiriensis sp. nov. from C. bocki .

Caligus izmiriensis sp. nov. shares the same unusual form of leg 1 as Metacaligus yucatanensis Suárez-Morales, Kim & Escamilla, 2012 and a second new species from Turkish coastal waters, which is described below as C. sarosensis sp. nov. Detailed comparison of the two new species and M. yucatanensis is given below in the Remarks section for C. sarosensis sp. nov. Another remarkable feature of C. izmiriensis sp. nov. is the presence of paired flaps on the posteroventral surface of the genital complex of the female. Their function appears to be to partially conceal and presumably protect the attached spermatophores which discharge their contents into the copulatory pores of the female. As far as we can ascertain, these flaps are unique to C. izmiriensis sp. nov. within the genus. Their absence from other caligid species that spend extended periods of time swimming free in the plankton away from the host (i.e. species included in the Caligus undulatus -group) suggests that they are not associated with a more planktonic life style.

The shape of the genital complex differs remarkably between the young female and the holotype female, and we infer that this difference indicates that the holotype has undergone a post-mating metamorphosis, which is common in female caligids (see Boxshall & Özak 2022). In C. izmiriensis sp. nov. this metamorphosis involves a marked change in the shape of the genital complex from having convex lateral margins with the maximum width about in the middle to becoming subrectangular with parallel lateral margins, plus the development of distinct lobes at the posterolateral corners. In the young female the posterolateral corners are slightly indented and the posterior margin is v-shaped.

Mating in caligid copepods has been observed to take place on the surface of the host ( Anstensrud 1992) but mating behavior is currently unknown for the members of the Caligus undulatus -group. However, the presence in the plankton of both young females carrying recently deposited spermatophores and adult females that are postmetamorphic, suggests that the metamorphosis may take place away from any host in these planktonic forms.