Cymbasoma pseudobidentatum, Suárez-Morales & Goruppi & de Olazabal & Tirelli, 2017

Suárez-Morales, Eduardo, Goruppi, Alenka, de Olazabal, Alessandra & Tirelli, Valentina, 2017, Monstrilloids (Crustacea: Copepoda) from the Mediterranean Sea (Northern Adriatic Sea), with a description of six new species, Journal of Natural History (J. Nat. Hist.) 51 (31 - 32), pp. 1795-1834 : 1805-1811

publication ID	https://doi.org/ 10.1080/00222933.2017.1359698
publication LSID	lsid:zoobank.org:pub:3D4B38E4-CCCD-4BD6-AC57-B59343A865F7
persistent identifier	https://treatment.plazi.org/id/68115F0D-B37A-FFE2-FE48-B35FFBB320C3
treatment provided by	Felipe
scientific name	Cymbasoma pseudobidentatum
status	sp. nov.

Treatment

Cymbasoma pseudobidentatum sp. nov.

( Figures 4 View Figure 4 (a – g), 5(a – i))

Material examined

Adult holotype female from LTER-C1 station, Gulf of Trieste, northern Adriatic Sea (45° 42 ʹ 2.99 ” N, 13°42 ʹ 36.00 ‘ E) ( Figure 1 View Figure 1 , Table 1), partially dissected, appendages mounted on slide in glycerine, sealed with Entellan ®. Date of collection: 26 August 2015 . Slide deposited in ECO-CHZ-000000 . Adult male allotype from station 2, harbour of Trieste (45°37 ʹ 4.08 ’ N, 13°46 ʹ 30.96 ” E) ( Figure 1 View Figure 1 ), date of collection: 12 May 2014 . Specimen mounted on semi-permanent slide (ECO-CHZ-009523) .

Description of adult female

Body moderately elongated, slender ( Figure 4 View Figure 4 (a, b)); total body length = 0.78 mm. Cephalothorax = 0.48 mm long, representing 61.6% of total body length. Midventral oral papilla located at 27.5% of cephalothorax length. Pair of relatively large eyes present, pigment cups well developed, separated by one eye diameter, weakly pigmented; ventral cup slightly larger than lateral cups ( Figure 4 View Figure 4 (a)). Cephalic area moderately produced, with flat ‘ forehead ’, frontal surface smooth, with pair of sensilla. Cephalic cuticular ornamentation reduced, including (1) pair of small, symmetrical nipple-like ventral processes on preoral area and (2) unguiform scars and nipple-like processes at each side of oral papilla ( Figure 4 View Figure 4 (b, d)).

Urosome consisting of fifth pedigerous somite, genital double-somite and anal somite, together representing 15% of total body length. Relative lengths of urosomites (fifth pedigerous, genital-double and free somites) as: 34: 44: 22 = 100, respectively. Fifth pedigerous somite with straight lateral margins ( Figure 4 View Figure 4 (e)), fifth legs inserted on distal 1/3 of somite. Genital double-somite moderately expanded medially, with widely rounded margins; ventral surface expanded ( Figure 4 View Figure 4 (f)). Postero-lateral margins with small subtriangular processes (arrowed in Figure 4 View Figure 4 (e)). Anal somite about half as long as genital doublesomite, ventrally produced ( Figure 4 View Figure 4 (f)). Caudal ramus subquadrate, 1.1-times longer than wide, armed with three subequally long, sparsely setulated caudal setae. Ovigerous spines paired, relatively long, representing 30% of total body length. Spines basally separated, slender, equally long, straight at their base and along shaft, both tapering distally.

Antennule length 0.2 mm, representing about 26% of total body length and 44% of cephalothorax length; antennule 4-segmented, suture between segments 3 and 4 absent ( Figure 4 View Figure 4 (c)). Relative length of distal antennulary segment: 42%. In terms of pattern described by Grygier and Ohtsuka (1995) for female monstrilloid antennulary armature, setae (Roman numerals) and spines (Arabic numerals), short spiniform element 1 present on first segment; elements on second segment: 2d1-2, 2v1-3, and IId; element 2v 1 remarkably long, longest of 2v-d group. Third segment with robust, long element 3, as long as elements of 2v group. Setal elements IIId and IIIv present. Segment 4 bearing elements 4d1,2, 4v1-3. Setae IVd, IVv, Vd and Vv present. Aesthetasc 4aes present, slender. Element 5 spiniform, strong. Subterminal elements b1-5 present, unbranched; apical elements 61 and 62 and 6aes present ( Figure 4 View Figure 4 (c)).

Incorporated first pedigerous somite and succeeding three free pedigerous somites each bearing a pair of biramous legs. Pedigerous somites 2 – 4, together accounting for 24% of total body length in dorsal view. Legs 1 – 4 slightly increasing in size posteriorly. Intercoxal sclerites of legs 1 – 4 subrectangular, with smooth surface, decreasing in size ( Figure 4 View Figure 4 (i)). Legs 1 – 4 articulating with large, rectangular coxa along oblique line; with outer basipodal seta; on leg 3, this seta about 3.5-times longer than in the other legs, biserially setulated. Endopods and exopods of legs 1 – 4 triarticulated. Ramal setae all biserially plumose except spiniform apical seta on exopodal segment 3, with inner margin naked ( Figure 4 View Figure 4 (j)). Armature formula of legs 1 – 4 as in previous species.

Fifth legs basally conjoined, distinctly bilobate, inner (endopodal) lobe conspicuous, unarmed, arising proximally, digitiform, reaching slightly beyond midlength of long outer lobe. Outer (exopodal) lobe elongated, slender, armed with two subequally long setae on distal position ( Figure 4 View Figure 4 (f, g)).

Description of adult male

Total body length: 0.74 mm. Cephalothorax 0.33 mm long, representing 44.8% of total body length ( Figure 5 View Figure 5 (a)). Midventral oral papilla moderately developed, located at 24% of

cephalothorax length. Cephalic region slightly protuberant bilaterally in dorsal view. Pair of dorsal ocelli present, weakly developed; pigment cups medium-sized. Ocelli separated by the length of slightly less than one eye diameter, faintly pigmented. Ventral cup larger than lateral cups. Pair of sensilla observed between antennulary bases. Forehead area as in female, i.e. produced with flat lightly striated surface ( Figure 5 View Figure 5 (b, c)). Ventral rounded protuberance between antennule bases, similar to that of the female ( Figure 5 View Figure 5 (c)). Perioral ornamentation as in female, with reduced nipple-like processes at both sides of oral papilla plus small preoral papilla-like elements (arrow in Figure 5 View Figure 5 (d)).

Urosome consisting of fifth pedigerous, genital (carrying genital complex), preanal and anal somites ( Figure 5 View Figure 5 (e – g)). Fifth pedigerous somite with smooth ventral and dorsal surfaces. Genital somite slightly shorter than fifth pedigerous somite. Genital complex of type II (Suárez- Morales and McKinnon 2014), represented by pair of divergent, digitiform genital lappets ( Figure 5 View Figure 5 (f)), these being slightly asymmetrical, right ramus slightly narrower than left in ventral view ( Figure 5 View Figure 5 (f)); lappets barely reaching to midlength of long anal somite. Pair of small medial thumb-like processes present at common basal joint of lappets, lappets surface smooth. Anal somite with weak constriction, moderately expanded ventrally, about 1.2-times as long as preanal somite in dorsal and lateral views, comprising 30% of urosome length; no suture visible on ventral or dorsal surfaces. Caudal rami subrectangular, approximately 1.3- times as long as wide, about as long as anal somite. Each ramus with three caudal setae.

Antennule length 0.22 mm. Antennules relatively long, representing 29% of total body length, and 66% of cephalothorax length ( Figure 5 View Figure 5 (a)); 5-segmented, segments 1 – 2 and 2 – 3 separated, segments 3 – 4 fused, as in female. Segment 5 located distal to geniculation ( Figure 5 View Figure 5 (b)). Setal element 1 on first segment slender, moderately long, reaching halfway along second segment. Antennulary elements 2v1-3, 2d1,2 and IId present on second segment, with elements of group 2v-d long. Setal elements IIId, IIIv and long element 3 present on third segment. Fourth segment with elements 4d1-2, 4v1 – 3, IVd and IVv; element 4v 1 longest of 4v-d group, as in female. Fifth segment with 5 unbranched ‘ b ’ -group setae (A – D in Figure 5 View Figure 5 (b)) (as in female). As for Huys et al. (2007) setal nomenclature of the distal segment, elements A – E and 1, 2, 4 present.

Incorporated first pedigerous somite and succeeding three pedigerous somites, each bearing well-developed biramous legs. Pedigerous somites 2 – 4, together accounting for 34% of total body length in dorsal view. Coxae of each pair unarmed, joined by intercoxal sclerite, which is slightly longer than wide and ornamented with small quadrate fields of spinules ( Figures 5 View Figure 5 (i, h)). Bases of legs 1 – 4 separated from coxae posteriorly by oblique articulation; with outer basal seta; on leg 3, this seta about 7-times longer, sparsely setulated ( Figure 5 View Figure 5 (i)). Endopods and exopods of legs 1 – 4 triarticulated. Outer spine on distal exopodal segment of legs 1 – 4 about 0.3-times as long as segment. Armature formula of legs as in female.

Type locality

Station LTER-C1 (45°42 ʹ 2.99 ” N, 13°42 ʹ 36.00 ” E) in the Gulf of Trieste , North Adriatic Sea ( Figure 1 View Figure 1 ) GoogleMaps .

Etymology

The species name makes reference to the close resemblance of this species with its Australian congener C. bidentatus by adding the prefix ‘pseudo’.

Remarks

This species of Cymbasoma can be distinguished from its congeners by a unique combination of the following features: (1) the presence of small posterodorsal subtriangular processes on the female genital double-somite; (2) a medial ventral cephalic protuberance; (3) fused antennulary segments 3 – 4 in both the male and the female; (4) female outer fifth leg lobe armed with two subequally long setae plus a small, slender innermost seta; (5) a ventrally expanded anal somite in both the male and the female; (6) male genital complex with a pair of distinctive medial thumb-like processes.

There are only two other known species of Cymbasoma with posterior processes on the female genital double-somite. One is the Australian C. bidentatum Suárez-Morales and McKinnon, 2016 , a species with which the new species shares other characters like the general body proportions, antennule relative length, an anteroventral process between the antennule bases. The new species and C. bidentatum clearly diverge in the armature of the fifth legs (i.e. two setae in the new species, three in C. bidentatum ), the shape of the genital double-somite (evenly rounded and with no ventral processes in the new species, with marginal notches and ventral processes in C. bidentatum ) and the antennule segmentation (segments 3 – 4 fused in the new species, unfused in C. bidentatum ) ( Suárez-Morales and McKinnon 2016, figs. 20 and 21). The other species with such a process on the genital double-somite is from Trieste, as described below. The processes on the genital double-somite are clearly different in these two species; wider, less pronounced and in a more lateral position in C. clauderazoulsi sp.nov. ( Figure 6 View Figure 6 (f, g)) than in C. pseudobidentatum sp.nov. ( Figure 4 View Figure 4 (e)).

Because of the very small, inconspicuous female fifth leg inner seta, C. bidentatum sp. nov. can be confused with other species bearing only two long setae on the fifth leg outer lobe; this is a condition found in only a few Cymbasoma ( Suárez-Morales and McKinnon, 2016) : C. agoense Sekiguchi, 1982 from Japan and the Australian C. tharawalorum Suárez- Morales and McKinnon, 2016, C. lourdesae Suárez-Morales and McKinnon, 2016 , C. dakini Suárez-Morales and McKinnon, 2016 and Cymbasoma sp. Suárez-Morales and McKinnon, 2016. A brief comparison is made here to distinguish the new species C. pseudobidentatum from this small group of species. It differs from C. agoense and C. tharawalorum in the body shape and proportions; in these two congeners, belonging to the agoense species complex, the cephalothorax is clearly short and robust and antennules are very short ( Sekiguchi 1982, figure 6A; Suárez-Morales and McKinnon 2016, figs. 56 and 65). The new species differs from C. lourdesae by the relative length of the fifth legs; in the new species they do not reach the insertion of the ovigerous spines ( Figure 4 View Figure 4 (f)), whereas they reach beyond this point in C. lourdesae ( Suárez-Morales and McKinnon 2016, fig. 25E). In C. lourdesae the antennule resembles that of the new species, including a complete fusion of segments 3 – 4, but in the Australian species the antennulary elements b 1-3 are branched ( Suárez-Morales and McKinnon 2016, figure 24C) vs unbranched in the new species ( Figure 4 View Figure 4 (c)). A frontal cephalic process is present in C. lourdesae ( Suárez-Morales and McKinnon 2016, figs. 24B, C) and is absent in the new species; in addition, the genital double-somite is strongly globose in C. lourdesae , with a conspicuous ventral projection ( Suárez-Morales and McKinnon 2016, fig. 24F), thus differing from the moderately rounded margins and weak ventral expansion observed in the same somite in the new species.

The new species differs from C. dakini in the following characters: (1) the genital double-somite has a distinctive anteroventral process in C. dakini ( Suárez-Morales and McKinnon 2016, figure 7D), which is absent in the new species ( Figure 4 View Figure 4 (f)), (2) the female antennule segments 3 – 4 are fused in the new species vs a complete suture in C. dakini ( Suárez-Morales and McKinnon 2016, fig. 7G). In addition, the preoral ornamentation differs in both species, with a heavy cuticular striation pattern and a striated frontal process in C. dakini ( Suárez-Morales and McKinnon 2016, figs. 7A, B) vs a weak ornamentation and a smooth frontal process in the new species ( Figure 4 View Figure 4 (d)).

The new species has affinities with Cymbasoma sp. from Australia ( Suárez-Morales & McKinnon 2016), including a similar structure of the female fifth leg, a moderately rounded genital double-somite and a ventral cephalic rounded process. These species differ in the body proportions; in Cymbasoma sp. the cephalothorax represents 66% of the total body length vs 61% in the new species. In Cymbasoma sp. the cephalic area has a reticulate fringe ( Suárez-Morales and McKinnon 2016, figures 70B, C) that is absent in the new species ( Figure 4 View Figure 4 (b, d)). The eye cups are smaller than the ventral cup and more separated in Cymbasoma sp. than in the new species, with cups having the same diameter as the ventral cup ( Figure 4 View Figure 4 (a)). The antennule length, segmentation and armature of the new species could not be compared with Cymbasoma sp. because the Australian specimen is incomplete ( Suárez-Morales and McKinnon 2016).

The male C. pseudobidentatum closely resembles C. tenue ( Isaac 1975) , known from England and the Mediterranean ( Suárez-Morales and Riccardi 1997; Suárez-Morales 2000c). These two species differ in subtle characters. In C. tenue the medial processes on the base of the genital lappets are clearly acute ( Suárez-Morales and Riccardi 1997, fig. 3F; Suárez-Morales 2000c, fig. 6E) and smaller than in the new species, in which these processes are apically rounded, thumb-like and relatively larger ( Figure 5 View Figure 5 (f)). The anal somite has a medial constriction in the new species, thus differing from C. tenue , lacking this character ( Suárez-Morales and Riccardi 1997, fig. 3E; Suárez-Morales 2000c, fig. 6F). In addition, the b-group setae on the outer margin of the last segment of the antennule are unbranched in the new species ( Figure 5 View Figure 5 (b)) and branched in C. tenue (Suárez- Morales and Riccardi 1997, fig. 2D; Suárez-Morales 2000c, fig. 6D).

The male and female of C. pseudobidentatum sp.nov. were linked as being conspecific, based on the several morphologic characters they share, as follows: (1) the anteriorly produced but apically flat forehead with a pair of sensilla on the same position and with a similar adjacent cuticular ornamentation; (2) the position of the oral papilla and the arrangement of the reduced perioral ornamentation; (3) the presence of an anteroventral rounded process in the preoral area; (4) the antennulary segmentation, with segments 3 – 4 fused; (5) very long antennulary elements 2v 1 and particularly element 4v 1 being the longest of group 4v-d; and (6) anal segment expanded ventrally. A similar set of characters was used to match the male and female of C. quintanarooense in the Caribbean Sea ( Suárez-Morales 2000a).