Cymbasoma specchii, 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 : 1801-1805

Cymbasoma specchii sp.nov.

( Figure 3 (a – h))

Material examined

Adult holotype female from station 4, located in the harbor of Trieste ( Figure 1 , Table 1), North Adriatic Sea, specimen partially dissected, appendages mounted on slide in glycerine, sealed with Entellan®. Date of collection: 15 July 2015. Slide deposited in ECO-CHZ-009522.

Description of adult female

Body moderately elongated, slender ( Figure 3 (a)); total body length = 1.31 mm. Cephalothorax 0.79 mm long, representing 60% of total body length. Midventral oral papilla

located at 26% of cephalothorax length. Pair of relatively large ocelli present, pigment cups well developed, medially conjoined, strongly pigmented; ventral cup slightly larger than lateral cups ( Figure 3 (a, c)). Cephalic area with slightly produced, rounded ‘ forehead ’, ornamented dorsally with simple transverse striations; ventral surface of forehead with shallow transverse striations and with pair of frontal sensilla ( Figure 3 (b)). Cephalic cuticular ornamentation including (1) pair of unguiform scars between bases of antennules, (2) pair of symmetrical nipple-like processes on anterior ventral surface in preoral area, with transverse adjacent striation, (3) small, medial pair of papilla-like processes, (4) striated ventral surface between nipple-like processes and oral papilla ( Figure 3 (c, d),)) and (5) shallow striation including distal half of cephalothorax ( Figure 3 (a, b)).

Urosome consisting of fifth pedigerous somite, genital double-somite and anal somite, together representing 17% of total body length. Relative lengths of urosomites (fifth pedigerous, genital-double and free somites) as: 25: 43: 32 = 100, respectively. Fifth pedigerous somite with medial constriction ( Figure 3 (f)), fifth legs inserted on distal 1/3 of somite. Genital double-somite with marginal cuticular ridges on lateral surfaces ( Figure 3 (f – h)) and shallow ventral striations anterior to insertion of ovigerous spines. Genital double-somite constricted, anterior half expanded, with rounded margins; posterior lateral margins produced into rounded processes (arrow in Figure 3 (h)). Anal somite about 74% as long as genital double-somite, medially constricted, with transverse lateral ridges. Caudal ramus subquadrate, 1.1-times longer than wide, armed with three subequally long, sparsely setulated caudal setae. Ovigerous spines paired, relatively short, 19% of total body length. Spines basally separated, relatively wide, robust, one slightly longer than the other, straight at their base and along shaft, both tapering distally.

Antennule length 0.27 mm, representing about 21% of total body length and 34% of cephalothorax length in the specimen examined; antennule 4-segmented, suture between segments 3 and 4 present ( Figure 3 (e)). 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), stout, short spiniform element 1 present on first segment; elements on second segment: 2d1-2, 2v1-3 and IId. Third segment with stout, long element 3, clearly longer than elements of the 2v group. Setal elements IIId and IIIv present. Segment 4 bearing elements 4d1,2, but elements 4v2,3 not observed; element 4v1 present. Setae IVd, IVv, Vd, and Vv present. Aesthetasc 4aes present, slender. Element 5 spiniform, short. Subterminal elements b1-4 present, unbranched; apical elements 61 and 62 and 6aes present ( Figure 3 (e)).

Incorporated first pedigerous somite and succeeding three free pedigerous somites each bearing a pair of biramous legs. Pedigerous somites 2 – 4, together accounting for 21% of total body length in dorsal view. Legs 1 – 4 slightly increasing in size posteriorly. Intercoxal sclerites of legs 1 – 4 subrectangular, smooth. Legs 1 – 4 articulating with large, rectangular coxa along oblique line; with outer basipodal seta; on leg 3, this seta is about 3.5-times longer than in the other legs, biserially setulated from proximal 1/3 and slightly thicker than those on the other legs. Endopods and exopods of legs 1 – 4 triarticulated. Ramal setae all biserially plumose except spiniform outer seta on exopodal segments 1 and 3, and inner seta of first exopodal segment, these latter being short, slender, and sparsely setulated. Also, outermost apical exopodal setae of legs 1 – 4 with inner margin ornamented with short setules, outer margin spinulose.

Armature formula of legs 1 – 4:

basis endopod exopod

leg 1 1 – 0 0 – 1;0 – 1;1,2,2 I-1;0 – 1;I,2,2

legs 2 – 4 1 – 0 0 – 1;0 – 1;1,2,2 I-1;0 – 1;I,1,2,2

Fifth legs basally separate, distinctly bilobate, inner (endopodal) lobe conspicuous, unarmed, arising proximally, reaching slightly beyond midlength of long outer lobe. Outer (exopodal) lobe elongated, slender, armed with three subequally long setae on distal position, innermost slightly longer than adjacent setae ( Figure 3 (f, g)).

Male. unknown.

Type locality

Harbour of Trieste , northern Adriatic Sea (45°37 ʹ 47.22 ” N, 13°46 ʹ 10.98 ” E) ( Figure 1 ) .

Etymology

The species name is warmly dedicated to Professor Mario Specchi who was Professor of Zoology at the University of Trieste; he inspired generations of marine biology students. As a marine ecologist he always stressed the importance of zooplankton research, carrying out studies ranging from taxonomy to fishery ecology.

Remarks

This female monstrillid from Trieste also belongs to the C. rigidum species complex by its possession of three subequal setae on the fifth leg and a well-defined fifth leg inner lobe, among other characters ( Suárez-Morales 2006). As described for the previous species, this fifth leg structure and ornamentation pattern resembles some records of C. rigidum , but some comments should be added first about this nominal species before comparing it further with the specimen from Trieste. The incomplete original description of C. rigidum by Thompson (1888) from the Canary Islands has represented an obstacle to morphologically define the true C. rigidum . Among the discernible characters of the original description, the large, unconstricted anal somite, representing about 70% of the genital double-somite length ( Thompson 1888, figs. 1 and 4), the unconstricted genital double-somite with weakly expanded anterior half, the strongly pigmented inner half of the medially conjoined lateral eye cups, and the relatively short antennulary element 3, allow some comparison. The structure of the fifth legs was incompletely described by Thompson (1888), but Bourne (1890) stated that his specimens from Plymouth are identical to those from the Canary Islands and added that they have ‘ ... relatively long endopodites ’; thus, he illustrated the Plymouth specimens as having a well-defined fifth leg inner lobe and three equally long setae on the outer lobe ( Bourne, 1890). So, a relatively large, unconstricted anal somite is an additional character related to the true C. rigidum . This strict pattern diverges in one or more characters from the reports assigned to this species by Scott (1904), Sars (1921), Wilson (1932) and Bernier et al. (2002), which should be revised (see Suárez-Morales 2006).

This new species from Trieste, C. specchii , has affinities with C. rigidum , with a clearly defined inner lobe reaching about halfway of the inner margin of outer lobe and three subequally long setae. It has also a long anal somite, representing 74% of the genital double-somite length. The new species differs from the strict C. rigidum pattern in the following characters: (1) the anal somite has a medial constriction; (2) the genital double-somite is also constricted and has posterolateral processes; (3) the antennulary element 3 is noticeably long ( Figure 3 (e)); (4) the fifth leg inner lobe does not reach the distal margin of the outer lobe (as in Bourne 1890, fig. 12). The Australian species C. constrictum Suárez-Morales and McKinnon, 2016 closely resembles the new species; both share a fifth leg with subequally long setae, a well-defined fifth leg inner lobe reaching about halfway of the outer lobe, a long, constricted anal somite, a similar genital doublesomite with posterolateral processes and a similar arrangement of cephalic ventral structures (i.e. nipple-like and papilla-like structures) ( Suárez-Morales and McKinnon 2016). They differ in several characters: (1) the body is clearly more robust and compact in C. constrictum ( Suárez-Morales and McKinnon 2016, fig. 37E) than in the new species; (2) the anal somite is as long as the preceding genital double-somite in the Australian species ( Suárez-Morales and McKinnon 2016, fig. 37E) vs a shorter anal somite in the female from Trieste (73% of genital double-somite) ( Figure 3 (h)); (3) the fifth pedigerous somite is expanded and ornamented with posterior ridges in C. constrictum , whereas it is constricted and with a smooth dorsal surface in the new species; (4) the antennule segments 3 – 4 are separate in the new species and fused in C. constrictum ; also, the antennulary element 3 is relatively longer in the new species ( Figure 3 (e)) than in C. constrictum ( Suárez-Morales and McKinnon 2016, fig. 37B); (5) the cuticular ventral ornamentation is weak in C. constrictum ( Suárez-Morales and McKinnon 2016, figure 37A) when compared with the striation pattern covering the anterior half of the cephalothorax in the new species ( Figure 3 (c, d)). Another Australian species with a long, constricted anal and genital compound somites and a similar fifth leg structure and ornamentation is C. paraconstrictum ( Suárez-Morales and McKinnon 2016) , but it can be distinguished by the presence of a dorsal protuberance that is absent from most other species of the genus; it also has a remarkably short distal antennulary segment, representing 35% of the appendage length vs 43% in the new species; the fifth leg inner lobe is long, reaching the distal margin of the outer lobe, thus diverging from the condition observed in the new species from Trieste.

Figures

Figure 1. Location of zooplankton sampling stations in the Gulf of Trieste (Italy), where monstrilloid copepods were obtained during the surveyed period.

Figure 3. Cymbasoma specchii sp. nov., holotype adult female from Trieste. (a) habitus, dorsal view; (b) same, lateral view; (c) cephalic region, ventral view; (d) same, preoral ventral surface an oral papilla, lateral view; (e) antennule with armature, dorsal view; (f) urosome with fifth leg, lateral view; (g) same, ventral view; (h) same, dorsal view showing posterolateral expansion on genital doublesomite. Scale bars: 200 µm (a, b), 50 µm (c, d), 100 µm (e–h).