Cymbasoma norvegicum Suarez-Morales and Mercado-Salas 2023, sp. n.

Cymbasoma norvegicum Suárez-Morales and Mercado-Salas sp. n.

(Figures 1, 2)

Material examined

Holotype. One adult female (ZMH K-62093), partially dissected, semi-permanent slide mounted in glycerine, sealed with acrylic nail varnish; deposited in the Crustacea Collection of the Museum of Nature Hamburg, Zoology. Specimen damaged, with cephalothorax twisted from sampling. Norwegian Channel; Cruise IceAge 2, Sta. POS456-867 (61° 59.830̍N, 000°30.400̍E), collected 24 July 2013 by Saskia Brix.

Type locality

Norwegian Channel, northern coast of Norway (61°59.830̍N, 000°30.400̍E); epibenthic sledge trawled in mesopelagic waters (302.5 m).

Etymology

The species name makes reference to the type locality (Norwegian Sea). Name in genitive case. Gender is neuter to match that of the genus.

Diagnosis

Female Cymbasoma with slender cylindrical cephalothorax representing about 50% of total body length, forehead weakly produced, coarsely corrugate, antennules with segments 2–3 partially fused and 3–4 fused, first antennulary segment unarmed; anal somite long, more than half as long as genital double-somite, with deep constriction on outer margins. Fifth legs bilobed, exopodal lobe armed with three setae, outermost seta being shorter and thinner than remaining two; endopodal lobe slender, unarmed, almost reaching distal margin of exopodal lobe.

Description of adult female

Specimen damaged, with cephalothorax and urosome twisted, integument broken on lateral margins, some furcal setae broken off. Body shape and tagmosis as usual in female Cymbasoma (Suárez-Morales and McKinnon 2016). Total body length: 2.03 mm, measured from anterior end of cephalothorax to posterior margin of anal somite (Figure 1). Cephalothorax length = 1.09 mm, representing about 54% of total body length (Figure 1). Oral cone located 0.18 of way back along ventral surface of cephalothorax (Figure 1). Cephalic region anteriorly produced in dorsal view, forehead with pair of minute sensilla and protuberant field of corrugate cuticle between antennule bases, forehead ornamentation not extending onto dorsal or ventral surfaces (Figure 2 (a)). Lateral naupliar eyecups present, unpigmented, rounded in ventral view; medial cup slightly larger in diameter than lateral cups (Figure 2 (a)). Two large, ovoid nipple-like cuticular processes located ventrally between antennule bases and oral cone (nlp in Figure 1). Integumental nipple-like processes with adjacent field of transverse cuticular striae (Figure 1). Antennules relatively long, almost 40% of cephalothorax length and 19.5% of total body length. Antennular length of holotype 0.36 mm, length ratio of antennular segments, from proximal to distal, 12.3:20.0:14.1:53.7 (= 100). Antennules cylindrical, slender, indistinctly 4-segmented (S1–S 4 in Figure 2 (b)), segments 1–2 separated, segments 2–3 partially fused and segments 3–4 fused; intersegmental division 2–3 marked by partial suture and weak constriction. Antennules armed with 0, 0; 1, V; 2, I; 9, III, aes setae (Arabic numbers), spines (Roman numbers), and aesthetascs (aes), respectively (Figure 2 (b)). Distal antennular segment longest (more than half the total antennule length: 53.7%), with two empty sockets suggesting broken-off apical elements. In terms of Grygier and Ohtsuka̍s (1995) basic setal nomenclature for female monstrilloid copepod antennules, element 1 absent from first segment, second segment with usual armature including elements 2v1–3, 2d1,2, and IId; purported third with elements 3, IIIv, and IIId. Purported fourth segment armed with elements IVv,d 4 aes, 4v1–3, 4d2, Vm, Vv, Vd, 5, 61,and b1–3,5,6 (Figure 2 (b)) (elements 62, 6aes, and b4 missing). First pedigerous thoracic somite incorporated into cephalothorax; succeeding three free pedigerous somites each bearing pair of biramous swimming legs. Pedigerous somites 2–4 accounting for 33.5% of total body length). Endopodites and exopodites of swimming legs 1–4 triarticulated and with same armament pattern, except for leg 1 exopod which has one seta less on the last segment. Swimming legs 1–4 increasing in size posteriorly, with exopods longer than endopods (Figure 1).

Armature formula of swimming legs (Roman numerals = spines, Arabic numerals = setae) as follows:

[table omitted]

Coxae of legs 1–4 unarmed, legs medially joined by smooth subrectangular intercoxal sclerite about 1.3 times as long as broad, with anterior margin curved (white dots in Figure 1). Basis separated from coxae posteriorly by diagonal articulation. Basis of legs 1–4 with hair-like outer basipodal seta (bs, P1–P 4 in Figure 1), that on P3 relatively longer. Outer distal corner of first and third exopodal segments of swimming legs 1–4 each with short, spine-like seta. Spine on first and third exopodal segments relatively short, about 0.3 times as long as carrying segments. All natatory setae lightly and biserially plumose except for spiniform seta on outer distal corner of third exopodal segments of legs 1–4, this being lightly setulated along inner side, but with continuous row of small denticles along outer margin; this setal element slightly curved on leg 1 (Figure 2 (e)) and straight in legs 2–4 (P1–P 4 in Figure 1).

Fifth legs bilobed, arising ventrally from posterior margin of fifth pedigerous somite; exopodal lobe elongate, cylindrical, slender, slightly broadening distally, armed with three distal setae, one of them thinner and shorter than subequally long remaining two. Endopodal lobe slender, cylindrical, arising from proximal inner margin of exopodal lobe, almost reaching its distal margin. Endopodal lobe unarmed, smooth (Figure 2 (a,d)).

Urosome relatively short, consisting of fifth pedigerous somite, genital double-somite, one free abdominal (anal) somite, and furca (Figure 2 (d)). Urosome accounting for 16.4% of total body length. Genital double-somite representing slightly less than half (43.3%) of urosome length. Genital somite with transverse cuticular wrinkles on lateral margins and dorsal surface (Figure 2 (d)). Medial ventral surface of genital double-somite moderately swollen, bearing long, basally conjoined ovigerous spines (Figures 1 (a) and 2(d)). Ovigerous spines moderately long, about 30% of total body length, reaching beyond distal end of furcal setae (osp in Figure 1). Anal somite relatively long, bell-shaped, more than half as long as genital double-somite; somite with constriction (notch) on outer margins and weak suture (as in Figure 1). Ratio of lengths of fifth pedigerous somite, genital double-somite, and anal somite: 30.1:43.3:26.7 = 100. Furca short, subrectangular, 1.75 times as long as wide, moderately divergent, bearing three terminal strong and subequally long setae, as usual in genus (Figure 2 (f)). Furcal setation incomplete in holotype specimen, with one furcal seta broken off on right ramus, but leaving sockets from which to infer original setation; left ramus with setation complete (setae 1–3 in Figure 1).

Male

Unknown.

Host

Unknown.

Remarks

The new species from off Norway can be readily assigned to the genus Cymbasoma by virtue of the presence of one free somite between the genital double-somite and the furca and by its possession of only three furcal setae (Isaac 1975 as Thaumaleus; Suárez-Morales and McKinnon 2016).

Two of the most distinctive characters of C. norvegicum sp. nov. are: (1) a long anal somite, more than half the length of the preceding genital double-somite; and (2) anal somite with a notch or sharp constriction on both lateral margins (as in Figure 1). Several known species of the genus share both characters: a long anal somite is found in females of several Cymbasoma species described by Suárez-Morales and McKinnon (2016) from Australia, such as C. annulocolle, C. colefaxi, C. constrictum, C. dakini, C. lourdesae and C. solanderi, and also C. davisi Suárez-Morales and Pilz, 2008 from Florida, C. striifrons Chang, 2012 from Korea, and C. rigidum (Thompson, 1888), C. thompsoni Giesbrecht, 1893, and C. germanicum (Timm, 1893) from Europe. Only a few also possess a notched, incompletely fused anal somite: C. paraconstrictum, C. rafaelmartinezi, C. fergusoni, C. lenticula and C. constrictum, from Australia (Suárez-Morales and McKinnon 2016), and also C. davisi Suárez-Morales and Pilz, 2008 from Florida, C. germanicum (Timm, 1893) from Helgoland (see Suárez-Morales 2006), C. rigidum (Thompson, 1888) from Canary Islands, and C. gigas A. Scott, 1909 from Indonesia. An additional sorting character is the presence of a bilobed fifth leg armed with three setae with an elongate inner lobe almost as long as the outer lobe. This character is shared with only four of all its known congeneric species: C. constrictum Suárez-Morales and McKinnon, 2016 from Australia, C. rigidum (Thompson, 1888) from Canary Islands, C. thompsoni Giesbrecht, 1893 from the Mediterranean, and C. germanicum (Timm, 1893) from Helgoland. The new species differs from these four species in several respects: in all these congeners, the female antennules are distinctly 4-segmented; no fusion of antennule segments has been reported in these other species (see Thompson 1888; Giesbrecht 1893; Suárez-Morales 2006; Suárez-Morales and McKinnon 2016). Furthermore, the new species C. norvegicum sp. nov. has an unarmed first antennulary segment; no other known species of Cymbasoma lacks antennulary setal element 1 (sensu Grygier and Ohtsuka 1995). This element may be much reduced like in C. bowmani, C. boxshalli and C. davisi (Suárez-Morales 1994; Suárez-Morales and Gasca 1998; Suárez-Morales and Pilz 2008), but its absence is an important character of the new species C. norvegicum. In Suárez-Morales̍ (2006) redescription of C. germanicum the complete antennule setation was confirmed. Also, the new species differs from C. germanicum in the absence of a lateral process on the genital double-somite (see Suárez-Morales 2006, fig. 2b). In C. constrictum the fifth leg inner lobe is distinctly shaped and clearly shorter than in C. norvegicum sp. nov. (Suárez-Morales and McKinnon 2016). In the known species of Cymbasoma related to C. rigidum, the fifth leg exopod innermost seta is distinctly shorter and thinner than the other two (see Suárez-Morales 2006), but the pattern is opposite in C. norvegicum sp. nov. (Figure 2 (c,d)).

Overall, the new species appears to be a member of the C. rigidum species group, probably comprising several undescribed species in different geographic areas, like the Mediterranean (Suárez-Morales 2011; Suárez-Morales and Grygier 2021), the western Caribbean (Suárez-Morales et al. 2020b), northern Europe, and now the North Atlantic as well. Based on morphological comparisons among different types of fifth legs historically attributed to C. rigidum, Suárez-Morales (2006) noted several morphological differences among previous reports of this species from distinct geographic regions. Cymbasoma norvegicum sp. nov. most closely resembles other members of the C. rigidum group, such as M. germanicum from the North Atlantic (Helgoland, Doggerbank (see Suárez-Morales 2006). The new species, here assigned as a new member of the C. rigidum species group, joins C. germanicum, several Australian species (ie C. constrictum, C. paraconstrictum, C. rafaelmartinezi, C. annulocolle) (Suárez-Morales and McKinnon 2016), and an undetermined number of species (at least 3–5) in other regions like the Black Sea–Mediterranean (Suárez-Morales and Grygier 2021) as members of the C. rigidum species group (Suárez-Morales 2006, 2011). The original description of C. rigidum by Thompson (1888) from off Tenerife is too vague to reliably determine the specific characters, and Thompson̍s drawings provide little information; hence, the species should be redescribed to assist in advancing the discovery of the diversity within this nominal species. It is expected that additional taxonomic work on this group will reveal many species, as has been recognised for another monstrilloid species group, C. longispinosum, currently comprising eight species from different geographic areas (Üstün et al. 2014; Suárez-Morales et al. 2020a, 2020b). Except for some specimens under study from the Gulf of California (Suárez-Morales pers. obs.), there are no previous reports on epi-mesopelagic monstrilloid copepods; new biological surveys in deeper benthic strata including plankton samplings are expected to reveal more species of this interesting group of copepods.