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

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

(Figures 3, 4)

Material examined

Holotype. One adult female (ZMH K-62094), partially dissected, semi-permanent slide mounted on glycerine, sealed with acrylic nail varnish; deposited in the Crustacea Collection of the Museum of Nature Hamburg, Zoology. Specimen with cephalothorax partially twisted and both antennules broken off from sampling or previous manipulation and preservation. Material collected off the coast of north-west Iceland; Cruise IceAge 1, Station M 85/3-1104 (66°38.600̍N, 024°31.970̍W), collected 13 September 2011 by Saskia Brix.

Type locality

North-west Iceland (66°38.600̍N, 024°31.970̍W). Epibenthic sledge trawled at a depth of 118.8 m.

Etymology

The species name is dedicated to our colleague and friend Prof. Dr Pedro Martinez Arbizu (Senckenberg Research Institute) for his relevant contributions to the systematics of the Copepoda. Name in genitive case; the gender is masculine.

Diagnosis

Cymbasoma with robust, medially expanded cephalothorax, forehead anteriorly produced into subtriangular swelling, with wrinkled surface, antennules absent in holotype except for first segment; genital somite with conspicuous rounded protuberances on posterolateral margins; anal somite more than half as long as genital double-somite, with deep constriction on outer margins. Fifth leg bilobed, endopodal and exopodal lobes fused, forming thick cylindrical ramus armed with three subequally long setae; inner protuberance representing endopodal lobe unarmed, located close to distal margin of fifth leg ramus.

Description of adult female

Body shape and tagmosis as usual in female Cymbasoma (Suárez-Morales and McKinnon 2016). Total body length of holotype individual = 2.07 mm, measured from anterior end of cephalothorax to posterior margin of anal somite. Cephalothorax length = 1.02 mm, representing about 49% of total body length (Figure 3). Oral cone located 0.18 of way back along ventral surface of cephalothorax (oc in Figure 3). Cephalic region tapering on anterior 1/5, forehead anteriorly produced into medial subtriangular swelling ornamented with irregular pattern of cuticular wrinkles. Middle section of cephalothorax expanded, with rounded margins (Figures 3 and 4 (a)). Naupliar eyecups present, two lateral cups larger than medial cup, unpigmented, rounded in dorsal view. Forehead swelling with confluent pattern of cuticular striations (fh in Figure 4 (a)). Two large, rounded nipple-like integumental processes (nlp in Figure 3) located ventrally between antennule bases and oral cone. Paired nipple-like integumental processes large, with adjacent field of transverse striae (str in Figure 3). Antennules absent, broken off during collection and handling, only first segment left, but short, slender element 1 (sensu Grygier and Ohtsuka 1995) is still present (* in Figure 3). Structure of legs 1–4, including armature formula, as in C. norvegicum sp. nov. Basipodal seta of leg 3 not noticeably longer than that of other legs (bs in Figure 3).

Coxae of legs 1–4 smooth, joined by smooth subrectangular intercoxal sclerite about 1.3 times as long as broad (white dots in Figure 3).

Fifth legs each with single ramus, proximally separate, fifth leg rami arising ventrally from distal part of fifth pedigerous somite; outer (exopodal) lobe subrectangular, robust, broad, armed with two distal and one subdistal setae, subequal in length and breadth (Figure 4 (d,e)). Inner (endopodal) lobe almost entirely fused to exopodal ramus, observable as an inner protuberance of the exopodal ramus, not reaching its distal margin. Endopodal lobe unarmed, smooth (enp in Figure 4 (e)).

Urosome relatively short, consisting of fifth pedigerous somite, genital double-somite, one free abdominal (anal) somite, and furca. Urosome accounting for 18.4% of total body length. Genital double-somite representing slightly less than half (45.2%) of urosome length (Figure 4 (c)). Genital somite roughly cylindrical, with proximal half bilaterally expanded, rounded. Somite with cuticular wrinkles on lateral margins (Figure 4 (b)) and with conspicuous rounded protuberances on posterolateral corners of somite (gs in Figure 3), processes laterally (arrow in Figure 4 (d)) and dorsally (arrows in Figure 4 (d)) visible. Medial ventral surface of genital double-somite moderately swollen, bearing long, basally conjoined ovigerous spines (osp in Figure 3 and Figure 4 (b,d)). Ovigerous spines relatively long, about 34% of total body length, reaching beyond distal end of furcal setae. Anal somite (as in Figure 3 slightly less than half (45.2%) as the length of genital double-somite, bell-shaped, with strong outer constriction (notch) and weak suture visible laterally on outer margins (st in Figure 4 (b)). Ratio of lengths of fifth pedigerous somite, genital double-somite and anal somite: 26.1:45.2:28.7 = 100. Furca subrectangular, 1.4 times as long as wide, moderately divergent, bearing three strong and subequally long terminal setae, as usual in genus. Furcal setation incomplete in holotype specimen, with two furcal seta broken off on right ramus, but leaving two sockets from which to infer original setation; left ramus with setation complete (1–3 in Figure 3).

Male

Unknown.

Remarks

Despite its damaged parts, likely resulting from the sampling method, the holotype specimen was still in reasonably good condition for taxonomic study. The absence of both antennules in the holotype specimen was not an obstacle in assigning it to the genus Cymbasoma as it clearly shows the characters recognised by Suárez-Morales and McKinnon (2016) as distinctive of the genus, including the presence of only one free somite between the female genital double-somite, and the armature of the furca consisting of only three furcal setae (Isaac 1975; Suárez-Morales and McKinnon 2016). The new species can be easily recognised by several characters: (1) an anteriorly produced subtriangular forehead furnished with cuticular wrinkles; (2) fifth leg with outer and inner lobes almost completely fused, forming a thick lobe armed with three distal setae and with reduced endopodal lobe; (3) presence of rounded processes on the posterolateral margin of the genital double-somite; and (4) anal somite with deep notch and suture. This combination of characters is unique and has not been observed in any other species of Cymbasoma. An anteriorly produced forehead is rare among species of Cymbasoma; it is known in the Australian C. buckleyi Suárez-Morales and McKinnon, 2016 and also, with weaker expressions, in the Caribbean C. bowmani Suárez-Morales and Gasca, 1998 and C. alvaroi Suárez-Morales, Carrillo and Morales-Ramírez, 2013, and in C. concepcionae Suárez-Morales and Morales-Ramírez, 2003 from the Eastern Tropical Pacific. The new species differs from C. buckleyi in the shape of the genital double-somite (strongly globose in C. buckleyi) and in the shape and structure of the fifth legs, with a distinct inner lobe (Suárez-Morales and McKinnon 2016, fig. 42E); in both C. bowmani and C. concepcionae the fifth leg is uniramous and the anal somite is unmodified (Suárez-Morales and Gasca 1998; Suárez-Morales and Morales-Ramírez 2003), thus diverging from the new species, whereas in C. alvaroi the forehead is unornamented, the anal somite is unmodified, and the fifth leg has a short, distinct inner lobe (Suárez-Morales et al. 2013, fig. 6E).

The new species C. pedroi is assignable to the C. rigidum species group. Completely fused outer and inner fifth leg lobes have been reported in two species related to C. rigidum, as in the illustrated records of C. rigidum from Scotland by Scott (1904) and by Bernier et al. (2002) from Canada. A genital double-somite with posterolateral protuberances has been reported in C. lenticula and C. astrolabe Suárez-Morales and McKinnon, 2016, both from Australia. Cymbasoma pedroi sp. nov. differs from these two species in the fifth leg structure; also, in both Australian species the inner lobe is clearly separated from the outer lobe (Suárez-Morales and McKinnon 2016, figs. 44E, 39A).

The new species C. pedroi sp. nov. shows several affinities with members of the C. rigidum species group. The main defining characters of the group are based on descriptions and illustrations by Thompson (1888), Bourne (1890), Scott (1904), Sars (1921), and Suárez-Morales (2006), including: (1) anal somite with constricted lateral margins and about half the length of the genital double-somite; (2) fifth leg with exopodal lobe carrying three setae, endopodal lobe partly fused, as in Bernier et al.̍s (2002) record of C. rigidum from Canada and in C. pedroi sp. nov., or separate, as in C. norvegicum sp. nov. and Bourne̍s (1890) record from England; (3) cephalothorax representing about 50% of total body length; (4) ovigerous spines reaching beyond distal end of furcal setae; and (5) genital double-somite with laterally expanded proximal half, with posterolateral rounded processes (viz Suárez-Morales 2006, fig. 4b,d; Suárez-Morales and McKinnon 2016, fig. 44F), as in C. germanicum and C. astrolabe, also members of the group. Overall, it is clear to us that the new species C. pedroi sp. nov. can be taxonomically recognised by the characters mentioned, but represents, together with C. norvegicum sp. nov., the only epi-mesopelagic members of the C. rigidum species group. The two new species described herein show some genera resemblances, such as the proportions of the urosomites and the general body shape, but also poorly developed eyes, equally long ovigerous spines,and equally long basipodal setae of legs 1–4; however, they differ in several respects, including: (1) the development of the fifth leg endopodal lobe, which is fused, reduced in C. pedroi and unfused, well developed in C. norvegicum; (2) an anteriorly produced subtriangular forehead in C. pedroi vs a flat, corrugate forehead in C. norvegicum; (3) antennule lacking setal element 1 on first segment in C. norvegicum vs element 1 present in C. pedroi; (4) C. pedroi has distinctive rounded protuberances on posterolateral margins of the genital double-somite vs such processes lacking in C. norvegicum.

The occurrence of these planktonic female monstrilloids representing two new species from epi-mesopelagic depths suggests that deeper waters could harbour an unknown diversity of monstrilloids that certainly deserves further investigation. Epibenthic sledges have been reported as efficient gear with which to sample epibenthic copepods (Brandt et al. 2014) and, in the case of the planktonic adult monstrilloids, with limited swimming capacity, specimens are likely to be obtained close to their potential hosts just within or above the epibenthic stratum; the endoparasitic juveniles would be collected together with the parasitised Polychaeta hosts. The sampling method arguably explains the damage observed in our type specimens.

Molecular diversity. In order to provide a more robust description of the new species, DNA extractions and amplifications of the nuclear large (28S) and small (18S) subunits of the rRNA and of the mitochondrial protein cytochrome c oxidase subunit I (COI) were carried out. From both species, sequences of the 28S and the 18S subunits were successfully produced (accession numbers in Table 2). In the case of 18S, we targeted to amplify 1792 bp by using internal primers; however, we were able to retrieve only 1024 bp for C. norvegicum and 1023 bp for C. pedroi, with 1016 bp identical sites and 100% similarity between species. For the 28S subunit, sequences of 806 bp were produced for C. norvegicum and 780 bp for C. pedroi; these had 757 bp identical sites and 100% similarity between species. Unfortunately, we were not able to produce COI sequences despite testing a variety of primer pairs and PCR protocols.