Cymbasoma alvaroi Suárez-Morales and Carrillo, 2013

Suárez-Morales, Eduardo, Carrillo, Allan & Morales-Ramírez, Alvaro, 2013, Report on some monstrilloids (Crustacea: Copepoda) from a reef area off the Caribbean coast of Costa Rica, Central America with description of two new species, Journal of Natural History (J. Nat. Hist.) 47 (5 - 12), pp. 619-638 : 631-635

Cymbasoma alvaroi Suárez-Morales and Carrillo , sp. nov.

( Figures 6 , 7 )

Diagnosis

Medium-sized species (1.74 mm), oral papilla located 0.27 of the way back along cephalothorax, antennules short 18% of total body length. Forehead with medial rounded process between antennule bases. Inner seta of fifth legs shorter and thinner than the other two setae. Inner lobe of fifth legs not reaching half the length of outer lobe. Proximal half of genital double somite rounded, anal somite with ridged margins.

Material examined

Holotype. Adult female, partially dissected, ethanol-preserved, vial. Plankton collection, Cahuita National Park (sta. M3: 9 ◦ 44.30 ′ N, 82 ◦ 48.30 ′ W), Costa Rica. Date and hour of collection: 18 November 2010, 14:55 h. Some appendages on slides, mounted on glycerine, sealed with Entellan ®, ECO-CHZ-07569. Original zooplankton samples deposited at CIMAR, San José, Costa Rica.

Description

Total body length of female holotype: 1.74 mm, measured from anterior end of cephalic somite to posterior margin of anal somite. Cephalothorax incorporating first pedigerous somite narrow, relatively long, accounting for 61.7% of total body length ( Figure 6A,B ). Forehead rounded, strongly protuberant in dorsal view, anteriormost dorsal surface smooth. Two pairs of nipple-like cuticular processes on ventral surface between antennule bases and oral papilla; anterior pair with large, strong processes; posterior one with reduced structures. Processes surrounded and connected medially by field of weak transverse cuticular ridges not reaching base of oral papilla. Oral papilla protuberant, located close to anteriormost part of body, midventrally 0.27 of way back along cephalothorax ( Figure 6C ). Nauplius eye moderately developed; lateral cups relatively large, strongly pigmented at inner margins, eyes contiguous, medially conjoined. Ventral cup larger than lateral cups.

Antennule length 0.32 mm. Antennules relatively short, slightly shorter than 18% of total body length, and about 30% of length of cephalothorax. As usual in female monstrillids, antennules four-segmented, intersegmental divisions well-defined. Ratio of lengths of segments (proximal-distal): 20.6: 25.5: 12.1: 41.8 = 100. Following pattern described by Grygier and Ohtsuka (1995) for monstrilloid antennular armature, setae and spines on first (1), second (2d 1,2, 2v 1–3, IId), and third (3, IIIv, IIId) segments complete. Fourth segment with 4v 1,3, IVd, 4d 1, Vm, Vd, Vv, 5, 61, 62, 6aes, b 1–3, b 4,6. Setae b 1–3 unbranched ( Figure 7A ).

Incorporated first pedigerous somite and three free succeeding pedigerous somites, each bearing pair of biramous swimming legs. Intercoxal sclerite of legs 1–4 rectangular, naked. Lateral setae on basis of legs 1–4; basipodal seta on third leg longer and thicker than in the other swimming legs (2.5 times longer in leg 3 than in leg 1) ( Figure 7E ). Endopodites and exopodites of legs 1–4 triarticulated. Third exopodal segment with outermost terminal spiniform seta relatively short. Outer apical exopodal seta long, armed with small spinules along outer margin; inner margin with short setules arranged in tight pattern on legs 1–4 ( Figure 7C–F ). Armature of swimming legs shown in Table 3.

Fifth legs arising from medial base on fifth pediger. Each leg represented by outer main lobe and with small inner lobe. Outer lobe relatively wide distally, tapering toward base, elongated; ramus armed with three biserially setulated setae, two outer subequal in length and width, inner seta slightly shorter. Inner lobe digitiform, short, reaching about half the length of outer ramus ( Figure 6E ).

Urosome consisting of fifth pedigerous somite, genital double somite, and one free (anal) somite. Urosome, excluding caudal rami, accounting for 15.3% of total body length. Ratio of lengths of urosomites as (proximal–distal): 25: 50: 25 = 100. Second to fourth pedigers accounting for 23% of total length in dorsal view. Genital double somite with moderately expanded anterior half; posterior half with lateral margins straight; dorsal surface of genital double somite smooth ( Figure 7B ). Distal margin of somite with lateral half-moon-shaped cuticular process (arrowed in Figure 6D ). Genital double somite bearing relatively short (0.48 mm), basally separated ovigerous spines ( Figure 6E ), inserted ventrally on proximal half of double somite. Spines mostly slender along shaft, subequal in length, both weakly coiled at distal end ( Figure 6F ); spines representing about 42% of total body length, reaching well beyond distal end of caudal setae. Anal somite relatively long, with moderately divergent lateral margins ( Figure 6A ). Caudal rami subquadrate, about 1.1 times as long as wide, moderately divergent, bearing three setae ( Figures 6A , 7B ).

Male

Unknown.

Type locality

Cahuita National Park , Caribbean Coast of Costa Rica (9 ◦ 45 ′ N, 82 ◦ 49 ′ W) .

Etymology

The species is dedicated to Dr Alvaro Morales, a Costa Rican zooplankton researcher and active promoter of studies on marine Copepoda in Central America. This species is explicitly dedicated to him by the first authors and his name was omitted from the authorship of this taxon.

Remarks

The female monstrillid from Cahuita was easily assigned to the genus Cymbasoma by its possession of three caudal setae and the presence of three urosomites (fifth pedigerous, genital double, anal somite). Most of the known species of Cymbasoma have a fifth leg bearing an inner lobe, developed in different degrees; two main groups with this character have been defined within the genus, one related to Cymbasoma longispinosum ( Bourne, 1890) ( Grygier 1994b; Suárez-Morales and Escamilla 1997) and the other to Cymbasoma rigidum Thompson, 1888 (Suárez-Morales 2006). Only a reduced group of species have a fifth leg with a single lobe armed with three setae ( Suárez-Morales and Morales-Ramírez 2003, 2009). The first group, related to C. longispinosum , shares a relatively long cephalothorax, representing more than 55% of the total body length, a biramous fifth leg with a relatively reduced inner lobe, an outer lobe with three setae, and a well-developed genital double somite. Among these species, Cymbasoma morii Sekiguchi, 1982 (72%), Cymbasoma janetae Mageed, 2010 (71%), and Cymbasoma chelemense Suárez-Morales and Escamilla, 1997 (67%) have the longest cephalothorax. Other members of this group are C. longispinosum ( Bourne 1890; Giesbrecht 1893; Sars, 1921), Cymbasoma germanicum (Timm, 1893) (as redescribed by Suárez-Morales, 2006), Cymbasoma thompsoni ( Giesbrecht, 1893) , Cymbasoma gracile Gurney, 1927 , Cymbasoma californiense Suárez-Morales and Palomares, 1999 , Cymbasoma bali Desai and Krishnaswamy, 1962 , Cymbasoma tirmiziae Khan and Kamran, 1975 and Cymbasoma davisi Suárez-Morales and Pilz, 2008 .

The new species differs from these congeners in several characters. In C. californiense , C. chelemense , C. morii and C. thompsoni , the inner seta of the fifth leg is shorter and thinner than the other two setae; in the other species, including C. alvaroi sp. nov., the three setae are equally or subequally long and thick ( Grygier 1994b; Suárez-Morales and Escamilla 1997; Suárez-Morales and Palomares 1999). The genital double somite differs among these congeners; in the new species, C. alvaroi , the anterior half is rounded, slightly expanded, whereas it is subquadrate in C. californiense , C. chelemense , C. gracile , C. longispinosum and C. morii (see Giesbrecht 1893; Sars 1921; Grygier 1994b; Suárez-Morales and Escamilla 1997; Suárez-Morales and Palomares 1999). In C. janetae , C. morii , C. californiense , C. chelemense and C. longispinosum , the ovigerous spines arise from a fused basal shaft; in the other species, including C. alvaroi , the spines are separated at the base ( Bourne 1890; Grygier 1994b; Suárez-Morales and Escamilla 1997; Suárez-Morales and Palomares 1999; Mageed 2010). Overall, the new species appears to be most closely related to C. germanicum , redescribed by Suárez-Morales (2006) from Helgoland, and to C. davisi , from Florida ( Suárez-Morales and Pilz 2008). The general body proportions and the characters of the antennular armature, the genital double somite and the fifth legs are almost identical in the three species. They also share a distinctive lateral process on the distal margin of the genital double somite, a field of dorsal cuticular ridges on the same somite, and basally separated ovigerous spines (see Suárez-Morales et al. 2006; Suárez-Morales and Pilz 2008). There are several differences between these species: in C. alvaroi the relative length of the cephalothorax is 61% of the total body length, whereas both C. germanicum and C. davisi have a relatively shorter cephalothorax (57%). The three species have strongly developed nipple-like processes on the anterior surface of the cephalic area (Suárez-Morales 2006; Suárez-Morales and Pilz 2008), but in C. germanicum there is only a single pair of such processes and a second pair of weaker structures is present in C. alvaroi ( Figure 6C ) and in C. davisi . The new species has a rounded process on the forehead area between the antennule bases, a character absent in both C. germanicum and C. davisi . Also, the inner lobe of the fifth leg is differently developed in these species; in C. germanicum this lobe is long, slender, reaching the distal end of the outer lobe; in C. davisi it arises near the distal half of the segment and is cylindrical. In C. alvaroi this structure arises from the proximal half of the segment, it is shorter, barely reaching half the length of the outer lobe of the fifth leg, and it is slightly globose distally ( Figure 6E ). The cephalic ornamentation differs among these species: in C. davisi the anterior surface of the cephalic area is heavily covered with cuticular ridges from the eye level to well beyond the oral papilla, whereas this ridged field is restricted to the area of the nipple-like processes in both C. germanicum and C. alvaroi . Also, the cephalic area between the anterior and the oral papilla is concave in C. davisi and straight in the other two species. The position of the oral papilla is different in these species, 26.8% of the way back along cephalothorax in C. alvaroi versus 23% in C. davisi and C. germanicum . The anal somite has ridged margins in C. davisi and it is smooth in C. alvaroi and C. germanicum .

Figures

Figure 6. Cymbasoma alvaroi Suárez-Morales and Carrillo sp. nov., adult female from Cahuita, Costa Rica. (A) Habitus, dorsal; (B) habitus, lateral; (C) cephalic area, ventral, showing cuticular processes and ornamentation; (D) urosome, lateral, showing lateral process on distal margin of genital double somite; (E) fifth pedigerous and genital somites, ventral. Scale bars: A,B, 250 µm; C–E, 100 µm.

Figure 7. Cymbasoma alvaroi Suárez-Morales and Carrillo sp. nov., adult female from Cahuita, Costa Rica. (A) Right antennule, dorsal, showing armature following nomenclature by Grygier and Ohtsuka (1995); (B) urosome, dorsal, caudal setae cut short; (C) first swimming leg, dorsal; (D) second swimming leg, dorsal; (E) third swimming leg with longer basipodal seta, dorsal; (F) fourth swimming leg, dorsal. Most setae of swimming legs 1–4 cut short. Scale bars: A–F, 100 µm.