Canuellina pacifica, Gómez & Yáñez-Rivera & García-Vázquez & Armenteros, 2024

Gómez, Samuel, Yáñez-Rivera, Beatriz, García-Vázquez, Leonardo & Armenteros, Maickel, 2024, On some new species of Canuelloida Khodami, Vaun MacArthur, Blanco-Bercial & Martinez Arbizu, 2017 (Crustacea: Copepoda) from a shallow coastal lagoon in north-western Mexico, Zootaxa 5555 (4), pp. 497-534 : 530-531

The genus Canuellina and justification of C. pacifica sp. nov.

Sewell (1940) proposed Ellucana as a new subgenus of Canuella Scott T. & Scott A., 1893 for Canuella (Ellucana) longicauda Sewell, 1940 found in weed-washings at Nicobar Island. Coull (1971) gave the subgenus Ellucana full genus rank, and described E. secunda from the North Carolina continental shelf. Additionally, he commented on the presence of this species in Barbados ( Coull 1970). Coull (1971) believed that Ellucana and Canuellina were closely related by the reduction in setation of P2 and P3, and by the similar genital fields. Coull (1971) gave an ample list of differences between E. longicauda and E. secunda from which he separated both species, but probably driven by Sewell’s (1940) brief description of E. longicauda , he suspected that, if rediscovered, the latter would prove to be conspecific with E. secunda . In his redescription of E. longicauda, Fiers (1982) rediagnosed the genus Ellucana and commented on the similarity between that genus and Canuellina . Fiers (1984) partially redescribed the female of E. secunda found in washings of coarse coral sand from Curaçao, and despite his list of differences, he concluded that E. secunda and E. longicauda were closely related. In his brief diagnosis of Canuellina, Por (1984) gave a list of species of that genus in which he included, without any reasoning, Canuellina secunda . By 1984, E. secunda was known to be distributed in Barbados, North Carolina, and Curaçao ( Coull 1970, 1971; Fiers, 1984), and Yucatan, Mexico ( Fiers 1984). Huys (2016) detected two lineages amongst the species included in Ellucana and Canuellina and he transferred C. onchophora Por, 1967 and C. nicobaris Wells & Rao 1987 to Ellucana , and E. secunda to Canuellina . These moves were based on i) the presence of normal outer spines on P4EXP2 and EXP 3 in Ellucana , but elongated outer elements in Canuellina , ii) the shape of the male genital field with triangular opercula bearing a long basal styliform element and an inner uncinate spine, and a slender apical seta in Ellucana , but with several chitinized areas and lack of triangular opercula in Canuellina , and iii) male P4EXP3 sexually dimorphic in Ellucana , but P4EXP3 not modified in the males of Canuellina ( Huys 2016) . The male genital field is very similar in a core of species of Canuellina , viz. C. canalis , C. femur , and C. tuba (the male of C. insignis remains unknown). The opercula in C. canalis , C. femur , and C. tuba is reduced to a small plate with a distal short seta, and the inner uncinate spine and the basal styliform element are larger than in Ellucana . The male genital field in C. secunda is radically different. It is composed of P6 bearing four setae (one inner minute, one middle inner long, one middle outer half as long as the previous seta, and one outer element).

The Mexican material is clearly related to C. secunda . It fits all previous descriptions of the latter, but some differences were detected. These are: i) P5-bearing somite with dorsal pattern of chitinized plates in the new species, absent in C. secunda , ii) female and male caudal ramus with seven setae of which six unmodified, and one transformed into triangular blunt, hyaline spiniform dorsal element close to outer subdistal margin, but caudal ramus with six unmodified setae in C. secunda , iii) antennary basis with one seta in the new species, but basis unarmed in C. secunda , iv) relative length of the distal inner seta on the P3EXP3 (nearly half as long as the distal outer seta in C. pacifica sp. nov., but distal inner seta only slightly shorter than the distal outer element in C. secunda , v) relative length of the distal inner element on P3ENP3 (shorter than distal outer seta in C. pacifica sp. nov., but visibly longer in C. secunda ), vi) relative length of the distal inner seta on P2EXP3 (visibly shorter than distal outer element in C. pacifica sp. nov., but as long as distal outer element in C. secunda ), vii) P2ENP2 with long stiff inner seta parallel to inner margin of outer projection in C. pacifica sp. nov., but ENP2 unarmed in C. secunda .

At present, the genus Canuellina is composed of C. canalis from the Suez Canal, Sirbonian lagoon and south Red Sea ( Por 1969), C. femur from the Gulf of Eilat ( Por 1967), C. insignis from Port Said (Suez Canal) ( Gurney 1927), C. tuba from the Gulf of Eilat and Red Sea ( Por 1983), and C. secunda known from the Gulf of Mexico and the Caribbean Sea ( Coull 1970, 1971; Fiers 1984), and C. pacifica sp. nov. from the Mexican eastern tropical Pacific (present study). We believe that Canuellina , as currently known, is composed of two different lineages. The canalis lineage ( C. canalis , C. femur , and C. tuba , and most probably, C. insignis ) is distributed in the Red Sea and Suez Canal areas. The Neotropical secunda lineage ( C. secunda and C. pacifica sp. nov.) is distributed in the Gulf of Mexico, Caribbean Sea, and north-western coast of Mexico. These lineages share the elongate outer spines on P4EXP2 and EXP3, but can be readily separated by the shape of the male P6 and genital field.