Paracyclops chiltoni (Thomson, 1882)

Mercado-Salas, Nancy & Suárez-Morales, Eduardo, 2009, A new species and illustrated records of Paracyclops Claus, 1893 (Copepoda: Cyclopoida: Cyclopinae) from Mexico, Journal of Natural History 43 (45 - 46), pp. 2789-2808 : 2801-2803

Paracyclops chiltoni (Thomson, 1882)

( Figures 6 , 7 )

Material examined

Two adult female specimens from a water reservoir in the lagoon of Silvituc (18°37′37.44′′ N, 90°16′44.12′′ W), state of Campeche, southeast Mexico, coll. Martha Gutiérrez-Aguirre, 13 October 1998. One specimen dissected, slide in collection of Zooplankton at ECOSUR-Chetumal (ECO-CHZ-02380). One undissected specimen in vial, ethanol-preserved (ECO-CHZ-02380) .

Remarks

The main morphological characters stated as diagnostic by Karaytug (1999) for this presumably cosmopolitan species are present in the Mexican specimens; these include: eight antennular segments ( Figure 6A ), genital double-somite about as long as broad, a relatively short outer seta of the fifth legs, which is as long as the inner spine or slightly longer, the absence of a cluster of spinules on the insertion of two coxobasal setae of the antennae in the female (which is present in the male), and cuticular depressions on the ventral surface of the caudal rami. The specimens from Campeche, Mexico, show some variation with respect to the description of P. chiltoni from New Zealand, the country from where this species was originally described. Our specimens exhibit differences in several characters, including the presence of only two cuticular pits on the ventral surface of the caudal rami ( Figure 6G ); according to Karaytug and Boxshall (1998b) and Karaytug (1999), this character is weaker or less defined in specimens from outside the Palaearctic region. In the Campeche material, the relative length of the outer seta of the fifth leg is distinctly longer than the inner spine ( Figure 7D ); according to Karaytug and Boxshall (1998b), this character was found only in some specimens from New Zealand, whereas in most other specimens both elements are equally long. The spinulation of the anal somite was most similar to the specimens from Brazil depicted by Karaytug and Boxshall (1998b), with a denser array of the longitudinal row of spinules on the anal cleft (see Figure 6F ), but with a shorter transverse row, covering only half of the insertion margin of the caudal rami. The caudal rami ( Figure 6F,G ) are relatively shorter in both the Mexican (length: width ratio = 3.1) and the New Zealand (2.9) specimens than in those from Brazil (3.5) (Karaytug 1999). As in the New Zealand specimens, the Campeche females have an innermost terminal caudal seta slightly longer than the posterolateral seta, but in our specimens it is 70% as long as caudal ramus versus 63% in the New Zealand females. In the specimens of P. chiltoni examined by Karaytug (1999), the diagonal dorsal row of spinules on the caudal rami continues ventrally and is observable in this position, but in the Mexican specimens, spinules are absent from the ventral surface ( Figure 6G ). Dorsally, this row is slightly curved anteriorly, as in the specimens from Brazil (see Karaytug and Boxshall 1998b). In leg 1 ( Figure 7B ) there is some variation in the ornamentation of the coxa and the basipod (i.e. distal row with longer and fewer elements in the Mexican specimens, denser cluster on the outer edge of coxa, row of spinules absent on insertion of exopod), but the main difference is in the heavier and denser spinulation of the outer margins of the endopod and exopod. The same is true for legs 2–4 ( Figures 6D,E , 7A,C ). The coxal ornamentation of leg 4 is similar to that of the New Zealand specimens, with two rows of small spinules versus strong, longer elements in the Brazilian specimens (see Karaytug 1999). The ornamentation of the antennal coxobasis is almost identical to that depicted by Karaytug and Boxshall (1998b), except for shorter semi-circular row on middle surface of segment, denser field of spinules on proximal outer surface and inner distal row of spinules ( Figure 6B,C ).

Overall, the morphological variations observed in the Mexican specimens from Campeche are within the range of variability of this species, as demonstrated by Karaytug and Boxshall (1998b) and Karaytug (1999); hence, they are clearly assignable to this species. This is the first illustrated record and morphological comparison of P. chiltoni from Mexico.

Figures

Figure 6. Paracyclops chiltoni, adult female from Campeche, Mexico. (A) Antennule; (B) antenna; (C) coxobasis of antenna, frontal view; (D) leg 4 with separated endopod and exopod; (E) coupler of leg 4; (F) urosome, dorsal view; (G) same, ventral view showing fifth legs. Scale bars A, D–G, 50 µm, B, C, 25 µm.

Figure 7. Paracyclops chiltoni, adult female from Campeche, Mexico. (A) Leg 2 with separated endopod and exopod; (B) leg 1 with separated endopod; (C) leg 3 with separated exopod; (D) fifth leg. Scale bars A–D, 50 µm.