Oncaea venusta Philippi 1843

Oncaea venusta Philippi, 1843

Figures 2–5

Synonymy (Medellín-Mora and Navas 2010: 302): Antaria coerulescens Claus, 1866; Antaria gracilis Dana, 1849; Oncäa venusta Giesbrecht, 1892; Oncaea obtusa Brady, 1883; Oncaea praeclara Humes, 1988; Oncaea pyriformis Lubbock, 1860

Material examined. Fifteen adult females undissected, 2 dissected (UARC 284M).

Remarks. The specimen from Colombia bears the diagnostic features of O. venusta as reported by Böttger- Schnack (2001) and Böttger-Schnack and Huys (2004). The body is cyclopiform, robust, habitus as in Figure 2. Body length, excluding caudal setae = 940–965µm, average: 0.95 µm (n = 15). Colombian specimens are characterized by 1) prosome tapering posteriorly, with small dorsal swelling on the P2-bearing somite (Fig. 2), 2) P6 with 4 pores on surface of genital double-somite (arrowed, Fig. 3), 3) genital double-somite about 1.8 times as long as wide (Fig. 4), anal somite with paired dorsal pore on posterior margin (Fig. 5). Caudal ramus about 3.5 times as long as wide (Fig. 5).

Among the oncaeid copepods, O. venusta was the most frequently found species in the surveyed area. It is an epipelagic form (Böttger-Schnack 2001) but it has been collected also from bathypelagic depths (Böttger- Schnack 1996, Nishibe et al. 2009), and our data indicate that they can dwell locally in shallow littoral conditions as well, probably as a result of passive transportation processes from adjacent shelf waters. The species is known for its high variability in total body length, ranging from 0.75 to 1.4 mm in the female and from 0.55 to 0.98 mm in the male (Böttger-Schnack and Huys 2004). Based on its size range the species has been categorized into 3 groups (Böttger-Schnack 2001, Böttger-Schnack and Huys 2004). Molecular studies using of 2 DNA markers (cyt b and ITS1) could differentiate 4 genetic clades where the small and large size groups were separated genetically and both could be deemed as distinct species (see Elvers et al. 2006, fig. 2, table 4). Therefore, some authors prefer to designate the group with the large size as O. venusta (960–1260 µm) and the smaller forms as O. venella (800–830 µm) (Wi et al. 2008); our specimens could be included in the first group.

The maximum size of our Colombian specimens (ca 0.96 mm) is not within the range of the typical form of the species, which is usually larger than 1 mm (see Böttger-Schnack and Huys 2004; table 1). In addition, these specimens possess a small dorsal swelling on the second pedigerous somite which is visible in lateral view (arrowed in Fig. 2) and indicates that the local population of O. venusta from Colombia belongs to the Atlantic form of the medium-sized group of the species (see Böttger- Schnack and Huys 2004; table 1).

Distribution. It is considered a cosmopolitan species (Razouls et al. 2005–2016) and has been recorded in the Indian, Atlantic, and Pacific Oceans at latitudes between 65° N and 45°S (Farran 1929, Malt 1983, Böttger- Schnack et al. 1989, Heron 2002, Böttger-Schnack and Huys 2004). In Colombia this species has been reported in the Pacific coast and in oceanic waters of the Colombian Caribbean: Magdalena, Guajira, and San Andres Island (Michel and Foyo 1976, Campos and Plata 1990, Bernal and Zea 2000, Martínez-Barragán et al. 2009, López and Mojica 2015). This is the first record from Rodadero Bay.

Oncaea scottodicarloi Heron & Bradford-Grieve, 1995 Figures 6–8