Beroe gracilis Künne, 1939

Oliveira, Otto M. P., Feliú, Guillermo & Palma, Sergio, 2014, Beroe gracilis (Ctenophora) from the Humboldt Current System: first occurrence of this species in the southern hemisphere, Zootaxa 3827 (3), pp. 397-400 : 398-399

Beroe gracilis Künne, 1939

( Fig. 1 , Table 1)

Beroe gracilis Künne, 1939 — Greve 1975 1981; Greve & Reiners 1988; Greve et al. 2004; Tamm & Tamm 1993; Wrobel & Mills 2003; Mills & Haddock 2007; Hosia et al. 2011.

Beroe sp.— Palma 1994; Palma & Rosales 1995.

Material examined. September 1989: Off Central Chile. 32°–33° S, few specimens, reported in Palma (1994) as Beroe sp. (as B. gracilis in figure 9). October–November 1990: Valparaíso Bay, Chile, 17 specimens, reported in Palma & Rosales (1995) as Beroe sp. 11 November 2013: Off Dichato, Tomé, Chile, 36°30’ S, 73°05’ W, R. Riquelme collector, 11 specimens, Fig. 1 , fixed in 4% formalin (Ctenophora collection of ZooTaxa Millennium Institute of Oceanography, access number ZOOTIMO201401). 14 November 2013: Off Dichato, Tomé, Chile, 36°30’° S, 73°05’ W, R. Riquelme collector, three specimens observed and photographed alive.

Total length of body 11.0 mm

Maximum width of body 5.2 mm

Length of subtentacular ctene rows 3.6–4.8 mm Length of substomodeal ctene rows 4.1–5.0 mm Width of mouth 4.6 mm

Number of ctene plates in subtentacular ctene rows 29–32

Number of ctene plates in substomodeal ctene rows 36–41

Length of polar field 1,080 Μm Number of papillae 8

Length of papillae up to 160 Μm Diameter of meridional canals up to 490 Μm Diameter of paragastric canals up to 165 Μm Diameter of circular canal up to 98 Μm Width of ctene plates 115–510 Μm Length of ctene plates up to 552 Μm Distance between ctene plates 112–131 Μm Diameter of statocyst dome 233 Μm Description of Dichato specimens. Sac-shaped body, elongated in the oral-aboral axis, rounded both at oral and aboral ends. Body compressed in the tentacular plane. Eight meridional canals extending from the aboral region towards the mouth, directly connected with a circular canal around the mouth. No lateral diverticula observed along the meridional canals. Ctene rows located above the meridional canals, arising at the aboral region. Substomodeal and subtentacular ctene rows of almost equal length, extending for about 1/3 to half the length of the meridional canals to the oral region. Mouth wide, semicircular, extending the whole oral region, opening into a large pharynx that occupies most of the central inner part of the animal. Two opposite paragastric canals, extending from the aboral pole of the pharynx to the circular canal around the mouth at the tentacular plane. Apical organ composed of a statolith at the center of the polar fields, with unbranched aboral papillae, not longer than the statolith dome. Male gonads formed at the lateral walls of the meridional canals. No female gonads present in the specimens observed. Macrocilia arranged in a broad band along the oral portion of the pharynx.

Biological notes. The specimens observed alive were fast swimmers, apparently always searching for potential prey. In the same plankton sample, many Pleurobrachia bachei specimens were observed, some of them damaged, possibly by the predatory action of B. gracilis .

Remarks. The Chilean specimens of B. gracilis are not as slender as those described from other areas. The descriptions provided by Künne (1939), Greve (1975), Wrobel & Mills (2003) and Mills & Haddock (2007) show specimens three times longer than their maximum width. The specimens observed in this study are no longer than two and a half times their maximum width. However, other characteristics like the absence of diverticula and the shape of the oral and aboral ends match the descriptions of Künne (1939), Wrobel & Mills (2003) and Mills & Haddock (2007). The specimens observed in this study also present a broad band of macrocilia inside the lips, just as described by Tamm & Tamm (1993, p. 80) for B. gracilis but different from the patterns expected for the juveniles of other sympatric species, like B. cucumis and B. forskalii (cf. Tamm & Tamm 1993; Oliveira & Migotto 2014).

We found this species in plankton samples collected in 1989 and 1990 and collected it again in 2013. We believe that this species is an only-recently-recognized normal member of the superficial zooplankton off Chile, and should not be construed as an alien, introduced species. The absence of other records of B. gracilis for the Pacific coast of South America in the exhaustive revision of Oliveira et al. (in press) can possibly be attributed to the absence of ctenophore taxonomists in the area.

Distribution. This species was originally described from the North Sea ( Künne 1939) and is also found in the northern Atlantic ( Greve 1975; Greve et al. 2004) and Pacific oceans ( Wrobel & Mills 2003; Mills & Haddock 2007). Although Wrobel & Mills (2003) recorded the species as “probably worldwide in cold water”, this is the first official record for the southern hemisphere.

Figures

FIGURE 1. Beroe gracilis Künne, 1939: preserved specimen from Dichato, Chile (ZooTaxa Millennium Institute of Oceanography collection, ZOOTIMO 201401). View of whole specimen in stomodeal plane. Legend: cc, circular canal; mo, mouth; pc, paragastric canal; sscr, substomodeal ctene row; stcr, subtentacular ctene row; stmc, subtentacular meridional canal.