Clytia gracilis

Clytia cf. gracilis (M. Sars, 1850)

Figs. 7 H–K

Laomedea gracilis M. Sars 1850: 138.

Clytia cylindrica L. Agassiz 1862: 306, figs. 41–44.— Fraser 1938a: 30; Fraser 1948: 206.

Campanularia attenuata Calkins 1899: 350, pl. 2, figs. 9, 9a, 9b, 9c, pl. 6, fig. 9d.

Gonothyraea gracilis.— Fraser 1938a: 35; Fraser 1938b: 109; Fraser 1938c: 132; Fraser 1948: 212.

Clytia attenuata.— Salcedo-Martínez et al. 1988: 13.

Clytia gracilis.— Bastida-Zavala et al. 2013: 344.— Humara-Gil & Cruz-Gómez 2018: 458, fig. 4.

Type locality. Norway: Lofoten (Calder 1991a; Schuchert 2001).

Material examined. Polyp—PB7_28, sampling site 1 (1), immature, 27°C, on algae and ascidian.

Description. Colonies stolonal. Polyps up to 2 mm high arising from creeping hydrorhiza at irregular intervals. Pedicels usually long (1082.1 μm), with 8–10 annulations at the base and 2–3 annulations below the hydrotheca, smooth in the middle. Hydrotheca cylindrical, 446.9 μm long, 232.3 μm wide at the margin, 98.4 μm wide at the diaphragm, with thin perisarc. Margin with 8–10 acute triangular cusps, slightly tilted. Hydrothecal diaphragm thin, transverse.

More detailed description in Calder (1991a), Cornelius (1995), and Schuchert (2001).

Taxonomic status. Accepted. AphiaID 117367.

Remarks. Clytia gracilis (M. Sars, 1850) has a complicated taxonomic history, resulting from the few morphological characters available for diagnosis, and wide intraspecific variation (Cornelius 1995; Cunha et al. 2020). The polyp of the species is traditionally distinguished by its hydrotheca with pointed cusps and smooth gonotheca, in contrast with the rounded cusps and spirally grooved gonotheca usually distinctive of C. hemisphaerica (Linnaeus 1767) (see Calder 1991a; Cornelius 1995). However, recent molecular and life cycle studies have shown that some of the characters attributed to C. gracilis may be distinctive of different lineages, contributing to the validation of former synonyms and the description of new species (Lindner et al. 2011; Zhou et al. 2013; He et al. 2015). Nonetheless, the traditional concept of C. gracilis is still known to comprise multiple cryptic lineages (Cunha et al. 2017), and the delimitation of the typical species is still unclear. As a result, this is a tentative identification, pending more detailed studies with molecular and life cycle data.

We followed Calder (1991a) and Schuchert (2019) and considered the records of C. cylindrica from Fraser (1938a, 1948) as C. gracilis (M. Sars, 1850). Our specimens are also very similar to specimens of C. cf. gracilis recently described by Humara-Gil & Cruz-Gómez (2018) from the coast of Oaxaca, especially regarding the size of the hydrotheca and morphology of the cusps. As noticed by Humara-Gil & Cruz-Gómez (2018), specimens of C. cf. gracilis from the Pacific coast of Mexico have smaller hydrotheca than specimens described by Calder (1991a) and Schuchert (2001, 2003). Similarly, the hydrothecal cusps of our specimens are not as tilted as the ones described by Cornelius (1995) and Schuchert (2001, 2003). Nevertheless, these characters usually present wide intraspecific variation and may not be informative for the delimitation of the different lineages of C. gracilis (see Cunha et al. 2020).

Distribution. In its traditional concept, C. gracilis is considered nearly cosmopolitan (Cornelius 1995; Schuchert 2001), but this assumption must be revisited considering that it is a species complex (see Cunha et al. 2017). In the Pacific coast of Mexico, it has been reported in Baja California (Isla Partida and Angel de la Guarda Islands) (Fraser 1948), Baja California Sur (Bahía Concepción, Dewey Channel, Natividad Island and San Marcos Island (Fraser 1938b; Fraser 1948), Sonora (Ensenada de San Francisco, Guaymas and Rocky Point) (Fraser 1948), Nayarit (Isabel Island) (Fraser 1938a), Jalisco (Navidad Head) (Fraser 1938a), Guerrero (Chololo, Godornia, Morro Tigre, White Friars) (Fraser 1938a; Salcedo-Martínez et al. 1988), and Oaxaca (Chacahua Bay and Tangola-Tangola Bay) (Fraser 1938a; Fraser 1938c; Humara-Gil & Cruz-Gómez 2018).