Pennaria disticha Goldfuss, 1820

Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, Journal of Natural History 56 (9 - 12), pp. 565-606 : 572-573

Pennaria disticha Goldfuss, 1820

( Figure 2a )

Pennaria disticha Goldfuss, 1820: 89 .

Type locality

Italy: Gulf of Naples (see Calder 2013, p. 7) .

Material examined

Chatham Bay, dock 004, 1 colony, 2.8 cm high, without gonophores, coll. G. Ashton, #266339.

Remarks

The hydroid of Pennaria disticha Goldfuss, 1820 has in the past been considered essentially cosmopolitan in tropical to temperate waters. While the species is known to be invasive, barcoding studies reveal the existence of cryptic species within the binomen ( Miglietta et al. 2015, 2019). In the analysis of Miglietta et al. (2019), specimens from the Pacific coast of Panama, in the Tropical Eastern Pacific, occurred in both a clade (1A) with other populations from Brazil, Florida, Hawaii, China Sea, and Mayotte in the Western Indian Ocean, and in another clade (2D) with specimens from North Carolina, the Caribbean, Atlantic Panama, Hawaii, Chuuk, Guam, American Samoa, and the Red Sea. Specimens from Italy (the type locality of the species) and elsewhere in the Mediterranean occurred in a separate clade (‘Clade 2C’), along with material from the Azores and the Gulf of Mexico. Taxonomic and nomenclatural issues arising from these results have yet to be resolved, however, and the name P. disticha has been retained for specimens examined here.

In the eastern Pacific, Pennaria disticha has been reported from San Francisco Bay, California, to Santa Elena Bay, Ecuador ( Fraser 1937, 1938a, 1938c, 1947, 1948, as Pennaria tiarella ). On the Pacific coast of Costa Rica, it has been reported from Port Culebra ( Fraser (1938a) and Bahía Huevos at 10.64444°N, 85.69167°W ( Kelmo and Vargas 2002). In the Galápagos Islands P. disticha is one of the most common and conspicuous species of hydroids on exposed coasts at depths ranging from the surface to 10 m, except on the westernmost Isla Fernandina (D. Calder, personal observations, 16–22 June 2001).

A species of many habitats, we regard P. disticha as cryptogenic in the Tropical Eastern Pacific (including in Cocos and the Galapagos Islands), pending further resolution of the taxonomy and geography of the multiple genetic clades detected to date.

Reported distribution

Cocos Island: first record.

Elsewhere: reported to be circumglobal in tropical and warm-temperate waters, although cryptic species appear to exist ( Calder 2010; Miglietta et al. 2015, 2019).

Figures

Figure 2. Anthoathecata: Pennariidae, Oceaniidae and Eudendriidae. (a) Pennaria disticha: hydranth, pedicel and part of hydrocaulus, #266339. (b) Corydendrium flabellatum: two hydranths and distal end of hydrocaulus, #266340. (c) Eudendrium cf. certicaule: hydranth and part of pedicel, #240637. (d) Eudendrium cf. certicaule: pedicel and hydranth with female gonophores, #240634. (e) Eudendrium cf. certicaule: pedicel and hydranth with male gonophores, #240636. (f) Eudendrium cf. certicaule: base of hydrocaulus with a branch, #240636. Scale bars: a, b, f = 0.2 mm; c–e = 0.1 mm.