Obelia dichotoma
Creators: name: Galea, Horia R.
Publisher: name: Zenodo
Year: 2007
Subjects: Biodiversity
Taxonomy
Animalia
Cnidaria
Hydrozoa
Leptothecata
Campanulariidae
Obelia
Obelia dichotoma

description: Obelia dichotoma (Linnaeus, 1758)   
(fig. 21H–J, table 39)  
 Sertularia dichotoma Linnaeus, 1758: 812.   
 Obelia dichotoma: Hincks, 1868: 156, pl. 28 fig. 1; Fraser, 1912: 362, fig. 22; Nutting, 1915: 80, pl. 20 fig. 7; Stechow, 1919: 49; 1923: 117; Fraser, 1944: 28, fig. 127; Picard, 1951: 347; Rees & Rowe, 1969: 17; Calder, 1971: 55, pl. 4B; Leloup, 1974: 18; Calder, 1975: 303, fig. 4D; Cornelius, 1975: 265, figs 3–4; Millard, 1975: 227, fig. 75F–J; Morri, 1981: 66, fig. 21; Cornelius, 1982: 117; Hirohito, 1983: 16; Gili et al., 1989: 107, fig. 32A–B; Calder, 1991: 72, fig. 38; El Beshbeeshy, 1991: 111, fig. 25B; Ramil & Vervoort, 1992: 243, fig. 68C; Cornelius, 1995b: 296, fig. 69; Hirohito, 1995 (English text): 74, fig. 21D–K; Migotto, 1996: 88, fig. 16D; Ramil et al., 1998a: 200; Medel & Vervoort 2000: 49, fig. 10C–D; Schuchert, 2000: 413; 2001a: 155; Peña Cantero & García Carrascosa, 2002: 161, fig. 31B–C; Calder et al., 2003: 1202; Kelmo & Attrill, 2003: 138, fig. 6G–I; Vervoort & Watson, 2003: 425, fig. 104A– E; Bouillon et al., 2004: 200, fig. 114C–G; Calder & Kirkendale, 2005: 487; Vervoort, 2006: 273.   
 Obelia australis Hartlaub, 1901: 367; Ralph 1957: 830, fig. 4A–H.   
 Obelia nodosa Bale 1924: 230, fig. 1; Ralph 1957: 832, fig. 5I–K; 1961: 109.   
 Laomedea dichotoma: Vervoort, 1959: 315.   
 Campanularia obtusidens Jäderholm, 1904a: 2, pl. 1 fig. 1.   
 Material examined. Stn. CHL 02 —04.iii.2005, 13– 20 m, S80: small, fertile colonies, epizoic on Symplectoscyphus filiformis. Stn. COM 01 —27.i.2006, 17– 23 m, S97: several fertile colonies, up to 4.5 cm high, on unidentified substrate; 28.i.2006, 0–6 m, S92: a small, sterile colony, about 0.5 cm high, on mollusc shell. Stn. COM 02 —22.i.2006, 20– 25 m, S98: basal parts of several main stems, without side branches, on polychaete tube. Stn. COM 06 —26.i.2006, 20– 23 m, S95: several small, sterile colonies, less than 1.5 cm high, on wood or epizoic on Sertularella polyzonias. Stn. COM 07 —09.iii.2005, 10– 25 m, S56: several colonies, up to 11 cm high, with only the perisarc left. Stn. COM 08 —18.i.2006, 18– 22 m, S160: several sterile stems, up to 0.8 cm high, epizoic on Bougainvillia pyramidata; S164: several sterile colonies up to 8 cm high. Stn. COM 09 — 04.v.2005, S49 (12 m): several sterile stems about 4 cm high, on wood, 2 slides (MHNG INVE 53221); S11 (14 m): several sterile stems, up to 5.5 cm high, on wood (MHNG INVE 53164); S6 (14 m): several fertile stems, up to 5 cm high, on wood (MHNG INVE 53159). Stn. COM 11 —11.ix. 2004, 24 m, S17: several sterile colonies, 3–8 cm high, on rock (MHNG INVE 53170). Stn. COM 12 —09.x.2004, S36 (13 m): several sterile stems up to 6.5 cm high, on wood (MHNG INVE 53200); S16 (13 m): one sterile colony 6.5 cm high, on dead gorgonian (MHNG INVE 53169); S13 (20 m): numerous fertile stems, up to 10 cm high (MHNG INVE 53165). Stn. COM 14 —26.ii.2005, 10– 15 m, S61: four sterile fragments, 2–5 cm high. Stn. MEL02, 06.iii. 2005, 15 m, S81: small, fertile colonies, up to 1 cm high, epizoic on Symplectoscyphus filiformis; S43: several sterile colonies about 6 cm high (MHNG INVE 53209); S78: small, sterile colony, less than 1 cm high, epizoic on Symplectoscyphus subdichotomus. Stn. MEL 03 —08.iii.2005, 20– 30 m, S82: several fertile colonies, 1–2 cm high; S51: one fertile colony, ca 5.5 cm high, polysiphonic basally (MHNG INVE 53225); S90: several fertile colonies, less than 1 cm high, epizoic on Symplectoscyphus filiformis. Stn. IVM — 28.iii.2005, S46 (8 m): several fertile colonies, up to 1.5 cm high, epizoic on Bougainvillia pyramidata; S35 (8 m): several fertile colonies, up to 8 cm high, epizoic on Bougainvillia pyramidata (MHNG INVE 53198); S26 (20 m): one fertile colony, 2.5 cm high, epizoic on Bougainvillia pyramidata (MHNG INVE 53182); S32 (25 m): several fertile colonies about 3 cm high, epizoic on Bougainvillia pyramidata (MHNG INVE 53190). Stn. CME — 28.iii. 2005, 12 m, S62: one sterile colony, about 3.5 cm high, on gorgonian; S50: several sterile colonies, 2.5–6.5 cm high, on dead gorgonian (MHNG INVE 53223). Stn. CFQ — 29.iii. 2005, 32 m, S73: several fertile colonies, up to 2.3 cm high, on gorgonian; S45: one small, fertile colony, ca 1 cm high, on stems of unidentifiable tubulariid. Stn. T 16 —25.iii. 2005, 12 m, S42: several colonies with only the perisarc left. Stn. ANI — 01.iv. 2005, 2 m, S41: several sterile colonies, up to 15 cm high, 3 slides (MHNG INVE 53205). Stn. SWA 15.iii.2006, S134 (20 m): several fertile colonies and fragments, up to 3 cm high; S127 (24 m): several fertile colonies 4–5 cm high, epizoic on Hybocodon chilensis. Stn. CAD — 12.iii. 2006, 15 m, S113: several fertile colonies, up to 3.5 cm high. Stn. CCA — 12.iii. 2006, 28 m, S87: several sterile stems, on gorgonian. Stn. CFA — 14.iii.2006, S147 (10 m): several sterile stems 1–2 cm high, epizoic on Bougainvillia pyramidata; S125 (15 m): several small, sterile colonies, epizoic on Bougainvillia pyramidata; S88 (10–33 m): small, sterile colonies 1–2 cm high. Stn. ILA — 13.iii. 2006, 32 m, S130: one sterile colony about 5 cm high, on polychaete tube. Stn. ICA – 13.iii. 2006, 20 m, S139: several fertile colonies, up to 6 cm high. Stn. PAB — 10.iii. 2006, 20 m, S85: a few sterile stems, less than 1 cm high, epizoic on Symplectoscyphus subdichotomus. Stn. CCO — 09.iii. 2006, 18 m, S144: small, sterile colonies and fragments. Stn. CAR — 08.iii.2006, 15– 25 m, S152: small, sterile colonies up to 1.5 cm high, epizoic on Bougainvillia pyramidata. Stn. CPA — 09.iii. 2005, 15 m, S170: small, sterile colonies, less than 1 cm high, epizoic on Symplectoscyphus subdichotomus. Stn. CVI — 06.iii.2006, 15– 25 m, S142: several sterile colonies, up to 16 cm high.   
 Type locality. “In Oceano” (Linnaeus, 1758), specifically the southwest coast of England.   
 Remarks. Complete redescriptions of O. dichotoma and synonymy are provided by Calder (1991) and Cornelius (1982, 1995b). The present material has hydrothecae with shallow, rounded cusps, the diaphragm is transverse to oblique in lateral view, and the tentacle nematocysts are long and banana-shaped, which agrees well with the concept of species defined by Cornelius (1982, 1995b).   
 Hydroid epibionts. Bougainvillia pyramidata (Forbes & Goodsir, 1851); Calycella syringa (Linnaeus, 1767); Phialella cf. quadrata (Forbes, 1848); Modeeria rotunda (Quoy & Gaimard, 1827); Filellum serratum (Clarke, 1879); Clytia paulensis (Vanhöffen, 1910).   
 World distribution. This species has a cosmopolitan distribution (Vervoort 2006).   
 Records from Chile. Previous records are from the Guaitecas Islands, Melinka (Jäderholm 1904a), Tocopilla, Coquimbo Bay, San Vicente Bay, Seno Reloncavi, Golfo de Ancud (Leloup 1974). The present material was collected at nearly all the stations, roughly from 42° to 52° S.
description: Published as part of Galea, Horia R., 2007, Hydroids and hydromedusae (Cnidaria: Hydrozoa) from the fjords region of southern Chile, pp. 1-116 in Zootaxa 1597 (1) on pages 91-93, DOI: 10.11646/zootaxa.1650.1.4, http://zenodo.org/record/5097970