Hippothoa divaricata Lamouroux, 1821

López-Gappa, Juan, Liuzzi, María G., Castro, Karen L., Bobinac, Magalí & Schwindt, Evangelina, 2022, Fouling bryozoans in Argentine harbours (Southwest Atlantic): new records and the description of a new species, Zootaxa 5205 (4), pp. 374-400 : 386

Hippothoa divaricata Lamouroux, 1821

( Figs 24–27 )

Hippothoa divaricata Lamouroux, 1821: 82 , pl. 80, figs 15, 16; Moyano, 1986: 101, pl. 1; Hayward & Ryland, 1999: 86, figs 16, 17A, B.

Material examined. MACN-In 43878, R / V Shinkai Maru, Campaign XI, Station 68, 48º27′ S, 65º27′ W, 103 m, March 5, 1979 . MACN-In 43888, Storni pier, Puerto Madryn, October 27, 2016, collected by Karen Castro.

Description. Colony encrusting, uniserial, branching, delicate. Each zooid usually gives rise to one distal and two disto-lateral zooids, the latter diverging from the parent zooid at oblique angles; sometimes there may also be two proximo-lateral branches. Zooids of three types: autozooids, female zooids and zooeciules. Autozooid length 522−765 µm, widest in the region of the disto-lateral buds, tapering distally and proximally, with a proximal slender cauda of variable length. Two distal septula give rise to the next autozooid in line. Three pairs of rounded pore chambers in the base of the lateral walls, two of them associated with buds. Autozooids and female zooids bearing a median longitudinal keel, which is the highest point of the frontal shield. Orifice longer than wide, placed beyond the highest point of the autozooid, slanted downwards towards the cauda of the next zooid; anter rounded, sinus Ushaped, condyles well-developed. Female zooids about the same size of autozooids, but with a shorter cauda; ovicell globular, bimucronate, with a pair of pseudopores in non-eroded specimens. Zooeciules small, narrow, elongated, arising from the usual budding sites of autozooids or female zooids; orifice ovate, distal.Ancestrula schizoporelloid, with smooth frontal shield, budding one distal, symmetric zooid.

Remarks. The delicate colonies of H. divaricata were growing on the shells of the ribbed mussel, Aulacomya atra . The species was previously unknown in fouling assemblages ( Ryland 1965; Gordon & Mawatari 1992; Harmelin 2014) and has not been found in Brazilian harbours and marinas ( Miranda et al. 2018; Xavier et al. 2021).

H. divaricata was recorded by Waters (1904) for Navarino Island in the Cape Horn region of southern Chile, but the specimen figured by him was collected in an Antarctic station. His Chilean material could actually belong to Neothoa patagonica ( Busk, 1852a) or N. chiloensis ( Moyano, 1982) , two common uniserial Magellanic hippothoids.

The material from Pernambuco, Brazil, identified as H. divaricata by Marcus (1939), was later regarded by Morris (1980) as belonging to a different species, H. brasiliensis , which lacks zooeciules and keeled autozooids.

Despite extensive sampling in the Magellan region, Moyano (1986) only found H. divaricata in northern Chile. López Gappa (1985) also did not find this species in his study of the Hippothoidae from Ría Deseado, Santa Cruz Province. Our material seems identical to Moyano’s Chilean specimens, both having a schizoporelloid ancestrula which buds only one mid-distal autozooid. We agree with Moyano’s (1986) view in that Viviani (1977) may have dealt with more than one species in his records of H. divaricata for the whole Chilean coast.

The New Zealand subspecies H. divaricata pacifica Gordon, 1984 , was recently raised to full species rank by Gordon (2020). It is characterized by a kenozooidal ancestrula, which gives rise to one distal ecaudate and two proximo-lateral long-caudate autozooids.

The presence of H. divaricata in a sample collected on the Patagonian shelf off Santa Cruz Province, at a depth of 103 m, suggests that this is a native species in Argentina. The morphology of the Southwest Atlantic material closely agrees with European descriptions of the species (e.g., Ryland & Gordon 1977; Hayward & Ryland 1999). However, its identification as H. divaricata is still not completely certain, as the ancestrula of the European material is unknown.

Distribution. Chubut and Santa Cruz provinces, Patagonia (this study). Widely distributed in the North Atlantic and the Mediterranean ( Hayward & Ryland 1999). Records beyond this region are doubtful due to taxonomic uncertainties.

Figures

FIGURES 24–27. FIGURES 24–27. Hippothoa divaricata; 24, zooeciule (arrowhead) (MACN-In 43873). 25, autozooid (MACN-In 43878); 26, ovicelled zooid (MACN-In 43878); 27, ancestrula and first zooid (MACN-In 43873). FIGURE 28. Fenestrulina delicia, ancestrula and early astogeny (MACN-In 43879). FIGURE 29. Cryptosula pallasiana, general aspect (MACN-In 43880). Scale bars. 24–27: 100 µm; 28: 200 µm; 29: 400 µm.