Stephanollona boreopacifica Yang, Seo & Gordon, 2018

(Figs 33–36)

Stephanollona boreopacifica Yang et al. 2018: 510, figs 32–34.

Material examined. MACN-In 43884, San Antonio Este harbour, November 29, 2018, collected by Evangelina Schwindt.

Description. Colony encrusting, multiserial, mostly unilaminar, but frontal budding may occur in central areas of large colonies.Autozooids with clear boundaries and regularly oriented only near the growing edge; with indistinct limits and unordered in central areas of mature colonies. Frontal shield nodular, surrounded by 7–14 marginal areolar pores. Orifice cleithridiate; distal and lateral rims of anter beaded; sinus broadly U-shaped; condyles on sloping proximolateral shoulders of anter. Oral spines 5–6, long, cylindrical, only their basis remaining in ovicellate zooids. Avicularia adventitious, dimorphic, 1–2 per zooid, absent near the growing edge; avicularian cystid swollen, protruding. Smaller avicularia oval, obliquely orientated, with serrated rostral rim, thin crossbar, and ligula on rostral side of crossbar. Larger avicularia directed disto-laterally, rostrum elongate-triangular with rounded tip and extensive palatal shelf; opesial foramen semicircular; rostral foramen triangular, bordered by smooth cryptocyst, with a relatively long ligula projecting from the crossbar. Ooecium initially recumbent on distal zooid, its shape later obscured by secondary calcification, with rounded triangular frontal tabula and very short labellum; associated avicularia may occur on the ooecium in central parts of mature colonies. Ancestrula not seen.

Remarks. Stephanollona boreopacifica was previously known only from its original description. The disjunct geographic distribution and the appearance in a fouling assemblage of a Patagonian harbour suggests that this species should be regarded as a NIS that probably arrived in Argentina by maritime traffic.

Distribution. South Korea (Yang et al. 2018), Río Negro Province, Argentina (this study). This is the first record of the species for the Southern Hemisphere and the Atlantic Ocean.