Epibiotic association of encrusting cheilostome bryozoans on shells of an invasive mussel from rocky shores of South Africa, with the description of a new aviculiferous species of Chaperia Author Boonzaaier-Davids, Melissa K. Research and Exhibitions Department, Iziko Museums of South Africa, Cape Town, 8000, South Africa. Author Ma, Kevin C. K. Department of Zoology and Entomology, Rhodes University, Grahamstown, 6139, South Africa. & Department of Ocean Sciences, Memorial University of Newfoundland, St. John’s, A 1 C 5 S 7, Canada. Author Mcquaid, Christopher D. Department of Zoology and Entomology, Rhodes University, Grahamstown, 6139, South Africa. text Zootaxa 2023 2023-03-28 5258 2 197 210 http://dx.doi.org/10.11646/zootaxa.5258.2.2 journal article 10.11646/zootaxa.5258.2.2 1175-5326 7777040 250824EC-2DCE-4166-93C5-034D3D7399FD Chaperia atypica n. sp. ( Fig. 2A–F , Table 3 ) http://zoobank.org/ urn:lsid:zoobank.org:act: 1D5772C8-99E4-40B7-ADA6-DF404C2F1D0D Material examined. Holotype : SAMC-A094514 (dry), Seagulls ( 32°38′31.0″S , 28°25′41.5″E ), 8 March 2020 . Paratype : SAMC-A 094513, same details as the holotype . Other non-type specimens : SAMC-A 094511, Tenza Beach ( 32°22′37.8″S , 28°45′06.2″E ), 29 January 2020 . SAMC-A 094508 (on the same substratum as C. hyalina ), SAMC- A094509 (on the same substratum as C. hyalina ), SAMC-A 094512, Kei Mouth ( 32°41′03.4″S , 28°22′59.3″E ), 30 January 2020 . SAMC-A 094515-18, Kidds Beach ( 33°08′57.3″S 27°42′09.2″E ), 7 March 2020 . SAMC-A 094520-25, Schoenmakerskop ( 34°02′27.4″S , 25°31′59.5″E ), 5 August 2020 . SAMC-A 094528, St. Francis Bay ( 34°10′15.7″S , 24°50′06.2″E ), 4 August 2020 . SAMC-A 094630-34, Jeffreys Bay ( 34°01′35.5″S , 24°55′52.2″E ), 3 August 2020 . All material was collected by K.C.K. Ma and is kept dry. Additional comparative material examined: Chaperia capensis (Busk, 1884) , SAMC-A026485 , station SM 179 ( 33°30.3′S , 27°22.1′E ), off Great Fish River Mouth , Southeast Coast , South Africa , dredged, depth 80 m , 29 May 1978 . Chaperia septispina Florence, Hayward & Gibbons, 2007 , SAMC-A028571 , Homestead Plateau , Oudekraal (33°58′90″S, 17°15′00″E), depth 12 m , collected by W. Florence , 30 April 1999 . Etymology. From the Latin a- plus typica , meaning atypical, not usual, and referring to the atypical diagnostic features noted in this new Chaperia compared to other species of the genus. Diagnosis. Colony encrusting. Cryptocyst typically granular, extensive; gymnocyst reduced or absent. Suborificial occlusor laminae well-developed. Spines on distal rim. Interzooidal avicularia and vestigial ooecia present. Pore chamber windows present. Description. Colony encrusting, unilaminar, multiserial, usually forming small patches, some colonies up to 30 mm in diameter (see Table 2 ). Dried (unbleached) material light brown to creamy white. Autozooids arranged quincuncially ( Fig. 2A ), rounded distally, widest at one third to half zooidal length, with a pair of distal and one lateral pore chamber windows, approximately at autozooid mid-length ( Fig. 2B ). Cryptocyst well-developed, occupying nearly the total length of autozooid, a raised rim outlining the autozooids, sometimes with the distal part of the opesia raised; frontal surface granular, grain size 4–12 μm in diameter (N T = 60). Reduced or negligible gymnocyst. Opesia eye-shaped with a pair of well-developed occlusor laminae ( Fig. 2C ); 6–8 oral spines, more commonly seven (N T = 20; length range = 0.17–0.35 mm ; 12–28 μm in diameter) distributed evenly around the distal part of the opesia in a shallow arc ( Fig. 2E ), ending more or less at level with the proximal border of the opesia. Interzooidal avicularia present, twinned or single, each situated disto-medially, projecting into the next distal zooid, distally directed, oval-shaped, the rostrum rounded, with condyles as mandibular pivots ( Fig. 2D ), more or less situated mid-length of the avicularium. Intramural budding observed ( Fig. 2D ). Ooecia as a transversely narrow rim on the distal border of opesia with ooecial pore located medio-distally ( Fig. 2E, F ). Ancestrula not seen. Remarks. This species is confidently placed in the genus Chaperia due to the presence of the eye-shaped opesia not exceeding 50% of the zooidal length, extensive cryptocyst, stout spines around the distal oral border and well-developed occlusor laminae as described in Gordon (1982) . Avicularia and ovicells were not reported in the original genus description by Jullien (1881) and subsequent observations made by Gordon (1982) . However, interzooidal avicularia and vestigial ooecia were recently observed in some Chaperia species from New Zealand (D.P. Gordon, personal communication, 27 July 2022 ). These features differ from those of Chaperiopsis species that have an oval opesia generally occupying 75% or more of the zooidal length, narrow cryptocyst, negligible occlusor laminae and the presence of frequent small avicularia and prominent hyperstomial ovicells ( Gordon 1982 ). Chaperia acanthina Lamouroux, 1824 ( C. australis Jullien, 1881 by original designation, p. 62), originally described from Falkland Islands in the South Atlantic, was also reported from South Africa ( O’Donoghue & de Watteville 1937 ; O’Donoghue 1957 ; Hayward 1980 ). Chaperia atypica n. sp. differs from this species in the shape of the opesia, in the position and number of spines, and in having a reduced gymnocyst. However, records of C. acanthina in South Africa are in need of revision (D.P. Gordon, personal communication, 13 September 2022 ) and also discussed in Hayward & Cook (1983 , p. 19). Two species of Chaperia are known from South Africa , namely C. capensis and C. septispina . An additional species, C. polygonia Kluge, 1914 is known from Antarctica in the Southern Ocean. Chaperia atypica n. sp. has 6–8 distolateral spines, while C. acanthina has 4–5 distal spines, C. polygonia 5–6, C. septispina 5–7 and C. capensis only two. This new species is the first Chaperia with avicularia and the first South African species with ooecia. Four out of nine C. atypica n. sp. colonies examined using SEM (SAMC-A094513, SAMC-A094516, SAMC-A094524 and SAMC-A094525), indicated the presence of avicularia, usually one or two interzooidal avicularia scattered sporadically in a colony of at least 20 autozooids. One colony (SAMC-A094513), with at least 40 autozooids, had four autozooids associated with a single interzooidal avicularium, and one associated with twinned avicularia (see Fig. 2D ). These avicularia differ in shape and frequency from those in Chaperiopsis : they are rare and with rounded rostra ( Fig. 2D ), as opposed to the frequent avicularia with triangular rostra and pedunculate avicularia usually present for example in Chaperiopsis multifida (Busk, 1884) , a species reported from South Africa (e.g. Marcus 1922; O’Donoghue & de Watteville 1935; Hayward & Cook 1983 ; Florence et al. 2007 ) and also New Zealand ( Gordon 1984 ). Vestigial ooecia (as seen in Fig. 2E, F ) have also been reported from an Australian Chaperia sp. (see Cook et al. 2018 , p. 107, fig. 3.44A) and are likely to be typical of the genus but previously overlooked. To date, this species has only been observed forming encrusting patches on the invasive mussel M. galloprovincialis , distributed on rocky shores from Tenza Beach to St. Francis Bay on the southeast coast of South Africa .