Cribrilina (Juxtacribrilina) flavomaris Yang, Seo, Min, Grischenko & Gordon, 2018

Yang, Ho Jin, Seo, Ji Eun, Min, Bum Sik, Grischenko, Andrei V. & Gordon, Dennis P., 2018, Cribrilinidae (Bryozoa: Cheilostomata) of Korea, Zootaxa 4377 (2), pp. 216-234 : 217-219

Cribrilina (Juxtacribrilina) n. subgen.

Type species. Cribrilina (Juxtacribrilina) flavomaris Yang, Seo, Min, Grischenko & Gordon n. sp.

Etymology. Latin juxta, near, close, next to, related, plus Cribrilina ; gender feminine.

Diagnosis. Colony encrusting, multiserial. Zooids with variably extensive frontal shield of pinnate costal spines, these with rows of intercostal lacunae, and at least one pseudopore, usually at tip; suboral costae stoutest, typically with frontally elevated tips. Articulated oral spines present. No avicularia. Ovicellate zooids in quincunx with autozooids and/or adventitiously borne and small or dwarfed; ooecium tending to be reduced, often small to vestigial, costa-like or flap-like, typically kenozooidal from maternal zooid, less commonly produced from distal autozooid, intimately associated with pair of transversely orientated proximofrontal costal spines, each typically with one or more pseudopores. Interzooidal communications via basal pore-chambers. Ancestrula costate like autozooids.

Remarks. Bishop (1994) remarked in his study of Cribrilina Gray, 1848 that it seemed unlikely that all species referred to this genus by previous authors are really (or strictly) congeneric. We agree. Inter alia, he highlighted the apparent concurrence of characters in two species that appeared related, Cribrilina annulata ( Fabricius, 1780) and Cribrilina spitsbergensis Norman, 1903 , namely the lack of avicularia, close application of two modified spines in ovicellate zooids that form a transverse ridge or crest on the ooecium, and possession of a cribrimorph ancestrula. Further, recent studies by Dick et al. (2005) and Grischenko et al. (2007) of putative C. annulata from the North Pacific, supplemented by our own observations, show that the composite structure of the ooecium and associated proximolateral costal spines is not precisely as in Cribrilina sensu stricto, though it may be homologous. In Cribrilina punctata (Hassall, 1841) , the type species of the genus, the ooecium is relatively large, has numerous pseudopores, and the distolateral pair of oral spines (non-articulated, and proximolateral with respect to the ooecium) are relatively short and project frontally or obliquely so, not meeting across the front of the ooecium. The equivalent spines in C. annulata arch across the front of the ooecium and fuse in the midline.

Additional to the differences between Cribrilina punctata and C. annulata , there is the huge amount of variability within the latter species. As Dick et al. (2005) noted, the numerous morphological differences across the attributed range of this species suggest several biological species. Our Korean material supports this suggestion, being different again from that reported by Dick et al. (2005) from Alaska and by Grischenko et al. (2007) from Hokkaido.

Ostrovsky (1998) made an excellent, detailed study of ovicellogenesis in C. annulata from the White Sea and our conclusions below have benefited from discussion with him. Further, thanks to the courtesy of Mary Spencer Jones (NHMUK), we have been able to examine SEM micrographs of C. annulata from the Norwegian type locality and several other localities (Shetland Is.; Nantucket, Massachusetts; Friday Harbor, Washington) as well as C. spitsbergensis . These confirm our interpretation of C. annulata as comprising more than one species. Our interim conclusion is that C. annulata from Norway, Shetland, the White Sea and Nantucket are conspecific, and that from Friday Harbor (see also Powell 1967) is a separate species allied to that described from Alaska by Dick et al. (2005). Two other species are also recognizable from the North Pacific, i.e. that from Hokkaido, and our material from the Yellow Sea (see below). Our comparison of the ooecia in all these forms, plus Ostrovsky’s (1998) studies, show them to be structurally related.

Bishop (1994) tabulated the main morphological characters of living and fossil Cribrilina . In comparing these characters with those in the range of forms that we now recognize in C. annulata sensu lato, we recognize what appear to be two main species clusters represented by Cribrilina sensu lato. The key characters comprise:

A ‘normal-sized’ (i.e. non-reduced) ooecium with numerous pseudopores; short latero-oral costae that do not cross the front of the ooecium to fuse in the midline; no adventitious dwarf zooids; avicularia; tatiform or cribrimorph ancestrula; i.e. Cribrilina (Cribrilina) . Included species: Cribrilina (C.) punctata (Hassall, 1841) (type), C. (C.) cryptooecium Norman, 1903 , C. (C.) watersi Andersson, 1902 , C. (C.) puncturata ( Wood, 1844) , C. (C.) mucronata Canu & Lecointre, 1927 , C. (C.) marylandica ( Ulrich & Bassler, 1904) , inter alia.

A reduced, often vestigial, ooecium, comprising a broad to narrow medial element with several or only 1–2 pseudopores; a pair of proportionately long protective latero-oral costae that cross the front of the medial element and fuse in the midline; adventitious dwarf zooids often present; no avicularia; cribrimorph ancestrula; i.e. Cribrilina (Juxtacribrilina n. subgen.). Included described species: Cribrilina (Juxtacribrilina) flavomaris Yang, Seo, Min, Grischenko & Gordon n. sp., C. (Juxtacribrilina) annulata ( Fabricius, 1780) n. comb., C. (Juxtacribrilina) corbicula O’Donoghue & O’Donoghue, 1923 , n. comb., Cribrilina (Juxtacribrilina) mutabilis Ito, Onishi & Dick, 2015 n . comb.

The distinctive transverse ridge on the front of the ooecium in C. (C.) cryptooecium was described by Bishop (1994) as having a “median lumen pore, which may remain widely open as lacuna for some time”; examination of his SEM images show that the pore/lacuna opens into the ooecial coelom, hence the transverse ridge does not represent fused latero-oral costal spines.

Note that the ooecium in both Cribrilina s.s. and Juxtacribrilina n. subgen. may be produced by the distal autozooid and/or kenozooidally from the maternal zooid. Bishop (1994) illustrated both kinds of originations in Cribrilina species, and Ito et al. (2015) showed that, in C. (J.) mutabilis , the medial element (‘ooecium proper’) of what they described as a ‘tripartite ooecium’ actually buds from the distal autozooid, which is not the case in adventitiously budded female zooids.

In C. (J.) flavomaris n. sp. we initially interpreted the ooecium as ‘tripartite’, comprising three costal elements. In fact, while the paired transverse elements do constitute costal spines, the median element, by homology with C. (J.) annulata s.s., does not; it represents a greatly reduced ooecial fold. In C. (J.) annulata s.s. the ooecial fold is much larger, but still smaller than in Cribrilina punctata . Hence, starting with C. punctata or a morphologically similar taxon, one can envisage the standard-sized ooecium as the starting point of a trend towards increasing reduction in ooecium size. A similar type of reduction has apparently taken place in the calloporid genus Cauloramphus Norman, 1903 (e.g. Dick et al. 2011), although none of its species has a ‘normal-sized’ ooecium. However, insofar as there is a distinctive cluster of morphologically similar species, some of them undescribed and masquerading under the name Cribrilina annulata , the question arises concerning the status of this cluster. Here we introduce for it Juxtacribrilina n. subgen. as an intrageneric clade name, i.e. a subgenus. Gene sequencing will clarify its status further; it is possible that it could be separated at full genus level, as the adelphotaxon to Cribrilina , or, less likely, as unrelated to Cribrilina s.s.

Our examination of SEM micrographs (NHMUK 1911.10.1.673, 674, respectively from Spitzbergen and Greenland) of what Bishop (1994) redescribed as Cribrilina spitsbergensis has revealed that this species belongs to Reginella , as Osburn (1950) perceived. Puzzlingly, Bishop did not mention Osburn’s publication or his new combination. Reginella spitsbergensis lacks articulated oral spines, having instead flattened, non-articulated laterooral processes. Additionally, its multiporous ooecium has a median suture.