Hincksina Norman, 1903

Berning, Björn, Spencer Jones, Mary E. & Vieira, Leandro M., 2021, Revision of the European species of the genus Hincksina Norman, 1903 (Bryozoa, Cheilostomatida, Flustridae), Zootaxa 5081 (3), pp. 333-352 : 334-335

Genus Hincksina Norman, 1903

Hincksina Norman, 1903: 585 ; Osburn 1950: 41; Prenant & Bobin 1966: 200; Zabala & Maluquer 1988: 80; Hayward & Ryland 1998: 152.

Type species. Membranipora flustroides Hincks, 1877 by original designation.

Revised diagnosis. Colony encrusting, budding of zooidal type. Zooecia well calcified, communication via uniporous septula. Narrow gymnocyst present but variably developed, cryptocyst reduced to practically absent. Cylindrical or flattened oral as well as mural spines of variable shape encircling the opesia, spines in late astogenetic zooids may be branched and/or dimorphic to polymorphic in some species, spine bases jointed or fully calcified. Brooding in endozooidal ovicells positioned in the proximal part of a distal autozooid or an avicularium, not closed by the operculum but by an ooecial vesicle, ooecium a short hood formed by the proximal cystid of the distal zooid or avicularium, ectooecium and endooecium calcified. Avicularia interzooidal, occasionally vicarious; rostrum round or pointed, palatal opesia framed by an immersed calcified shelf, mandible hinged on a pair of lateral teeth. Kenozooids, which replace an autozooid or avicularium, may occasionally be present. Ancestrula tatiform.

Remarks. Most Hincksina species have avicularia with rounded rostra and mandibles, which was accounted for in the most recent generic diagnosis by Hayward & Ryland (1998, p. 152). The two species from the Azores revised here ( H. alice and H. neptuni ) and also several fossil species assigned to this genus [e.g. Hincksina acutirostris Canu & Lecointre, 1927 ; Hincksina loxopora ( Reuss, 1847) ], however, have avicularia with elongated, triangular rostra and pointed tips. As all other zooidal, avicularian and ovicell characters are identical, the generic diagnosis is here augmented to also include this avicularium morphotype, as avicularium shape does generally not justify a separation at genus level.

In the amended diagnosis, a distinction is also made between the vertically directed oral spines and the overarching mural spines. Variability in spine shape may be considerable and present at different levels. Within a zooid, shape and size usually differs between proximal and distolateral mural spines, and usually the pair of oral spines differs from the mural ones in morphology and/or orientation. In species in which the adult zooids have non-cylindrical or non-subclavate mural spines, there is a distinct astogenetic gradient from simple cylindrical spines in the firstgeneration zooids towards more complex spine morphologies in adult zooids. Intracolonial variability is therefore extensive in some species. But even between adult zooids within the same colony, spine shape and size may differ significantly, e.g. in zooids growing on the upper vs. the lower side of the same rock (see Souto et al. 2014, fig. 3E, F). This intraspecific variability is obviously being controlled by (micro)environmental factors such as the presence of predators, current speed, or abrasive bedload, as has previously been shown to be the case in anascans that need to protect the vulnerable frontal membrane from being damaged (e.g. Harvell 1991; Bayer et al. 1997). The pronounced ecophenotypic variability may thus render it difficult to precisely define morphospecies taxa in Hincksina . In order to delimit intra- from interspecific variability, future systematic research on this group will certainly have to involve genetic analyses, and to investigate numerous colonies from different (micro)environments.