Arbocuspis bellula was described from 'Australia', and has been recorded from warm waters from the Gulf of Mexico and Caribbean to China. It is likely that this is a multi-species complex.
Image below of algal epiphyte from Saint Francis Is., South Australia. This material is closest to Hincks' variety "multicornis", although there are only two branched spines, and the other spines appear different from Hincks' drawings. Thanks to Jan Watson for collection.
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SEM image of algal epiphyte from Saint Francis Is., South Australia. This material is closest to Hincks' variety "multicornis", although there are only two branched spines, and the other spines appear different from Hincks' drawings. Thanks to Jan Watson for collection. |
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SEM image of material from Florida. Thanks for the image to Judith Winston, Virgina Museum of Natural History, and Eliza C. Winston |
Reference: Hincks, T.H., 1881. Contributions towards a general history of the marine Polyzoa. IV. Foreign Membraniporina (second series). Ann. mag. nat. hist. (5) 7: 147-161.
Membranipora bellula n. sp.
Hincks, 1881 (Pl. VIII. figs. 4, 4a, 4b.
"Zooecia pyriform, rounded and expanded above, and narrowing of to the base; area occupying about half the length of the cell wholly filled in with membrane, subelliptical, broad below and narrowing very slightly upwards to the top, where the semicircular orifice is placed, flanked on each side by two tall erect spines; on the lower margin a single, much-branched spine, which spreads over the aperture, forming an antler-like operculum; sometimes a very long corneous spine, springing from a raised socket, a little below the inferior margin; a portion of the cell below the area, which is sometimes a good deal elongated, smooth and shining, and covered with numerous delicate spinules. Ooecia none."
"Var. α (bicornis) (Now Arbocuspis bicornis). With two opercular spines on the lower margin, of small size and slightly branched, placed one on each side of a short, sharply pointed central mucro rising from a prominent boss; a single spine only on each side of the orifice; no spinules or horny appendages; surface smooth, white, and very polished."
"Var. β (multicornis) (Now Arbocuspis multicornis). Opercular spines 3-5, placed closely together, their numerous dichotomous branchlets combining to form a beautiful protective shield, which extends to the base of the oral valve."
"Loc. Australia, normal and var. multicornis; Ceylon, var. bicornis; Madagascar (Miss Jelly); St. Vincent, Cape-Verd Islands (Miss Gatty). M. bellula always occurs creeping over weed, and frequently runs out into narrow strap-like segments."
"This is an exquisite species, which seems to be far from uncommon in various parts of the world; and it is difficult to understand how it is that it has remained so long undescribed. I cannot recollect, however, to have met with any published account of it, although it has been known to collectors under a manuscript name. It is a species which varies much in appearance, the changes being chiefly due to the presence or absence of the spinous appendages; and especially to the modification of the opercular spine. The principal varieties have already been noticed. In some cases the tall corneous spine rising from a distinct socket, which is so characteristic of M. pilosa (from which the present form is probably derived), makes its appearance; in others the zoarium bristles with immense numbers of slender spinules; in others, again it has neither seta nor spinule. In a curious form from Madagascar the edges of the narrow segments into which the zoarium divides are fringed by very tall and slender setae frequently placed in pairs, whilst there is also a profusion of the suboral appendages. This form presents a very marked contrast to the extremely simple and elegant variety (bicornis) from Ceylon. The same variability in the spinous armature is characteristic of M. pilosa."
Description from Hayward & Ryland, 1995.
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