Cribrilina corbicula: O’Donoghue and O’Donoghue 1926 , p 51

Dick, Matthew H., Grischenko, Andrei V. & Mawatari, Shunsuke F., 2005, Intertidal Bryozoa (Cheilostomata) of Ketchikan, Alaska, Journal of Natural History 39 (43), pp. 3687-3784 : 3720-3721

Cribrilina corbicula: O’Donoghue and O’Donoghue 1926, p 51 ; Osburn 1950, p 178.

Description

We found one young colony at Ketchikan; description is based on that specimen and others from SERC settling plates from Sitka, Alaska.

Colony. Unilaminar, with scattered frontally budded dwarf zooids; flexible; golden brown in colour.

Zooids. Oval to spindle-shaped; 0.40–0.64 mm long (average 50.517 mm, n 520, 3) by 0.25–0.34 mm wide (average 50.298 mm, n 520, 3); loosely appressed, separated by a groove.

Frontal wall. Frontal shield highly convex, composed of 10–14 coarse, somewhat flattened costae that meet at an irregular suture in midline; between adjacent costae on each side are usually two large intercostal pores in addition to marginal pore, thus six pores in transverse series across widest part of zooid; pores variable in shape (irregular, circular, oval, or inverted heart-shaped), their maximum dimension often greater than width of intercostal struts between them. Non-ovicellate zooids have distalmost pair of costae less flattened than the rest, forming proximal margin of orifice, the somewhat acute tips often rising at the midline to form a suboral mucro. Ovicellate zooids in primary layer have suboral costae markedly thickened, their blunt tips either forming a bilobed suboral mucro ( Figure 7D ) or flattened in the transverse plane, rising as paddle-like projections meeting in the midline ( Figure 7E ), sometimes quite high.

Orifice. Secondary orifice roughly semicircular in non-ovicellate zooids, 0.10–0.13 mm long (average 50.107 mm, n 515, 3) by 0.14–0.19 mm wide (average 50.162 mm, n 515, 3), the distal margin a sharp, rounded rim.

Spines. Three to four orificial spines ( Figure 7C ), the proximal pair stout, cylindrical, erect; the median one or two spines shorter and more acute.

Avicularia. Lacking.

Ovicells. Ovicellate zooids in primary layer ( Figure 7D, E ) 0.38–0.68 mm long, including ovicell (average 50.556 mm, n 520, 3) by 0.18–0.38 mm wide (average 50.288 mm, n 515, 3); ovicell formed from two pairs of costae, the proximal pair heavy, often forming a blunt, sometimes bilobed mucro in midline, the distal pair completing the ovicell in a cap-like structure with two to four pores on top (often two are conspicuous). Frontally budded dwarf zooids ( Figure 7D, E ) occur in mature colonies, 0.25–0.34 mm long, including ovicell (average 50.294 mm, n 515, 3) by 0.19–0.23 mm wide (average 50.214 mm, n 515, 3). Dwarf zooid and ovicell roughly same size; zooidal shield with five to seven costae, the suboral pair thickened; two or three pores between adjacent costae. Ovicell has same form as that of ovicellate zooids in primary layer.

Ancestrula . One observed at Ketchikan ( Figure 7F ); 0.38 mm long by 0.23 mm wide; similar in form to subsequent autozooids, though in our specimen costae of ancestrula and several first- or second-generation zooids incompletely developed. Ancestrula with four orificial spines; first and second generations with two or three oral spines; seven periancestrular zooids (one distal, two distolateral, two proximolateral, two proximal).

Remarks

Cribrilina corbicula has not been reported since the original and subsequent descriptions from British Columbia ( O’Donoghue and O’Donoghue 1923, 1926), where it occurred on the seagrass Zostera marina . The one colony found at Ketchikan occurred on the alga Halosaccion glandiform e; C. corbicula thus seems to settle preferentially on plant and algal substrates, though our specimens from Sitka came from settling plates. O’Donoghue and O’Donoghue (1923) noted that C. corbicula is ‘‘a much larger form than C. annulata ’’; it is unclear what they meant by this, for colonies of C. annulata can become as large as those of C. corbicula , and zooids are about the same size. Perhaps C. corbicula simply appeared larger because of the coarser costae and larger intercostal pores. Cribrilina corbicula differs from C. annulata in colony colour (golden brown versus pinkish); zooids of C. corbicula are less firmly attached to one another and the colony is therefore rather flexible, which may be an adaptation to growing on vegetation. Zooids of C. corbicula tend to be narrower in proportion to length, and the raised, paddle-like suboral costae ( Figure 7E ) often seen in ovicellate zooids are not found in C. annulata .

We have examined the type specimen of C. corbicula (NHM 1963.12.30.43; locality labelled as ‘‘?Vancouver Island, O’Donoghue Collection’’), which consists of about 20 small colonies on both sides of two fragments of seagrass. Our specimens of C. corbicula are indistinguishable from the type in most characters. However, as with C. annulata , there seems to be intraspecific variation in life-history traits in C. corbicula . Although all the colonies in the type are young, no more than 6–7 mm in diameter, most of them have many ovicellate zooids in the primary layer, beginning as soon as the second generation of daughter zooids from the ancestrula. Our specimen from Ketchikan is of similar size, 6 mm across, but lacks ovicellate zooids altogether. O’Donoghue and O’Donoghue (1923) made no mention of frontally budded dwarf ovicellate zooids for C. corbicula , but we observed in the type material one fully formed dwarf zooid on one colony and one forming on another. In mature specimens from Sitka, ovicellate zooids are common in the primary layer, and dwarf zooids are abundant on some colonies. Therefore, presence or absence of dwarf zooids is not a distinguishing character between C. annulata and C. corbicula .

Distribution

The type locality of C. corbicula is Nanaimo , British Columbia ( O’Donoghue and O’Donoghue 1923) . In addition to the Ketchikan specimen, we have identified specimens from SERC settling plates from Dutch Harbour, Kodiak, Katchemak Bay , Port Valdez , and Sitka in Alaska , and from Puget Sound. Thus this is a boreal species apparently endemic to the north-eastern Pacific, with the known range extending from the eastern Aleutian Islands to Washington State .

Figures

Figure 7. (A, B) Cribrilina annulata (Fabricius): (A) autozooids and frontally budded dwarf ovicellate zooids; bleached; (B) autozooids (lower right), ovicellate zooids in primary layer (lower centre and left), and frontally budded dwarf ovicellate zooids (top); bleached. (C–F) Cribrilina corbicula (O’Donoghue and O’Donoghue): (C) astogenetically young autozooids; unbleached; (D) ovicellate zooids in primary layer and frontally budded dwarf ovicellate zooids; bleached; (E) ovicellate zooids in primary layer and newly forming dwarf ovicellate zooids with membranous front only (upper left of centre) or with incomplete costae (lower right and centre); note compressed, subspatulate suboral costae; unbleached; (F) ancestrula and surrounding zooids; unbleached. Scale bars: 500 Mm (A–E); 1 mm (F).