Microporella germana Dick and Ross, 1988

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 : 3758-3763

Microporella germana Dick and Ross, 1988

( Figure 21A–D)

Microporella germana Dick and Ross 1988, p 74 , Plate 12A, B.

Microporella ciliata: Dick and Ross 1986, p 89 (in part);? Kluge, 1975, p 629, Figure 361.

Description

Colony. Unilaminar, forming tightly encrusting, circular or irregular colonies on rocks, shells, and serpulid tubes; off-white in colour; covered with glistening ectocyst when alive; largest observed 2.2 cm across.

Zooids. Roughly hexagonal or oval, distinct at all stages, separated by a shallow groove; 0.43–0.73 mm long (average 50.556 mm, n 520, 4) by 0.25–0.43 mm wide (average 50.366 mm, n 520, 4).

Frontal wall. Moderately convex, granular, often with a small, blunt umbo immediately proximal to ascopore; six to eight areolar pores along each lateral margin; frontal wall uniformly perforated with smaller pores over entire surface; pore openings can become enlarged as frontal wall thickens.

Ascopore ( Figure 21B, C). Small, wider than long; separated from proximal margin of orifice by a distance less than or equal to ascopore width; surrounded by a zone of smooth calcification that often extends on to distal surface of umbo; distal ascopore margin with an irregular or club-shaped median projection ending in sharp denticles; rest of margin with sharp denticles that sometimes connect with median projection by thin rays.

Orifice ( Figure 21B). Semicircular, broader than long, 0.07–0.11 mm long (average 50.086 mm, n 520, 4) by 0.10–0.15 mm wide (average 50.119 mm, n 520, 4); proximal margin straight, serrated, with a blunt-triangular condylar shelf at each corner.

Spines ( Figure 21A, B). Marginal zooids with four to six erect spines around distal margin of orifice (frequencies: four543%, five552%, six55%; n 542, 3); spine scars often evident on other non-ovicellate zooids.

Avicularia ( Figure 21A, D). Zero to two per zooid (frequencies: zero52%, one570%, two528%; n 583, 3), located lateral or proximolateral to ascopore, often close to orifice, pointing distolaterally; if paired, one usually points at a slightly different angle from the other relative to long axis of zooid. Rostrum raised, mandible long-triangular, with setose tip about as long as mandible proper.

Ovicell ( Figure 21D). Globose, 0.18–0.33 mm long (average 50.239 mm, n 515, 3) by 0.20–0.33 mm wide (average 50.265 mm, n 515, 3); partly immersed in frontal wall of succeeding zooid; surface granular like frontal wall and confluent with frontal wall of succeeding zooid; coarse ribs variably developed around margin, extending toward centre; scattered minute pores around periphery between ribs; central area imperforate except for occasional isolated pores.

Ancestrula . Not observed.

Remarks

Specimens at Ketchikan are very similar in zooidal measurements, morphology, and avicularium frequencies to material from Kodiak , Alaska, the type locality ( Dick and Ross 1988). The only noteworthy difference is in spine frequencies: zooids in the Kodiak population have three to five spines, with the modal number four; those at Ketchikan have four to six spines, with the modal number five .

At East Tongass Narrows, we collected a colony of Microporella (here termed Microporella form A ( Figure 21E–H), growing on a large serpulid worm tube, that has a few zooids in the interior of the colony with three avicularia per zooid ( Figure 21E): one lateral to the ascopore and angled distolaterally; the second on the same side proximal to the first and angled distolaterally or laterally; and the third on the opposite side lateral to the ascopore, angled distolaterally. Other zooids have only two avicularia, but both on the same side ( Figure 21F). In addition, some zooids have exceptionally heavy suboral umbones ( Figure 21F), and the ovicells are umbonate ( Figure 21E, F). This specimen is unusual, because autozooids with two frontal avicularia on the same side are quite rare in Microporella . In their overview of this genus, Taylor and Mawatari (2005) observed only two cases of an autozooid with this condition among all the material they examined, and one of these cases resulted from reparative growth of a damaged frontal shield.

We consider this specimen to be an aberrant, perhaps mutant form, and in any case hesitate to describe it as a distinct species without more material. In many respects, it has an admixture of characters occurring in M. germana and M. ketchikanensis , and we suggest the possibility that it might be a hybrid between the two. Observations that support this idea are as follows: (1) Zooids at the growing margin have zero to two avicularia; when two are present, they are on opposite sides in the normal fashion and are angled in slightly different directions, as is typical for M. germana ; however, they also tend to be situated somewhat more proximally than is typical for that species, but more typical of M. ketchikanensis . (2) The colony has a mixture of ascopore types, some like M. germana ( Figure 21G), some like M. ketchikanensis ( Figure 21H), and some of intermediate form. (3) Zooids have four (80%) or five (20%) distal spines, frequencies more similar to M. germana (95% of zooids have four or five spines) than to M. ketchikanensis (80% of zooids have three or four spines). However, modal spine number is four (mode in M. ketchikanensis ) rather than five (mode in M. germana ). (4) A prominent umbo proximal to the ascopore and on the ovicell are more characteristic of M. ketchikanensis than of M. germana . (5) The occurrence of two avicularia on the same side may be viewed as a superposition of developmental information of M. germana and M. ketchikanensis involved in producing avicularia. Roughly 98% of zooids of M. germana produce one or two avicularia; 83% of zooids of M. ketchikanensis produce one avicularium. Combination of a developmental signal to produce an avicularium on each side lateral to the ascopore ( M. germana ) with that to produce a single avicularium farther proximally on one side ( M. ketchikanensis ) would give the observed pattern of two avicularia on one side and one on the other. Similarly, combination of a developmental signal to produce a single avicularium on one side ( M. germana ) with that to produce a single avicularium farther back on the same side ( M. ketchikanensis ) would give the observed pattern of two avicularia on the same side. This type of superposition should also produce zooids with four avicularia (two on each side); however, as only 0.5% of zooids of M. ketchikanensis have two avicularia, this would be a rare event.

Distribution

The known range of M. germana extends from Ketchikan (present study) around the Gulf of Alaska and Alaska Peninsula to Dutch Harbour, Alaska ( Dick and Ross 1988).

Genus Fenestrulina Jullien, 1888 Fenestrulina delicia Winston, Hayward, and Craig, 2000

( Figure 22A–D )

Fenestrulina delicia Winston, Hayward, and Craig 2000, p 417 , Figures 13–15 .

Description

Colony. Unilaminar, encrusting, forming small, whitish, circular patches; material examined comprised ovicellate colonies, 0.5 cm in diameter.

Zooids. Rounded-hexagonal to oval, often irregular, varying considerably in size and shape, 0.53–0.78 mm long (average 50.619 mm, n 515, 3) by 0.28–0.45 mm wide (average 50.348 mm, n 515, 3); with smooth lateral walls sloping inward, leaving a deep fissure between some zooids, the margin of the lateral gymnocyst forming a sharp border with frontal wall, sometimes encroaching onto it.

Frontal wall. Smooth, slightly inflated, highest at or slightly proximal to ascopore, with large stellate pores in two to three rows between ascopore and orifice, one or two rows along lateral margins, and one row along proximal margin; asymmetrical zooids may have up to four rows along one of the lateral margins; frontal wall imperforate in the area between ascopore and proximal zooidal margin.

Orifice ( Figure 22A ). Semicircular, usually wider than long, 0.10–0.13 mm long (average 50.116 mm, n 515, 4) by 0.11–0.16 mm wide (average 50.138 mm, n 515, 4); proximal margin straight and smooth, with a minute triangular condyle present near corner on each side; orifice subterminal, with a row of stellate pores distal to orifice, visible in a single transverse panel or a pair of panels sharply delineated by a border of smooth calcification.

Ascopore ( Figure 22C ). Separated from orifice by 2.5–3.5 ascopore widths; surrounded by a slightly raised border; irregular in size and shape, blunt V-shaped to U-shaped, 0.05– 0.08 mm wide; both proximally directed tabula and proximal margin deeply serrated, with irregularly branched processes terminating in tiny points; fractal in appearance.

Spines. Non-ovicellate zooids with one to four orificial spines, but most frequently with a single spine scar evident in midline ( Figure 22A ); ovicellate zooids with a short spine on each side lateral to orifice, outside proximolateral margins of ovicell ( Figure 22B ).

Ovicell ( Figure 22A, B ). Raised, hemispherical, conspicuous; narrower than zooid width, usually longer than broad, 0.28–0.35 mm long (average 50.316 mm; n 515, 3) by 0.23–0.30 mm wide (average 50.264 mm, n 515, 3); with a raised border and large pores around margin; distal three-fifths coarsely rugose with thick ribs running between marginal pores to top, where they merge with an irregular transverse fold; sometimes with two to three slit-like pores on top between ribs; proximal to transverse fold, ovicell is narrower and smooth, extending part-way along each side of orifice. Older ovicells can become entirely rugose, with a smooth, raised lip along the proximal margin. Operculum fits to opening of secondary orifice formed by ovicell margin, and can cover either primary or secondary orifice.

Avicularia. Lacking.

Ancestrula ( Figure 22D ). Tatiform, with 10 spines around opesial margin, surrounded by six periancestrular zooids (one distal, two distolateral, two proximolateral, one proximal).

Remarks

Although we did not find this species intertidally at Ketchikan, it occurred on SERC settling plates at Sitka, Alaska; we include it here to eliminate potential confusion with the two species of Fenestruloides that occurred intertidally at Ketchikan. Fenestrulina delicia was first recognized ( Craig 1994) and described ( Winston et al. 2000) only recently from the Gulf of Maine. Our specimens agree in virtually all characters with Atlantic F. delicia , e.g. the ovicell strongly ribbed distally and smooth proximally; a pair of spines flanking the proximolateral corners of the ovicell; some zooids with only a single median distal spine; the smooth, sloping vertical walls forming a sharp border with the frontal surface; bordered panels distal to the orifice; and a tatiform ancestrula.

Fenestrulina delicia is very similar to F. sinica Liu, Yin, and Ma, 2001 . Indeed, we would consider them synonymous, except that the ancestrula of F. sinica was described as resembling later autozooids, whereas that of F. delicia is tatiform. Fenestrulina delicia also resembles F. farnsworthi Soule, Soule, and Chaney, 1995 , which has a tatiform ancestrula (12 spines) and zooids with a sharp border between the smooth vertical walls and frontal wall. However, F. farnsworthi has much smaller zooids, only one or two rows of pores between ascopore and orifice, a mostly imperforate frontal wall, and five to seven long distal spines.

The recent, nearly contemporaneous discovery of F. delicia in boreal waters of the western Atlantic and eastern Pacific suggests it might be a species introduced to one or both of these regions within the past few decades. Alternatively, occurrence of a similar species ( F. sinica ) in China and a morphologically similar population of uncertain identity that we have found at Akkeshi, Japan might indicate that F. delicia and F. sinica belong to a species complex in the northern Hemisphere that has previously gone undetected due to misidentification as Fenestrulina malusii ( Audouin 1826) , a species until recently regarded as cosmopolitan (see discussion in Soule et al. 1995, p 156).

Distribution

Fenestrulina delicia is a boreal species known from Maine in the north-western Atlantic, and from the northern Gulf of Alaska to San Francisco, California in the Pacific. We have identified specimens on SERC settling plates from Valdez and Sitka , Alaska ; Coos Bay , Oregon ; and San Francisco .

Figures

Figure 13. Porella columbiana O’Donoghue and O’Donoghue, paralectotype, BMNH 1964.1.2.15; bleached: (A) group of autozooids; (B) zooids near colony margin showing stages in formation of suboral avicularian chamber; (C) group of ovicellate zooids; (D) enlargement of autozooidal orifice showing condyles and weak lyrula. Scale bars: 500 Mm (A–C); 200 Mm (D).

Figure 22. Fenestrulina delicia Winston, Hayward, and Craig; subtidal specimens from Sitka, Alaska: (A) two complete autozooids and part of an ovicell; lightly bleached for cleaning; (B) group of ovicellate zooids; lightly bleached for cleaning; (C) enlargement of ascopore from zooid at right in Figure 22A above; (D) tatiform ancestrula and periancestrular zooids; unbleached. Scale bars: 500 Mm (A, B, D); 50 Mm (C).