Parkermavella orientalis (Androsova and Gontar, 1982)

Grischenko, Andrei V., Dick, Matthew H. & Mawatari, Shunsuke F., 2007, Diversity and taxonomy of intertidal Bryozoa (Cheilostomata) at Akkeshi Bay, Hokkaido, Japan, Journal of Natural History 41 (17 - 20), pp. 1047-1161 : 1113-1115

Parkermavella orientalis (Androsova and Gontar in Gontar 1982), new combination

( Figure 26 ) Schizomavella auriculata orientalis Androsova and Gontar in Gontar 1982, p 549,

Figure 2-2 .

Material examined

ANC, colony on rock (NHM 2006.2.27.31), intact colony (NHM 2006.2.27.84); ACW, colony on rock (NHM 2006.2.27.83). Additional material: 38 specimens.

Description

Colony unilaminar, encrusting, coherent, forming circular patches up to 3 cm in diameter, bright beige or light orange in colour when alive. Zooids ( Figure 26A, B ) irregularly hexagonal, barrel-shaped, or rectangular, 0.35–0.53 mm long (0.42¡ 0.05 mm), 0.28– 0.45 mm wide (0.36¡ 0.04 mm), separated by fine suture lines between raised adjacent vertical walls. Frontal wall moderately convex to inflated; vitreous, smooth in young zooids, nodulose in mature zooids; imperforate centrally with five to nine conspicuous areolar pores along each lateral margin, separated by short ridges. Primary orifice ( Figure 26C ) subcircular, 0.10–0.13 mm long (0.11¡ 0.01 mm), 0.10–0.14 mm wide (0.12¡ 0.01 mm); proximal margin with shallow, U-shaped median sinus flanked by broad condylar shelves bearing blunt condyles. Newly budded zooids ( Figure 26A ) have one or two short, hollow ephemeral spines distal to primary orifice. Secondary orifice cormidial, formed proximally by sharp, elevated flanges of peristome extending from sides of suboral avicularian chamber to distal curvature formed by raised, thickened margin of succeeding zooid; circular in outline in immature zooids, transversely oval in ovicellate zooids; in mature zooids, lateral flanges connect with proximolateral corners of ovicell. Immediately proximal to orificial sinus is a small suboral avicularium ( Figure 26B ) with complete cross-bar and semicircular mandible directed proximally at an angle to frontal plane; avicularian chamber narrow, crescentic, prominent in immature zooids, becoming immersed and covered by nodules in ovicellate zooids, flanked by a pair of small pores. Ovicellate zooids additionally have paired lateral oral avicularia ( Figure 26D, E ) directed proximolaterally at an angle to frontal plane, somewhat larger than median avicularium, with complete cross-bar; mandible subspatulate, slightly elongate; rostral opesia triangular distal to cross-bar; lateral avicularia occasionally single or lacking altogether; rarely only one or two lateral avicularia present, with median suboral avicularium absent. Ovicell ( Figure 26D, E ) hemispherical, recumbent on following zooid, broad, 0.18–0.25 mm long (0.21¡ 0.02 mm), 0.22–0.27 mm wide (0.25¡ 0.01 mm); with concave proximal margin; smooth on top, perforated with 25–30 irregular pores; with age, covered around periphery with heavy nodular secondary calcification. Zooids intercommunicate via uniporous septula. Ancestrula ( Figure 26F ) similar in form to autozooid, reduced in size, 0.27 mm long, 0.20 mm wide, irregularly hexagonal, with quite convex frontal wall and raised vertical walls; orifice circular, 0.08 mm long, 0.08 mm wide; surrounded by seven zooids.

Remarks

Gordon and d’Hondt (1997) established the genus Parkermavella for Schizomavella -like species that differ from Schizomavella in having an imperforate frontal shield and only marginal areolae. Characters of Parkermavella include a proximal oral sinus; articulated oral spines distally; one or more adventitious avicularia near the orifice or elsewhere on the frontal surface; and a prominent or subimmersed ovicell with smooth ectooecial calcification, many perforations that may be rimmed, and secondary calcification sometimes encroaching around the distal margin. The species of Androsova and Gontar treated here lacks frontal perforation and has most of the other characters of Parkermavella , and therefore belongs in that genus.

Gontar (1982) originally described this species as subspecies orientalis of Schizomavella auriculata ( Hassall, 1842) . However, the nominal subspecies never has more than a single median avicularium associated with the orifice, and also differs in orifice shape and in having numerous frontal pores; it is distributed in the northeastern Atlantic from Scotland to Gibraltar ( Hayward and Ryland 1999). On the basis of these differences in morphology and range, we here elevate Gontar’s subspecies to species rank as P. orientalis (Androsova and Gontar, 1982) .

Parkermavella orientalis is very similar to S. triavicularia Soule, Soule, and Chaney, 1995 , described from the Santa Barbara Channel, which likewise has a single median suboral avicularium in non-ovicellate zooids and an additional pair of lateral oral avicularia in ovicellate zooids. Parkermavella orientalis differs from the latter in several characters: (1) it lacks frontal pores, with well-developed areolar pores instead; (2) developing zooids near the colony margin have one or two ephemeral distal oral spines, whereas S. triavicularia has three spines; (3) the median suboral avicularium is closer to the suboral sinus than in S. triavicularia ; and (4) ovicellate zooids have dimorphic suboral avicularia, with the lateral avicularia larger than the median one, and with more elongate mandibles; the median and lateral avicularia are similar in size and form in mature zooids of S. triavicularia .

The remarkable overall similarity of S. triavicularia and P. orientalis dispels misgivings one might have in accepting genera with and genera without a perforate frontal shield in the same family. Schizomavella triavicularia , which is evenly perforated, is otherwise so similar to S. orientalis , which is not, that there is little doubt the two are closely related; the similarity extends to both species having a pair of small pores flanking the avicularian chamber. Although convergence is a possibility, we conclude that the secondary loss of frontal perforation in Parkermavella is a more likely explanation. The small pores that flank the avicularian chamber are actually primary perforations in the frontal shield, as indicated by their presence in the forming shield in marginal zooids ( Figure 26A ), and in this sense, the frontal pores can be viewed as having been severely reduced in number, rather than lost entirely.

Distribution

This species was originally described from Crabovaya Bay, Shikotan Island, Kuril Islands, and also recorded from Zelenyy Island, Habomai Islands (Small Kuril Achipelago). Akkeshi Bay is the third known locality.

Figures

Figure 2. Dendrogram (below) showing similarity of sampling localities based on species presence/absence, and a map (above) showing the geographical distribution of three groups of sampling localities (circled) that are less than 70% similar in species composition between groups.

Figure 26. Parkermavella orientalis (Androsova and Gontar in Gontar 1982). (A) NHM 2006.2.27.31; (B–E) NHM 2006.2.27.84; (F) NHM 2006.2.27.83. (A) Colony margin with developing zooids; (B) immature zooids; (C) orifice of immature zooid, showing condyles and suboral avicularium; (D) group of mature zooids with ovicells, showing variability in positions of oral avicularia; (E) mature zooids with three oral avicularia; (F) ancestrular region. Scale bars: 0.5 mm (A, B, D–F); 0.1 mm (C).