Comparative studies on the statoblasts of higher phylactolaemate bryozoans

Abstract

Statoblasts of five higher phylactolaemates were compared morphologically. As a result, they were divided into two groups: Group I comprising Lophopus crystallinus, Lophopodella carteri, and Pectinatella gelatinosa, and Group II comprising Pectinatella magnifica and Cristatella mucedo. These two groups are thought to represent independent evolutionary series. In Group I and in P. magnifica, the statoblasts are curved to varying degrees after the manner of a saddle. When the dorsal and ventral valves are flattened, therefore, the contour is different between the two. In Group I, the outermost layer of a mature statoblast is hard-gelatinous and basophilic; it remains intact after the statoblast is set free. The statoblast does not float until it is dry, and the float is similar in size on both valves. In Group II, a mature statoblast is covered by a softgelatinous basophilic layer, which decays after the statoblast is released. The statoblast floats without drying, and the float is better developed on the dorsal valve than on the ventral. Moreover, in the members of Group II, large yolk granules are first formed, followed by much smaller yolk granules. When their statoblasts are treated with KOH, the shell is separated completely into two valves. These characters are common to many lower phylactolaemates. By contrast, in L. carteri and P. gelatinosa, the yolk granules are uniformly small and the capsule proper resists KOH treatment. On these points, L. crystallinus is somewhat different from these two species, suggesting its primitive nature.

Freshwater Bryozoa of Tonle Sap, Cambodia

“…Many of the phylactolaemate colonies collected in October (the end of the dry season) and from November to December (early in the wet season) were mature, and some of them also contained abundant statoblasts. The statoblasts of some species (e.g., Hyalinella punctata, Lophopodella carteri, Asajirella gelatinosa) need to dry before they can float (Mukai and Oda, 1980;Mukai, 1982Mukai, , 1984Wood and Marsh, 1996).…”

Statoblast ultrastructure and genetic identity ofPectinatella magnificapopulation, based on COI gene, from three different watersheds in Korea

“…The encapsulated dormant bud is widely used for species identification and is a prominent feature of the Phylactolaemata. Free statoblasts, resulting from asexual reproduction, are typically classified into three distinct forms: buoyant floatblasts, sessoblasts, and piptoblasts (Mukai & Oda 1980). P. magnifica forms floatblasts, which have a wide annulus of gas-filled chambers.…”

“…The capsule area and annulus were faintly reticulated (Figure 2c). According to Mukai and Oda (1980), mature statoblasts lying in the body cavity are covered with a thick gelatinous layer. We confirmed the existence of a transparent and sticky layer, which adhered tightly to the surface (Figure 2d).…”

Chromosomal heteromorphism in a Japanese population of Pectinatella gelatinosa and karyotypic comparison with some other phylactolaemate bryozoans

“…However, recent histological and histochemical studies (IVlukai & Oda, 1980a;1980b) indicate a closer relationship to Lophopodella carteri (Hyatt), which forms considerably smaller colonies, than to P. magnifica.…”

“…Most recent studies (Mukai, 1974;Mukai et al, 1979;Mukai & Oda, 1980a;1980b;Tazima et at., 1984) have utilized material collected at Tatara-numa, a shallow (maximum depth 2-3 m) 1 km 2 pond near Tatebayashi, Gunma Prefecture, about 68 km north of Tokyo, near or at the northernmost limit of the species in Japan. At this site large numbers of massive colonies can be observed in late summer and early autumn (Fig.…”