Notes on astogeny of some Petraliellidae (Bryozoa) from Australia

Abstract

Members of the bryozoan family Petraliellidae share the capacity to develop basal rhizoids, which anchor the unilaminar, semi-repent parts of the colonies above the substratum, and enable them to overgrow other, competing sessile forms. Little is known of the larval behaviour and settlement, or the early astogeny of species. Ancestrulate colonies of the Australian Tertiary lunulitiform species Smittia biincisa are referred to the genus Riscodopa, and together with Riscodopa paucipora sp. nov. are described and compared with the Recent species R. cotyla and R. parva from New Zealand, and with R. hyalina sp. nov. from New South Wales, Australia. All the Recent species are known to develop basal rhizoids, and an early astogeny similar to that of many other small, rooted bryozoans, comprising the post-metamorphosis development of a binary complex, including rhizoid and feeding elements, is inferred for Riscodopa. Observations on living Hippopetraliella magna from Queensland suggest that both the ancestrular morphology and early astogeny show a capacity for semi-repent growth, even though they do not include rhizoid development. Larvae metamorphose without direct attachment, and the ancestrula develops elongated, partially calci ed supporting processes, which raise the early stages of growth above the substratum. A similar kind of ancestrula has been found in preserved specimens of Mucropetraliella ellerii.

Petraliellidae Harmer, 1957 (Bryozoa: Cheilostomata) from Queensland, Australia

“…This is later covered by a lamina emanating from one of the proximal septular pores. Cook & Bock (2002) also noted the large size of colonies found as strand-line debris from near Townsville. The release of larvae, settlement and early astogeny has been described by Cook & Bock (2002), and the ancestrula resembles that of Mucropetraliella ellerii (MacGillivray, 1869) in having uncalcified prolongations which raise it above the substratum, to which it is only intermittently attached.…”

“…Canu & Bassler (1929) described the ovicells as 'broken ', and Harmer (1957) as 'due to a defective condition in the ovary'. The release of larvae, settlement and early astogeny has been described by Cook & Bock (2002), and the ancestrula resembles that of Mucropetraliella ellerii (MacGillivray, 1869) in having uncalcified prolongations which raise it above the substratum, to which it is only intermittently attached. This is later covered by a lamina emanating from one of the proximal septular pores.…”

“…Apparent delay in the completion of the ovicell during ontogeny is frequent in the Petraliellidae (Bock, 1982;Cook & Bock, 2002), but is particularly noticeable in Petraliella magna. Canu & Bassler (1929) described the ovicells as 'broken ', and Harmer (1957) as 'due to a defective condition in the ovary'.…”

New distribution records of the Arctic bryozoan Uschakovia gorbunovi Kluge, 1946 in the Barents and Greenland Seas

“…Information regarding the distribution and spatial patterns of biodiversity, both for benthic organisms in general and specifically for bryozoans, is important for monitoring long-term changes in the marine environment and mitigating anthropogenic impacts on the ocean (Cusson et al, 2007;Cook et al, 2018). The most comprehensive source for the diversity and distribution of Arctic bryozoans is a monograph by Kluge, originally published in Russian in 1962, and later translated into English and republished in 1975(Kluge, 1962, 1975.…”