Petraliellidae

Belongs within: Lepraliomorpha.

Bryozoans get rooted

Published 11 September 2022

Life as a sessile organism comes with its challenges. Whereas your mobile compatriots have the option to change their surroundings if conditions become difficult, you need to weather things as they come. You need a firm, broad foundation to achieve optimum growth. You need to fend off competitors attempting to occupy the same space. The Petraliellidae are one group of bryozoans who have these challenges covered.

Petraliellids are found in tropical and subtropical waters at a range of depths from the sublittoral to the deep sea. Colonies include large feeding zooids with evenly perforate frontal walls. Avicularia with robust, hooked, serrated mandibles are often present alongside the opercular openings. Eggs and larvae are brooded in globular, finely porous ovicells that develop at the front of the maternal zooids (Cook & Chimonides 1981; Tilbrook & Cook 2005). In life, colonies are brilliantly coloured due to pigments in the soft tissues of the zooids.

Colonies of petraliellids can vary significantly in overall form, with examples of a single species potentially differing in habit due to environmental conditions of stage of development. Habit can vary from encrusting to semi-erect or lunulitiform (lens-shaped). They are able to develop the last two forms due to the production of rhizoids, elongate root-like structures (formed from modified non-feeding zooids) that emerge from openings in the basal plate of the colony and anchor it to the underlying substrate. Semi-erect colonies may be unilaminar, bilaminar or tubular (‘bilaminar’ presumably refers to two layers of zooids growing back to back, one above and one below).

Production of rhizoids allows petraliellid colonies to establish themselves on unstable substrates such as sand beds or rubble, anchoring the colony in place and lifting it above the substrate surface. The capacity for raised growth also allows the colony to potentially overgrow competitors such as sponges. For encrusting bryozoans, sponges and the like may present a significant limitation to colony growth, but petraliellids are capable of turning the tables.

Systematics of Petraliellidae

Petraliellidae
    |--Sinupetraliella Stach 1936THG01
    |    `--*S. litoralis (Hastings 1932)TC05 [=Petralia litoralisTC05, Petraliella litoralisTHG01]
    |--Mucropetraliella Stach 1936THG01 [incl. Poripetraliella Harmer 1957TC05]
    |    |--*M. ellerii (MacGillivray 1869) [=Lepralia ellerii]THG01
    |    |--M. asymmetrica Hayward & Cook 1983TC05
    |    |--M. bennetti (Livingstone 1926) [=Petralia vultur var. bennetti]TC05
    |    |--M. capricornensis Tilbrook, Hayward & Gordon 2001THG01
    |    |--M. falcifera (Canu & Bassler 1929)THG01
    |    |--M. loculifera Harmer 1957THG01
    |    |--M. magnifica (Busk 1884)THG01
    |    |--M. neozelanica (Livingstone 1929)TC05
    |    |--M. philippinensis (Canu & Bassler 1929)THG01 (see below for synonymy)
    |    |--M. serrata (Livingstone 1926) [=Petralia vultur var. serrata]TC05
    |    |--M. thenardii (Audouin 1826)TC05
    |    |--M. tuberosa (Busk 1884) [=Lepralia tuberosa, M. (*Poripetraliella) tuberosa]TC05
    |    `--M. vultur (Hincks 1882)TC05
    `--Petraliella Canu & Bassler 1927 [incl. Hippopetraliella Stach 1936, Serripetraliella Stach 1936]TC05
         |--*P. bisinuata (Smitt 1873) [=Escharella bisinuata, Mucronella bisinuata]TC05
         |--P. buski Stach 1936 [incl. P. arafurensis Stach 1936]TC05
         |--P. concinna (Hincks 1891) [=Schizoporella concinna, Hippopetraliella concinna]TC05
         |--P. crassocirca Canu & Bassler 1929 (see below for synonymy)TC05
         |--P. dentilabris (Ortmann 1892) (see below for synonymy)TC05
         |--P. dorsiporosa (Busk 1884) (see below for synonymy)TC05
         |--P. firmata (Waters 1887) [=Mucronella firmata]UB72
         |--P. magna (d’Orbigny 1852) (see below for synonymy)TC05
         `--P. marginata (Canu & Bassler 1928) [=Hippopetraliella (Serripetraliella) marginata]TC05

Mucropetraliella philippinensis (Canu & Bassler 1929)^THG01 [=Petraliella philippinensis^TC05; incl. P. falcifera Canu & Bassler 1929^TC05]

Petraliella crassocirca Canu & Bassler 1929 [=Hippopetraliella crassocirca; incl. Cheiloporina campanula Hayward & Ryland 1995, Lepralia crassa Thornely 1912 non Reuss 1874]^TC05

Petraliella dentilabris (Ortmann 1892) [=Lepralia dentilabris; incl. Petralia chuakensis Waters 1913, Hippopetraliella (*Serripetraliella) chuakensis, Petraliella chuakensis, Hippopetraliella (Serripetraliella) chuakensis hastingsae Stach 1936]^TC05

Petraliella dorsiporosa (Busk 1884) [=Lepralia dorsiporosa, *Hippopetraliella dorsiporosa; incl. Mucropetraliella valdemunita Harmer 1957]^TC05

Petraliella magna (d’Orbigny 1852) [=Semieschara magna, Hippopetraliella magna; incl. Petralia gigas Hincks 1885, Lepralia japonica Busk 1884, Petralia japonica]^TC05

*Type species of generic name indicated

References

Cook, P. L., & P. J. Chimonides. 1981. Morphology and systematics of some rooted cheilostome Bryozoa. Journal of Natural History 15 (1): 97–134.

[TC05] Tilbrook, K. J., & P. L. Cook. 2005. Petraliellidae Harmer, 1957 (Bryozoa: Cheilostomata) from Queensland, Australia. Systematics and Biodiversity 2 (3): 319–339.

[THG01] Tilbrook, K. J., P. J. Hayward & D. P. Gordon. 2001. Cheilostomatous Bryozoa from Vanuatu. Zoological Journal of the Linnean Society 131: 35–109.

[UB72] Uttley, G. H., & J. S. Bullivant. 1972. Biological results of the Chatham Islands 1954 expedition. Part 7: Bryozoa Cheilostomata. New Zealand Department of Scientific and Industrial Research Bulletin 139: 1–61.