Family LOXOSOMATIDAE Hincks, 1880

Museums

Regional Maps

Introduction

After Wasson 2002
Loxosomatidae is the only family belonging to Order Solitaria — nevertheless, it is the largest natural grouping of kamptozoans, with about 100 of the 150 described species. Three loxosomatid genera are currently recognised (Loxosomella, Loxomespilon and Loxosoma) and are distinguished primarily by their basal attachment structures. About 20 species of loxosomatids have been reported from Australia and New Zealand, but only seven of them are described (see Wasson (2002) for distributions of undescribed species). Many more species certainly remain to be discovered, and until more thorough surveys are undertaken, it is impossible to assess the true diversity Australia's loxosomatids.

Loxosomatids, which form clonal aggregations by calycal budding, are considered the most plesiomorphic group of kamptozoans (Emschermann 1972). The highly contractile zooids are often very small (less than 1 mm high). Calyx and stalk are not sharply separated and longitudinal musculature is continuous between them. The calyx and tentacles are generally oriented obliquely to the stalk. The calyces are often compressed in the anterior-posterior axis, sometimes so strongly that the zooids resemble paddles.

Most loxosomatids dwell on other invertebrates. In Australia and New Zealand they have been reported from various sponges, a sipunculan, various polychaetes, two hirudineans, a squat lobster, two prawns, and various bryozoans (Wasson 2002). As more potential hosts in this region are examined for the presence of loxosomatid symbionts, this list will certainly grow. Each loxosomatid species appears to have either a single host species or a limited set of potential host species. Larvae, and possibly also buds and motile adults, can colonise new hosts; it is not known whether propagule preference or differential mortality on different host species is responsible for the observed distribution of adults. Association with other invertebrates has clear benefits for the loxosomatid. The zooids are often located in the pathway of the host's feeding or respiratory water currents, which they may use for their own ciliary feeding. The host probably offers the fragile zooids protection from predation or other damage. Whether the presence of loxosomatids negatively affects their hosts is not known.

Worldwide, many loxosomatid species (about 50%) live on polychaetes; they are found on or between the parapodia, on the gills, on the chaetae, or under the elytra of members of ten polychaete families. Loxosomella diopatricola Willams, 2000 and seven undescribed species of loxosomatids are known from polychaetes in Australia and New Zealand.

While loxosomatid species diversity is highest on polychaetes, loxosomatid density is probably highest on sponges. Loxosomatids may form strikingly dense aggregations on sponges — sometimes 100,000 zooids on a fist-sized sponge. Some of these sponge-dwelling forms are unusually darkly pigmented, and an aggregation against the background of a brightly coloured sponge can be eye-catching. Two undescribed species of Loxosomella are known from sponges in Australia and New Zealand.

General References

Emschermann, P. 1972. Loxokalypus socialis gen. et sp. nov. (Kamptozoa, Loxokalypodidae fam. nov.), ein neuer Kamptozoentyp aus dem nördlichen Pazifischen Ozean. Ein Vorschlag zur Neufassung der Kamptozoensystematik. Marine Biology, Berlin 12: 237-254

Nielsen, C. 1996. Three new species of Loxosoma (Entoprocta) from Phuket, Thailand with a review of the genus. Zoologica Scripta 25: 61-75

Wasson, K. 2002. A review of the invertebrate phylum Kamptozoa (Entoprocta) and synopsis of kamptozoan diversity in Australia and New Zealand. Transactions of the Royal Society of South Australia 126(1): 1-20

History of changes