The Biological Bulletin, Vol 184, Issue 2 153-185, Copyright © 1993 by Marine Biological Laboratory

ECOLOGY, EVOLUTION AND BEHAVIOR

On Antarcrtic Entoprocta: Nematocyst-like Organs in a Loxosomatid, Adaptive Developmental Strategies, Host Specificity, and Bipolar Occurrence of Species

P. Emschermann
Fakultat far Biologie der Universitat Freiburg i.Br., Biologie far Mediziner, Schanzlestrasse 1, 7800 Freiburg i.Br. BRD

In the southern Weddell Sea and the Bransfield Strait a total of eight species of entoprocts were found: four Loxosomatidae, originally known to be common in the Northern Polar Sea and the Atlantic sector of the subarctic region (Loxosomella antedonis Mortensen, 1911, L. compressa Nielsen and Ryland, 1961, L. varians Nielsen, 1964, and L. antarctica Franzen, 1973); three new species of loxosomatids (L. brochobola spec. nov., L. seiryoini spec. nov., and L. tonsoria spec. nov.); and one single colonial entoproct Barentsia discreta (Busk, 1886) which is distributed worldwide. Loxosomella brachystipes, described by Franzen in 1973 from South Georgia, is shown to be synonymous with L. varians Nielsen, 1964. The microscopic investigation of the above species revealed several morphological characters, previously unknown, that add to our knowledge of the Entoprocta in general, and also help in characterizing species. The first of these novel characters, observed in L. brochobola spec. nov., are extruding organs similar to cnidarian spirocysts. This is the first description of such organs in entoprocts. Loxosomella antarctica is capable of calyx regeneration and thereby becomes the only solitary entoproct known to have such a regeneration capacity. Finally, the formation of special resting buds in Barentsia discreta is described. The range of morphological variation of these species, the question of host specificity in the Loxosomatidae, and the bipolar occurrence of some of these species is discussed.