Moerisia Boulenger, 1908

Calder, Dale R., 2010, Some anthoathecate hydroids and limnopolyps (Cnidaria, Hydrozoa) from the Hawaiian archipelago 2590, Zootaxa 2590 (1), pp. 1-91 : 57

Genus Moerisia Boulenger, 1908

Moerisia Boulenger, 1908: 358 .

Type species. Moerisia lyonsi Boulenger, 1908 , by monotypy.

Diagnosis. Moerisiid hydroids with moniliform, hollow tentacles.

Moerisiid medusae with moniliform tentacles; gonads smooth, forming a continuous mass extending from central manubrium to manubrial lobes.

Remarks. The brackish-water genus Moerisia Boulenger, 1908 as presently constituted is widespread and relatively familiar, but most nominal species assigned to it are poorly understood taxonomically. In the Indo-west Pacific region, only the species currently known as Moerisia horii ( Uchida & Uchida, 1929) has been thoroughly studied in all phases of its life cycle. Nevertheless, relationships of that species to M. gemmata ( Ritchie, 1915) and M. gangetica Kramp, 1958 , both described from the same general region of India, or to other nominal species currently assigned to the genus ( Moerisia lyonsi Boulenger, 1908 , Caspionema pallasi Derzhavin, 1912 , Moerisia inkermanica Paltschikowa-Ostroumowa, 1925 , Moerisia alberti Leloup, 1938 , and Moerisia carine Bouillon, 1978b ), have not been adequately explored. Moreover, a number of moerisiid records worldwide attributed to M. lyonsi , including accounts of mine ( Calder 1971; Calder & Burrell 1967; Sandifer et al. 1974), have been based on adult medusae with numerous (>20) marginal tentacles. As originally described by Boulenger (1908), however, mature medusae of that species normally have four tentacles. Rees & Gershwin (2000), working with Moerisia sp. from California, believed that only one or two morphologically variable species may prove to exist in Moerisiidae Poche, 1914 . Confusion and uncertainty prevails in the taxonomy of the genus at present, and a revision of Moerisia and its species is needed. As for M. gemmata, Rees & Thursfield (1965) included it in the synonymy of M. inkermanica (as Ostroumovia inkermanica ).

Although restricted to environments of low salinity, species of Moerisia are well-known to be invasive ( Purcell et al. 1999; Rees & Gershwin 2000; Ma & Purcell 2005a, b). Notably, resistant podocysts are known to occur in the life cycle, and may facilitate dispersal of these hydrozoans.

Fewer than 10 species are currently included in the genus Moerisia ( Bouillon et al. 2006; Schuchert 2009). One of these, M. horii , has been reported from Hawaiian waters ( Cooke 1977).