194 



TITGEN 



appearance. They were found because Tomlinson (1973) 

 intentionally looked for their burrows in mollusk shells. 



ACROTHORACICA 



Acrothoracicans are small, nonparasitic naked barna- 

 cles that burrow primarily in calcareous substrata. These 

 substrata include live coral, coral rock, and mollusk shells. 

 Sexes are separate, and the burrows are created by the 

 females. The dwarf males are short-lived, non-feeding 

 organisms (Tomlinson, 1969) that are usually found near 

 the attachment disc of the female. 



Newman and Tomlinson (1974) presented an interest- 

 ing question on the dispersal mechanisms of acrothoracican 

 barnacles. The adults are poor dispersers because they arc 

 obligate inhabitants of calcium carbonate. Therefore, it is 

 difficult to explain the distribution of species such as 

 Lithogliiptes bicornis Aurivillius, 1892, which is found in 

 the Caribbean Sea, the Red Sea, Australia, Japan, the 

 Marshall Islands, and the Line Islands. The difficulty arises 

 because the naupliar dispersal stages are usually passed in 

 the egg, and the cyprids are non-feeding and weak swim- 

 mers (Newman and Tomlinson, 1974). 



A single paper has been published reporting on 

 acrothoracicans from Enewetak Atoll (Tomlinson, 1973). 

 Not collected as barnacle material, the specimens were 

 discovered in shells of the turbinid snail Turbo argi;ro- 

 stomus Linnaeus, 1758, housed at the U. S. National 

 Museum of Natural History's Division of Malacology. 



The three species of acrothoracican barnacles reported 

 from Enewetak Atoll have relatively wide distributions con- 

 sidering their presumed limited powers of dispersal. 

 Cr\jptophialus heterodontus Tomlinson, 1969, has a 

 western Pacific distribution and is known from Australia, 

 the Marshall Islands (Tomlinson, 1969), and Okinawa 

 (Tomlinson, 1973). Lithogli;ptes mitis Tomlinson, 1969, 

 appears to have an insular distribution, having been col- 

 lected at Fiji (Tomlinson, 1969), the Loyalty Islands, the 

 Me^I:shall Islands, New Caledonia, Ninafou Island 

 {?Niuafou), and Samoa (Tomlinson, 1973). As mentioned, 

 Uthoglt;ptes bicornis Aurivillius, 1892, has an unusually 

 wide distribution for an acrothoracican barnacle. Over part 

 of its rarige it is known by its synonyms Lithogl\;ptes spi- 

 natus Tomlinson and Newman, 1960, and Lithoglf^ptes 

 ampulla Aurivillius, 1892 (Newman and Tomlinson, 1974). 



Only a few species of acrothoracicans have been 

 reported from the Marshall, Caroline, and Gilbert Islands 

 (Tomlinson, 1969, 1973) that have not also been found at 

 Enewetak Atoll. Due to the cryptic habitat of burrowing 

 barnacles and the fact that ihey are seldom looked for, it 

 is probable that these and/or other acrothoracicans occur 

 at Enewetak Atoll. 



RHIZOCEPHALA 



Rhizocephalans are endoparasites of crustaceans, pri- 

 marily decapods. The acjiults are highly modified and bear 

 no resemblance to other cirripeds. However, they are clas- 



sified with barnacles because their naupliar larvae have the 

 characteristic frontolateral horns, and there is a typical 

 cyprid larval stage. 



There are no published accounts of rhizocephalans 

 from Enewetak Atoll or the Marshall Islands. The only 

 record is of a sacculinid found on a male specimen of 

 Galathea affinis Ortmann, 1892, collected at Sta. No. 

 JWK-412, Engebi Island, Enewetak Atoll, found on an 

 Acropora sp. (Haig, personal communication). Apparently, 

 no other rhizocephalans were found on the decapods col- 

 lected at Enewetak Atoll (J. S. Garth and A. J. Bruce, per- 

 sonal communication). However, Sacculina punctata 

 Boschma, 1934, and Sacculina bipunctata Kossmann, 

 1872, have been reported from the Caroline Islands. 

 Sacculina carpiliae Guerin-Ganivet, 1911, Sacculina incon- 

 stans Boschma, 1952, and possibly Sacculina actaeae 

 Guerin-Ganivet, 1911, have been reported from the Gilbert 

 Islands (Boschma, 1953, 1955); and an undescribed 

 species of Lernaeodiscus has been reported from Hawaii 

 (Edmondson, 1946; Boschma, 1953). Although present 

 records indicate that infection by rhizocephalans at 

 Enewetak Atoll is of low incidence, some undoubtedly 

 occurs. In general, little work has been done on rhizo- 

 cephalans in recent years, probably because of the histo- 

 logical work necessary for taxonomic identification. 



DISCUSSION 



The most noticeable aspect of barnacle research at 

 Enewetak Atoll, and the Marshall Islands in general, is the 

 paucity of work that has been done. The more obvious 

 noncommensal forms have been collected and identified, 

 along with a few of the more cryptic species. However, in 

 comparison to the Caroline Islands, the smaller commensal, 

 burrowing, and parasitic forms have been largely missed. 

 This is characteristic of studies in which barnacle research 

 is incidental to other work being carried out. 



Because the cirriped fauna of Enewetak Atoll is so 

 poorly known, little can be said of its biogeography. Its 

 fauna, however, is Indo-West Pacific in origin, with some 

 elements of the circumtropical-temperatc fauna. Enewetak 

 Atoll is composed of low islands and is located on the 

 Pacific Plate. For these reasons the fauna can be expected 

 to be less diverse than at high islands, such as the Caro- 

 lines, or islands such as Palau and the Philippines that are 

 not on the Pacific Plate (Springer, 1982; W. A. Newman, 

 personal communication). While some patchiness is to be 

 expected, the low islands of the Marshalls would be 

 expected to have few, if any, of Springer's (1982) Type 2 

 or 3 endemics. However, some care must be taken in 

 interpreting barnacle endemicity and distributional ranges. 

 Several of the taxa are so poorly known that distributional 

 records often indicate where a certain amount of work has 

 been done, not where the natural limits to distribution 

 occur. 



Many of the species reported from the Caroline Islands 

 could occur at Enewetak Atoll. Most have reasonably wide 

 western Pacific distributional ranges, and the proximity of 



