GAMMARIDEAN AMPHIPODA 13 



The occurrence of a coralline flora in the Phyllospadix-pelv etiid 

 zone of southern California not only seems to be associated with a 

 replacement of species of those subdominant amphipodan genera 

 occurring in middle California, but also with the occurrence of several 

 southern species and genera (at least in terms of frequency rankings). 



The dominant Amphipoda inhabiting the Phyllospadix-pelvetiid 

 zone are summarized in table 26. Twenty species are considered to 

 be numerically dominant in this zone but only a few are dominant at 

 any one locality. Fifteen of the species occur throughout the region 

 and 5 occur either north or south of Pt. Conception only. All of the 

 dominant species, except the last two, are also the most abundant 

 species of the zone (considered as a whole). Eight other species 

 appended to the list are also very abundant in the zone but never 

 dominate at any locality. The remaining species of the total of 72 

 occurring in the Phyllospadix-pelv etiid zone are of medium or low 

 frequency. 



Washes of sessile invertebrates. — Sessile organisms with 

 numerous cavities often harbor large numbers of small nestling 

 and commensal organisms. Pearse (1932), at the Dry Tortugas, 

 collected one loggerhead sponge containing more than 17,000 indi- 

 viduals of invertebrates, largely crustaceans. Nothing of that order 

 of magnitude has been collected in this survey, although the writer 

 estimates that some sponges collected in this survey have yielded 

 approximately the same density of crustaceans (100 per liter of 

 sponge). Sponges and tunicates have proved to be excellent nestling 

 sites for amphipods, second only to algae and surf grass. Most of 

 the sponges collected, except for some loggerheads (Spheciospongia 

 sp.), have been poor in vacuities; probably most of the Amphipoda 

 have been nestling externally or occupying domiciliary tubes attached 

 to the surfaces. Generally this situation is true also of tunicates. 

 Amaroucium spp. (table 16) are hosts for Polycheria osborni (see 

 Skogsberg and Vansell, 1928) but sample 38-F-l of Amaroucium sp. 

 was rich in non-polycheria Amphipoda which presumably inhabited 

 its partially sand-encrusted epifauna. Thin layers of encrusting 

 sponges and tunicates have very few amphipodan inhabitants. 



Because sponges and tunicates often were collected together in 

 mass samples, more discriminating work is required to discover the 

 precise host for the following Amphipoda apparently restricted to 

 those substates: Anamixis linsleyi, Leucothoides pacifica, Fresnillo 

 fimbriatus, Ocosingo borlus, Lysianassa pariter, L. dissimilis, Netame- 

 lita cortada, both species of Leucothoe, and the very small and thus 

 rare (because of screen sizes) Colomastix pusilla. 



