NUMBER 40 . 11 



approximately 4,000 specimens of coralline algae, including 

 C. compactiim, now housed at the Smithsonian's National 

 Museum of Natural History in Washington, DC. These collec- 

 tions have not been formally accessioned to the U.S. National 

 Herbarium, but are available by contacting the Hrst author. 

 During the 2010-2011 cruises, the bottoms from which the 

 collections were taken were extensively documented with 

 digital still images and video. This digital image archive will 

 be available with the collections. A single large sample of 

 several fused plants, partially reported here, was collected by 

 M. Goobie and E. Edinger at Arctic Bay in northern Baffin 

 Island at 72°N. Digital images of the cor-strome bottom in 

 Arctic Bay are available with the collection. 



Clathromorphum nereostratum (Aleutian Isu^nds) 



Three important C. nereostratum specimens utilized m this 

 study were collected by Lebednik (1976) at Amchitka; two oth- 

 ers were collected by R. Steneck in 2004. The remainder of the 

 material (21 specimens) was collected in the summer of 2008 by 

 ^ochen Halfar (JH, with S. Hetzinger and R. Steneck) on a cruise 

 from Akun Island ( 165°W) in the east to Attn Island (175°E) in 

 the western Aleutian chain. 



Specimen Preparation 



Many of the specimens collected from 1960 to 1964 were 

 diamond sawed into smaller blocks and then fixed, decalcified, 

 and microtome sectioned in paraffin before being studied with a 

 compound light microscope. A large microscope slide collection 

 remains part of this material. Recently collected large specimens 

 were usually first cut with a diamond saw and then fractured (es- 

 sentially randomly) with wire cutters. Fragments with the desired 

 orientation were then selected for mounting and then carbon 

 coated for examination with a Leica Stereoscan 440 scanning 

 electron microscope (SEM). 



Hiatella arctica is an abundant mollusk clathrostrome borer, 

 especially in the Labrador Sea but also in the Aleutian Islands 

 (Chenelot et al., 201 1). Shells of this bivalve are relatively soft and 

 ill suited to scraping; burrows are clearly constantly enlarged by 

 dissolution of the Clathromorphum skeleton, perhaps by release 

 of an acid. The net effect this enlargement is a natural etching of 

 the coralline skeleton. Burrow walls were extracted by diamond 

 sawing followed by wire cutter trimming. The appropriate sur- 

 faces, carbon coated for SEM examination, have been invaluable 

 for understanding biological and mineralogical patterns. 



The SEM images were typically taken at 50x, 500x, and 

 3,000x (occasionally at 10,000x) as appropriate to the data 

 sought. Although many single images were utilized, especially 

 of cellular and calcification features, often multiple images were 

 compiled into mosaics of vertical fractures. These mosaics allow 

 large-scale examination of conceptacle and anatomical layer- 

 ing as well as the determination of the vertical growth pattern 

 over time. Conceptacle-based growth rates were determined by 



aligning a fixed grid to the specimen growth lines on the mo- 

 saic then measuring yearly thickness wherever conceptacles were 

 present. These rates are supported by seasonal cycling of Mg as 

 measured by laser-mass spectrograph and electron microprobe. 

 Some direct measurements of yearly growth were made on so- 

 lution ridges in Hiatella cavities. Conceptacle dimensions were 

 obtained by measuring all conceptacles in a mosaic for which 

 the pore plate could be clearly discerned. Seasonal stages of re- 

 production were estimated by examining multiple, haphazardlv 

 selected specimens with a dissecting microscope. 



Terminology 



In this volume we use modified classical terms for coral- 

 line anatomy. Hypothallium applies to the basal cell filaments, 

 where the long axis of the cell is parallel to the substratum (in 

 Clathromorphum, multiple layers of cells grow parallel to the 

 substratum). The bulk of the thallus, built with filaments whose 

 cells have their long axis perpendicular to the substratum, is 

 termed the perithallium. When the intercalary meristem was 

 first described (Adey, 1964), two new cell types, the meristem 

 itself and the photosynthetic epithallium (previously called cover 

 cells) distal to the meristem, were added to the lexicon. In Clath- 

 romorphum, the cells of both perithallial and hypothallial fila- 

 ments become linked horizontally by fusion tubes that serve to 

 transport metabolites. Epithallium, perithallium, and hypothal- 

 lium are primary tissues; additional secondary tissues are formed 

 in reproduction and wound healing as we shall describe in this 

 volume. 



RESULTS 



Reproduction 



Like most corallines, Clathromorphum species have a basic 

 red algal triphasic life cycle in which isomorphic 2n (diploid) 

 plants (asexual in much of the literature) bear either /? (hap- 

 loid through meiosis) or 2n spores in sporangia, which are in 

 turn borne in reproductive structures called conceptacles. The 

 In spores produce new (asexual) spore-bearing plants. The n 

 spores, on the other hand, produce separate isomorphic male 

 and female plants. Both male and female plants produce either 

 spermatangia or carpogonia (egg cells) in similar conceptacles 

 that are typically considerably smaller than the asexual concep- 

 tacles. When the carpogonia are fertilized by the amoeboid sper- 

 matia released from the spermatangia, they produce fusion cells 

 that in turn develop filaments bearing 2n carpospores. This set of 

 In filaments, borne on the n female plants, is sometimes referred 

 to as a carposporophyte generation. The carpospores give rise 

 to the In (asexual) generation (Adey, 1965; Lebednik, 1976). 

 The maturing sporangia and/or their spores of both asexual 

 and carposporophyte concptacles dissolve the calcified perithal- 

 lium surrounding the conceptacle, considerably enlarging the 



