ALBERT

Description: A series of experiments was carried out to investigate the nature and controls (oxygen, microbial populations, agitation) on the degradation of soft tissues. Decay was monitored in terms of morphological change, weight loss, and change in chemical composition in the polychaete Nereis virens. Polychaetes include a range of tissue types of differing chemical composition and preservation potential: muscle, cuticle, setae, and jaws. Regardless of conditions, all the muscle had broken down and fluid loss through the ruptured cuticle had reduced the carcass to two dimensions within 8 days at 20°C. In most cases some cuticle, in addition to the jaws and setae, remained after 30 days. Where oxygen was completely eliminated, the rate of decay of the more volatile issues was significantly reduced. The degree of both osmotic uptake of water by the carcass and changes in water pH differed depending on whether the system was open or closed to oxygen diffusion. Autolytic and chemical processes are not sufficient to fully degrade the carcass in the absence of bacteria. Where internal bacteria are present, the presence or absence of water column bacteria made little difference to decay rate. Initial degradation (in the first 3 days) affects mainly the lipid fraction and the collagen of the cuticle. Later decay reduces the nonsoluble protein and increases the relative proportion of refractory structural components (tanned chitin and collagen) to more than 95% by day 30. Thus, only the sclerotized tissues are likely to survive beyond 30 days in the absence of early diagenetic mineralization. The sequence of degradation predicted from the relative decay resistance of macromolecules in the sedimentary record (protein → carbohydrate → lipid) is not, therefore, a consistent indicator of the preservation potential of structural tissues which incorporate them.The experiments reveal five stages in the decay of polychaete carcasses; whole/shriveled, flaccid, unsupported gut, cuticle sac, jaws and setae. All are represented in the fossil record. This allows an estimation of how far decay proceeded before it was halted by the fossilization process. The most complete preservations occur in the Cambrian where the Burgess Shale preserves evidence of muscle tissues. Traces of the gut and cuticle are more widely preserved, as at Mazon Creek, Grès à Voltzia, Solnhofen, and Hakel. Preservation varies within Konservat-Lagerstätten. The most common whole body preservation includes only the more recalcitrant tissues, jaws (where present) and setae, with an impression of the body outline. The stage of decay can be used as a taphonomic threshold, to provide an indication of how significantly the diversity of an exceptionally preserved biota is likely to have been reduced by taphonomic loss.

Description: Some of the limits to the use of serology to identify prey species in the digestive tracts of cephalopods have been evaluated. Cuttlefish, Sepia officinalis, were given meals of krill slurry (Euphausia superba). Protein extracts of contents from four regions of the digestive tract, stomach, caecum, digestive gland and intestine, were tested for prey antigenicity. Digestion times (loss of antigenicity) ranged from 1 to 8 h depending on sampling site. Stomach and caecum emptied rapidly, but meal antigenicity persisted longer in the digestive gland. The Sepia experiments provide a basis for interpretation of results from natural predation by cephalopods).

Description: The alimentary tracts of 12 species of Antarctic squid were examined visually and serologically for the presence of Euphausia superba. Only four species, Alluroteuthis antarcticus, Galiteuthis glacialis, Martialia hyadesi and Psychroteuthis glacialis, contained material which was identifiable to species visually. Myctophid fish and euphausiids were the most common prey item. Serology showed that specimens of six species had eaten euphausiids. Where antisera showed cross-reactions with other potential prey species, biogeographical and haul data was used to determine the species of Euphausia consumed. P. glacialis (n=19) had consumed E. superba. Mastigoteuthis psychrophila (n=10) had eaten E. superba and/or E. triacantha. Brachioteuthis picta (n=6), M. hyadesi (n=27), and two Moroteuthis spp. (n=2) had consumed unidentified euphausiids. Bathyteuthis abyssicola (n=13) and Histioteuthis eltaninae (n=13) had not preyed on euphausiids. B. picta appeared to have fed in the net.

Description: The functional morphology of the buccal mass of 23 species of cephalopod (Octopoda, 4 species; Teuthoidea, 17; Sepioidea, 2) was investigated by gross dissection, histology and observations on fresh preparations. Cephalopod beaks lack a joint or articulation point. The jaws slide and rotate around an area rather than a fixed point. During closing the superior mandibular muscle (SMM) provides the force of a bite and the largest movement vector, whilst the inferior mandibular muscle (IMM) acts to retract the upper beak, causing shearing action. Dorsal portions of the lateral mandibular muscles (LMM) flex the upper beak walls outwards, probably to accomodate the backwards sweep of the radula and buccal palps during closing. To open the beaks, the ventral portions to the lateral mandibular muscles pull the rear lateral walls of the two beaks towards each other, moving the lower beak back relative to the upper. The buccal mass weighs more in decapods (0.65-4.34% of body weight) than octopods (0.49-0.77%). The weight difference is mainly accounted for by the size of the superior mandibular muscle. Beak shape and muscle volume are related. Increasing the size of the upper beak hood and lateral wall area results in larger SMM and LMM respectively Increasing hood size in the lower beak increases IMM size, and altering the angle by which the wings meet the lateral wall changes the volume of the SMM and LMM. To accomodate the decapod pointed upper rostrum, the lateral walls of the lower beak have shortened in length, whilst increasing in breadth and surface relief to maintain the area available for muscle insertion. In species with a lateral wall ridge or fold (e.g. Onychoteuthis) this may mark the insertion point of the LMM.