SOME LESSER KNOWN FEATURES OF THE ANCIENT CEPHALOPOD ORDER ELLESMEROCERIDA (NAUTILOIDEA, CEPHALOPODA)

Abstract:  Three specimens of the small breviconic ellesmeroceratid Paradakeoceras minor Flower, 1964 from the Tremadocian of the New York area preserve the annular elevation and muscle scars in moulds of the body chamber. The annular elevation is positioned at the base of the body chamber and is wider on the convex side of the shell than on the concave side. Multiple paired muscle scars can be seen within this annular elevation. A well-preserved body chamber of the breviconic ellesmeroceratid Levisoceras cf. edwardsi Ulrich, Foerste and Miller is described. Its body chamber shows a strong anterior–posterior asymmetry, which is common within the Ellesmeroceratida. The shape of the body chamber and of the soft body attachment structures has led to a reconstruction of an ellesmeroceratid soft body that is organized like a primitive conchiferan mollusc. Based on this reconstruction, a tryblidian cephalopod ancestor is supported. An evolutionary scenario is reconstructed from an ancestral nautiloid that is stretched along the anterior–posterior axis, and has serially arranged shell muscles and a small mantle cavity, towards a modern cephalopod with a dorsal–ventral body orientation, reduced number of shell muscles and a large mantle cavity.     

Underwater photogrammetry for close‐range 3D imaging of dry‐sensitive objects: The case study of cephalopod beaks

• Technical advances in 3D imaging have contributed to quantifying and understanding biological variability and complexity. However, small, dry‐sensitive objects are not easy to reconstruct using common and easily available techniques such as photogrammetry, surface scanning, or micro‐CT scanning. Here, we use cephalopod beaks as an example as their size, thickness, transparency, and dry‐sensitive nature make them particularly challenging. We developed a new, underwater, photogrammetry protocol in order to add these types of biological structures to the panel of photogrammetric possibilities.
• We used a camera with a macrophotography mode in a waterproof housing fixed in a tank with clear water. The beak was painted and fixed on a colored rotating support. Three angles of view, two acquisitions, and around 300 pictures per specimen were taken in order to reconstruct a full 3D model. These models were compared with others obtained with micro‐CT scanning to verify their accuracy.
• The models can be obtained quickly and cheaply compared with micro‐CT scanning and have sufficient precision for quantitative interspecific morphological analyses. Our work shows that underwater photogrammetry is a fast, noninvasive, efficient, and accurate way to reconstruct 3D models of dry‐sensitive objects while conserving their shape. While the reconstruction of the shape is accurate, some internal parts cannot be reconstructed with photogrammetry as they are not visible. In contrast, these structures are visible using reconstructions based on micro‐CT scanning. The mean difference between both methods is very small (10⁻⁵ to 10⁻⁴ mm) and is significantly lower than differences between meshes of different individuals.
• This photogrammetry protocol is portable, easy‐to‐use, fast, and reproducible. Micro‐CT scanning, in contrast, is time‐consuming, expensive, and nonportable. This protocol can be applied to reconstruct the 3D shape of many other dry‐sensitive objects such as shells of shellfish, cartilage, plants, and other chitinous materials.

     

Chromatophore radial muscle fibers anchor in flexible squid skin

Cephalopod skin is soft, flexible, and produces rapid color changes for camouflage and signaling primarily by regulating the shapes of its numerous chromatophore organs. Each chromatophore has 10–30 radial muscle cells, termed fibers, under central nervous system control. Each fiber contains myofilaments that contract in concert to stretch the pigment‐containing cell from its punctate, spherical state to a fully expanded thin disk of color. Expansion occurs in less than one second and can result in a 14‐fold expansion in pigment cell diameter. We investigated the anchoring mechanism of radial muscle fibers that expand pigment cells in the longfin squid, Doryteuthis (Loligo) pealeii. The proximal Active Zone of a radial muscle fiber adheres to the pigment cell within an ensheathing sinus. The distal portion forms terminal arbors, thereby increasing the surface area, to adhere it to the dermal extracellular matrix (ECM). While the muscle fiber is attached to the pigment cell with haptosomes, the remainder of the fiber is adhered to the surrounding basal lamina (part of the ECM) by numerous, closely spaced, small costamere‐like projections. Branching of the radial muscle fiber termini and the costamere‐like attachments are key anatomical specializations that anchor the radial muscle fibers in the pliable skin while allowing the freedom of movement required for large changes in pigment cell diameter. We postulate that these features may be relevant for the development of soft actuation models in materials science.     

Cuttlefish camouflage: a quantitative study of patterning

To investigate camouflage design, we compared the responses of two species of cuttlefish ( Sepia officinalis and Sepia pharaonis ) with controlled but naturalistic backgrounds, consisting of mixtures of 1-mm and 9-mm diameter coloured pebbles. Quantitative analysis of image data using methods adapted from functional imaging research found differences in how the two species camouflage themselves. Whereas S. officinalis switches from background resemblance to a disruptive pattern as it moves from a fine to a coarsely patterned background particle, S. pharaonis blends the two types of pattern. We suggest that the differences may arise because S. pharaonis needs to produce camouflage that is effective when viewed over a relatively wide range of distances.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 335–345.     

Cuttlefish use visual cues to determine arm postures for camouflage

To achieve effective visual camouflage, prey organisms must combine cryptic coloration with the appropriate posture and behaviour to render them difficult to be detected or recognized. Body patterning has been studied in various taxa, yet body postures and their implementation on different backgrounds have seldom been studied experimentally. Here, we provide the first experimental evidence that cuttlefish (Sepia officinalis), masters of rapid adaptive camouflage, use visual cues from adjacent visual stimuli to control arm postures. Cuttlefish were presented with a square wave stimulus (period = 0.47 cm; black and white stripes) that was angled 0°, 45° or 90° relative to the animals' horizontal body axis. Cuttlefish positioned their arms parallel, obliquely or transversely to their body axis according to the orientation of the stripes. These experimental results corroborate our field observations of cuttlefish camouflage behaviour in which flexible, precise arm posture is often tailored to match nearby objects. By relating the cuttlefishes' visual perception of backgrounds to their versatile postural behaviour, our results highlight yet another of the many flexible and adaptive anti-predator tactics adopted by cephalopods.     

Stomach contents of mass-stranded short-finned pilot whales (Globicephala macrorhynchus) from North Carolina

We examined the stomach contents of 27 short‐finned pilot whales (Globicephala macrorhynchus) that mass stranded on the North Carolina coast on 15 January 2005. Eleven whales had prey parts in their forestomachs. We used frequency of occurrence and numerical abundance to assess the relative importance of prey. Brachioteuthis riisei (numerical abundance 28%), an oceanic species, was the most important cephalopod prey, but Taonius pavo (12%) and Histioteuthis reversa (9%) also represented a substantial part of the diet. A large number of otoliths belonging to the fish Scopelogadus beanii were present (25%). These results differ from reports of the stomach contents of short‐finned pilot whales from the Pacific coast in which neritic species dominate the diet. Our findings also suggest that there is a considerable difference between the diet of short‐ and long‐finned pilot whales (Globicephala melas) in the western North Atlantic. The latter feed predominantly on the long‐finned squid (Loligo pealei) whereas the former feed on deep‐water species. Our results indicate the whales fed primarily off the continental shelf prior to stranding.     

Organization of the nervous system in the pygmy cuttlefish,Idiosepius paradoxus ortmann (Idiosepiidae,Cephalopoda)

The idiosepiid cuttlefish is a suitable organism for behavioral, genetic, and developmental studies. As morphological bases for these studies, organization of the nervous system was examined in Idiosepius paradoxus Ortmann, 1881, using Cajal's silver technique and immunohistochemical staining with anti-acetylated alpha-tubulin antibody. The nervous architecture is generally identical to that described in Sepia and Loligo, but some features characterize the idiosepiid nervous system. The olfactory system is highly developed in the optic tract region. The dorsolateral lobes show large neuropils, connected with each other by a novel well-fasciculated commissure. Each olfactory lobe is subdivided into two lobules. The neuropils of the anterior and the posterior chromatophore lobes are very poorly developed. Neuronal gigantism is not extensive in the brain; enlarged neuronal cells are visible only in the perikaryal layer of the posterior subesophageal mass. The giant nerve fiber system is of the Sepia type; the axons are not markedly thick and the first-order giant fibers do not fuse with each other at the chiasma. Three-dimensional images by whole-mount immunostaining clarified the innervation pattern in the peripheral nervous system in detail. Two commissural fibers link the left and right posterior funnel nerves ventrally and dorsally. The stellate commissure, which is absent in Sepia and Sepiola, connects the stellate ganglia with each other. A branch of the visceral nerve innervating the median pallial adductor muscle is characteristically thick. Tubulinergic reactivity of the cilia and axons reveals the presence of many ciliated cells giving off an axon toward brain nerves in the surface of the funnel, head integument, arm tips, and epidermal lines. Some of these features seem to reflect the inactive nekto-benthic life of the idiosepiid cuttlefish in the eelgrass bed.     

The genetic structure of Nautilus pompilius populations surrounding Australia and the Philippines

Understanding the distribution of genetic diversity in exploited species is fundamental to successful conservation. Genetic structure and the degree of gene flow among populations must be assessed to design appropriate strategies to prevent the loss of distinct populations. The cephalopod Nautilus pompilius is fished unsustainably in the Philippines for the ornamental shell trade and has limited legislative protection, despite the species' recent dramatic decline in the region. Here, we use 14 microsatellite markers to evaluate the population structure of N. pompilius around Australia and the Philippines. Despite their relative geographical proximity, Great Barrier Reef individuals are genetically isolated from Osprey Reef and Shark Reef in the Coral Sea (F_ST = 0.312, 0.229, respectively). Conversely, despite the larger geographical distances between the Philippines and west Australian reefs, samples display a small degree of genetic structure (F_ST = 0.015). Demographic scenarios modelled using approximate Bayesian computation analysis indicate that this limited divergence is not due to contemporary gene flow between the Philippines and west Australia. Instead, present‐day genetic similarity can be explained by very limited genetic drift that has occurred due to large average effective population sizes that persisted at both locations following their separation. The lack of connectivity among populations suggests that immigrants from west Australia would not facilitate natural recolonization if Philippine populations were fished to extinction. These data help to rectify the paucity of information on the species' biology currently inhibiting their conservation classification. Understanding population structure can allow us to facilitate sustainable harvesting, thereby preserving the diversity of genetically distinct stocks.