An ultrastructural study of connective tissue in mollusc integument III

Abstract

We studied structure and ultrastructure of the subepidermal connective tissue (SEC) of the integument of three cephalopods (Sepia officinalis, Octopus vulgaris and Loligo pealii). In all species, three distinct regions of the SEC were recognised: (a) an outer zone (OZ) that included the dermal-epidermal junction, and consisted of a thin layer of connective tissue containing muscles, (b) an extensive middle zone (MZ) containing a compact network of collagen fibres and numerous cells, (c) an inner zone (IZ) of loose connective tissue that merged with muscular fascia. This arrangement differs from that in bivalves and gastropods and recalls vertebrate integument. The dermal-epidermal junction of cephalopods differed from that of bivalves, gastropods and mammals in that the epidermal cells did not possess hemidesmosomes, and their intermediate filaments terminated directly in the plasmamembrane. The thick (120-500 nm) basal membrane (BM) had a superficial zone containing a regular array of granules; a lamina densa composed of a compact network of small filaments and granules; and an IZ distinguished by expansions of granular material protruding into underlying structures. Collagen fibres contained fibroblast-derived cytoplasmic thread, running through their centres and were surrounded by granular material that joins them to adjacent fibres. The collagen fibrils were of medium diameter (30-80 nm) had the typical ultrastructure of fibrillar collagens, and were surrounded by abundant interfibrillar material. The hypodermis was loose, with a network of small bundles of collagen fibrils. Cephalopod integument appears to represent a major evolutionary step distinguishing this class of molluscs.

Collagen fibrils of an invertebrate (Sepia officinalis) are heterotypic: immunocytochemical demonstration

“…We chose Sepia dermis for investigation since it is rich in collagen fibrils (Bairati et al, 2003) that are easily isolated. Furthermore, Sepia belongs to a highly evolved and differentiated invertebrate class (Cephalopoda), and several types of collagen (type I-like, type IV, type V, and type VI) have previously been identified in this animal.…”

Characterization of the adhesive areas in Sepia tuberculata (Mollusca, Cephalopoda)

“…There are only a few descriptions of the mantle in cephalopods; the few muscle layers described for the dermis of Octopus and Sepia are in close association with the basal lamina or the mantle musculature (Brocco,1976; Bairati et al,2003). Additional to this association, the dermal muscle layers in S. tuberculata are thicker, uniformly distributed, and are strongly interconnected.…”

An ultrastructural study of cell junctions and the cytoskeleton in epithelial cells of the molluscan integument

“…These junctions are vital elements of the dermo-epidermal junction whose detailed nature varies between the three molluscan classes studies (Bairati et al, 2000(Bairati et al, , 2001(Bairati et al, , 2003 and overall differs clearly from the dermoepidermal junction of mammals.…”

“…At first sight the mode in which cephalopod epidermis is attached to the underlying connective tissue would appear less complex than the hemidesmosome connections found in gastropods and bivalves. However, in cephalopod epidermis the upper part of the basement membrane is characterized by a particularly thick lamina densa from which numerous stubby extensions protrude towards the cell membrane so that a lamina lucida seems to be absent (Bairati et al, 2003). These protrusions probably interact with attachment proteins that in turn bind the intermediate filaments.…”