File:American malacological bulletin (1988) (18129883066).jpg

Title: American malacological bulletin
Identifier: americanmal6719881990amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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142 AMER. MALAC. BULL. 6(1) (1988)
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Fig. 1. Diagram of five types of spicules and one spine, a. Primary spicule from a newly metamorphosed juvenile. Note thin chitinous cup. b. Spicule with apically and basally thick cup. c. Spicule with pigment granules and shaft, d. Spicule with an annulate shaft sur- mounting a sensory nodule, e. Spicule as in d but with an articulated shaft (from Leise, 1983). As will be described below, most hairs contain or are in contact with dendrites from presumptive sensory neurons. This paper reviews the morphology of chiton hairs while focus- ing on their neuronal elements and describes the relation- ships of these hairs to other girdle ornaments. DIVERSE GIRDLE HAIRS: AN OVERVIEW Hairs occur in a bewildering range of sizes and con- figurations in species from at least five families: Chitonidae; Lepidochitonidae (Ferreira, 1982); Callochitonidae; Chaeto- pleuridae; and Mopaliidae (classification after Bergenhayn (1955) unless otherwise cited). In addition, hairs from many species of chitons will erode during the animal's lifetime. Thus, it can be difficult to understand the morphology of a particular type of hair if only large hairs or hairs from old animals are studied. Species such as Chiton olivaceus Spengler, 1797 (fam- ily Chitonidae) can produce small marginal hairs 80 to 100 ^m long (Plate, 1902). In the Lepidochitonidae (Ferreira, 1982), species such as Tonicella insignis Reeve, 1847 produce small, simple hairs only 100 jum long (Leise, 1983), while others, such as Dendrochiton lirulatus Berry, 1963, produce tufts of hairs up to 500 nm long. Hairs from species of Callochitonidae, such as Eudoxochiton nobilis Gray, 1843, often have large ar- ticulated shafts about 1.5 mm in length (Leise, 1983). On in- tact animals of E. nobilis, even the distal spicules can be discerned. Species in the Chaetopleuridae and Mopaliidae also display hairs in a wide range of sizes; although the Chaetopleuridae characteristically produce hairs (Pilsbry, 1893), some species, like Chaetopleura lurida (Sowerby, 1832) secrete none. The girdle of this species bears spicules with articulated and simple shafts. A congener, C. peruviani Lamarck, produces similar spicules whose elongated shafts extend beyond the cuticular surface and so earn them the designation of hair (Plate, 1902; Fischer-Piette and Franc, 1960) (Fig. 4). Among the Mopaliidae are also species that produce small, simple hairs, such as those on Katharina tunicata Wood, 1815 or very large, simple hairs, as are found on Plaxiphora obtecta (Carpenter in Pilsbry, 1893) (Table 1). Most of the above mentioned hairs conform to the hypothesis of Thiele (1929) and Hyman (1967) that hairs are elongated spicule shafts. However, the large hairs secreted by species in the genera Mopalia and Placiphorella, and those secreted by some of the Lepidochitonidae, namely Lepido- chitona flectens (Carpenter, 1864), and species in the genus Dendrochiton Berry, 1911 (Ferreira, 1982), do not conform to Thiele's (1929) and Hyman's (1967) hypothesis. These latter types of hairs are composite structures, built by the replica- tion of many basic units. They are not simply enlarged or elongated spicule shafts. In the genus Mopalia, the basic unit construct is a calcareous spicule and its long chitinous shaft. This basic unit is serially repeated along an outgrowth of the cuticle, and with the exception of the groove along which these spicules lie, the entire organ is surrounded by one or two distinct layers of dense cortical material (Fig. 5) (Leloup, 1942; Table 1. Characteristics of chitons hairs in the family Mopaliidae (Structure: C = compound; S = sim- ple and lacking medulla. Length and width are maxima recorded. Cortex: ++ = >20 nm thick; + = <20 ^m thick; - = lacking). Species Hair Length Hair Width Structure Cortex Innervation (mm) (/tm) Mopalia muscosa 5 M. ciliata 3 M. lignosa 3 M. hindsii 2.5 Plaxiphora obtecta 2 Katharina tunicata 0.1 Placiphorella velata 5 400 C ++ + 200 C ++ + 300 C + + 80 C + + 300 S ++ - 5 S + + 400 C - +

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