File:American malacological bulletin (1988) (18129812356).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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106 AMER. MALAC. BULL. 6(1) (1988)
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Figs. 115-117. Acanthochitona zebra Lyons, sp. nov. Fig. 115. Holotype, 15.0 mm; Freeport, Grand Bahama; USNM 859319. Fig. 116. Paratype, 8.3 mm; Tamarind Beach Reef, Grand Bahama; FSBC I 32482. Fig. 117. Paratype, 11.1 mm; Dry Tortugas, Florida; FSBC I 32478. DESCRIPTION: Largest specimen (holotype) 15.0 mm long, 7.2 mm wide including girdle; valves and girdle occupying ap- proximately equal portions of total specimen width (Figs. 115-117). Valve i with 3-5 olivaceous or brown concentric bands, expressed on valves ii-vii as transverse stripes (chevrons) extending posterolaterally from jugum; bands usually strongest on valves i-v, commonly obscured by overall dark olive or brown color on valves iv and vii; valve viii most- ly white, with single large olivaceous spots on lateral areas. Girdle white with irregular olivaceous or green bands cross- ing upper surface from valves to peripheral margins, sometimes with broad, black spots at middle or elsewhere on each side. Valve i semilunate (Fig. 118), wider than long, posterior margin straight, slightly beaked, with anterior insertion plate bearing 5 slits; tegmentum occupying 80-85% of valve length. Valves ii-vii strongly beaked posteriorly (Fig. 119); tegmentum evenly to broadly pentagonal, with convex anterolateral margins; sutural laminae moderately narrow, curving anteromedially from posterolateral corners of tegmentum, with subacute anterior tips separated by broad sinus of same width as anterior end of jugum; single narrow slits along lateral margins. Valve viii tegmentum roughly ovate, widest mesial- ly, truncate anteriorly, extending to overhang posterior edge of insertion plate (Fig. 120). Mucro distinctly posterior; sutural laminae extending obliquely anteriorly, subquadrate, of moderate length; two slits in posterior insertion plate very fine, barely discernible with dissecting microscope. Valve mor- phology of Puerto Rican juveniles and Floridan adults as il- lustrated (Figs. 121-126). Jugum of valves ii-viii smooth, wedge-shaped, widest anteriorly. Tegmentum covered with densely packed, flattened, spatulate pustules (Fig. 127), approximately 80-100 /jm long, 70 /im wide, radiating anteriorly from beak of valve i, anterolaterally from jugum of valves ii-vii, and from mucro of valve viii; pustules with single macresthete near apex, 4-7 micresthetes surrounding macresthetes, sometimes more on Florida specimens; many additional micresthetes dispersed across surface of tegmental plain. Girdle upper surface covered with fine (100 ^m) spicules; 18 anterior and sutural tufts comprised of 8-10 red- dish brown, amber, or white, moderately long (to 650 /xm), slightly curved, blunt-tipped spicules; marginal spicules straight or slightly curved, approximately 550 iim long, with blunt tips, white, sometimes alternating with amber; under- side covered with fine (60 ^m), sharp-tipped spicules directed toward periphery. DISCUSSION: The olivaceous stripes on the tegmentum of Acanthochitona zebra strongly resemble those of A. lineata, and A. astrigera sometimes has white stripes or maculations on the dark blue-green tegmentum of some valves. Moreover, all three species occurred together at the type-locality of A. zebra. However, A. zebra can be separated readily from the other two species by its extremely posterior mucro, from which the tegmentum drops rapidly to overhang the posterior inser- tion plate, and by the dorsal tufts of the girdle, which contain only 8-10 blunt-tipped spicules. Pustular shape, as well as location of macrestheses and micresthetes, further distinguish A. zebra from A. astrigera and A. lineata. Valve proportions of Florida specimens differ somewhat from those of specimens from the Bahamas and Puerto Rico, but morphology of valve viii and the tegmental pustules, as well as the color pattern, indicate they are conspecific. Five RMNH lots from Aruba and Curacao appear to be this species, but the concentric bands and stripes are only weakly ex- pressed on the four largest (5.2-7.3 mm) specimens and are not evident at all on the five smaller (2.7-3.4 mm) specimens.

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