American malacological bulletin (1988) (17533862354)

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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ROLLER AND STICKLE: THAIS INTRACAPSULAR DEVELOPMENT 191 Total organic material was calculated by subtracting the total ash (inorganic) from the pre-combustion dry weight. Day 1 and Day 10 calcium, organic, and other inorganic levels were compared by a two-sample t-test (Steel and Torrie, 1980). RESULTS COPULATION AND CAPSULE DEPOSITION Copulation in the drills was observed in the field from late April to late June, 1982 and from late April to early June, 1983. During these months snails were found in large breeding aggregations which extended from approximately 0.5 m above the water surface at low tide to 1 m in depths. The number of snails comprising each aggregation varied from 6 to 27 in- dividuals. Drills collected in early June, 1983 began copulating in the laboratory within 5 days. The duration of copulation was variable, lasting from approximately 2.5 hours to 3 days. Dur- ing copulation the male crawled onto the shell of its partner and inserted its penis into the right side of the mantle cavity. Spermatozoa and prostatic secretions were presumably dis- charged into the genital aperture of the female (Fretter and Graham, 1962). Egg capsule deposition occurred as early as six hours and up to sixty days after copulation was observed. In the laboratory, the egg capsules were attached to the glass walls of the aquaria, usually near the exhalant port of the undergravel filter system. Rarely were capsules deposited on oyster shells; however, oysters covered with Thais egg cap- sules have been collected from Grand Isle. Capsule deposi- tion was intermittent. Snails were observed to cease deposi- tion for a while, feed on oysters, and then resume deposition, sometimes in an entirely different location. Snails tended to attach their capsules together forming one large communal mass. The intermittent feeding behavior as described above and the communal egg masses made distinguishing which female laid specific capsules difficult. The number of capsules obtained from any one snail varied; however, most drills deposited 20-30 capsules in a mass. The duration of capsule deposition also varied, from as short as 2-3 hours to as long as 6-7 days. Snails were also observed to pause during deposition and remain on the capsule mass without feeding for several hours before resuming capsule laying. Capsules were usually attached by their bases (Fig. 1), and formed a single layer on the substratum. In several cases capsules were observed attached together at various locations along their lengths; however, attachment never obstructed the opercular opening of any capsule in a mass. Butler (1954) reported similar findings. The egg capsules of Thais haemastoma canaliculata are similar to those of T. haemastoma floridana as described by DAsaro (1966). The capsules are somewhat conical in ap- pearance, possessing a broad flat apical plate and tapering down to the base where they are typically attached to the substratum (Fig. 1). Each capsule possesses a convex and concave side along most of its length, giving the capsule an oblong appearance in cross section at the distal end (Fig. 2). However, the capsule is more circular in cross-section at its

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Fig. 1. Light micrograph of typical Thais haemastoma egg cases con- taining embryos. Hatching occurred approximately three days later (O, operculum). Fig. 2. Scanning electron micrograph (SEM) of an opercular view of an egg capsule (Cc, concave wall; Cv, convex wall; O, opercular plug; P, one lateral protuberance). Fig. 3. SEM of cap- sule cross-section showing both inner and outer walls (Iw, inner cap- sule wall; Ow, outer capsule wall; P, lateral protuberance). Fig. 4. SEM of capsule protuberance outlined in (3) (D, lateral dense layers of outer capsule wall; Iw, inner capsule wall; S, medial spongy mass of outer capsule wall). tapered base. Four longitudinal ridges (2 on each side) separate the convex and concave sides. The two ridges on each side merge at the apical plate forming a lateral pro- tuberance (Figs. 2-4). Each capsule is composed of a thick fibrous-appearing outer wall and a thin membranous inner wall, which readily separate during microscopical preparation (Fig. 3). The entire outer capsule wall appears to be composed of two compact, dense lateral layers and a spongy-fibrous medial layer (Fig. 4). The protuberances and ridges repre- sent sculpturing of the outer wall only and do not make up any portion of the inner wall, which encloses the embryos and the nutritive albumen. A round, discoidal opercular plug is located on the apical plate at the distal end of each capsule (Fig. 2). The operculum swells and bulges outward a few days prior to hatching. At hatching the operculum disintegrates leaving a prominent opercular scar. Capsule length varied from 0.84-1.13 cm (x ± S.E.= 0.95 ± 0.01 cm; N=40). Capsule wall and capsule content dry weight varied from 0.47-1.57 mg (x ± S.E.= 1.05 ± 0.05 mg; N = 40) and from 0.14-1.20 mg (x ± S.E.= 0.54 ± 0.04

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1988

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