Lead

This chapter focuses on air temperature —that is, the temperature of the air as observed at 1.2 m (4 ft) above the ground surface. Air temperature conditions many aspects of human life, from the clothing we wear to the fuel costs we pay. Air tem-perature and air tempera-ture cycles also …

Feeding habits of gastropods are as varied as their shapes and habitats, but all include use of some adaptation of the radula. Most gastropods are herbivorous, rasping particles of algae from hard surfaces. Some herbivores are grazers, some are browsers, and some are planktonic feeders. Haliotis, the abalone, holds seaweed …

Torsion Gastropod development varies with the particular group under discussion, but in general there is a trochophore larval stage followed by a veliger larval stage where the shell first forms. The veliger has two ciliated velar lobes, used in swimming, and the developing foot is visible. The mouth is anterior …

Rotifers are dioecious, and males are usually smaller than females. However, despite having separate sexes, males are entirely unknown in the class Bdelloidea, and in the Monogononta they seem to occur only for a few weeks of the year. The female reproductive system in the Bdelloidea and Monogononta consists of …

Chitons (Gr. coat of mail, tunic)  repreent a somewhat more diverse molluscan group with about 1000 currently described species. They are rather flattened dorsoventrally and have a convex dorsal surface that bears seven or eight articulating limy plates, or valves, hence their name Polyplaophora (“many plate bearers”). The plates overlap …

For more than 50 years five classes of living molluscs were recognized: Amphineura, Gastropoda, Scaphopoda, Bivalvia (also called Pelecypoda), and Cephalopoda. Discovery of Neopilina in the 1950s added another class (Monoplacophora), and Hyman contended that solenogasters and chitons were separate classes (Aplacophora and Polyplacophora), lapsing the name Amphineura. Subsequently, Aplacophora …

অর্থনৈতিক দৈন্য মধ্যবিত্ত জীবনস্তরে জন্য এক মারাত্মক অভিশাপ। প্রাত্যহিক জীবনের ক্ষুদ্র ক্ষুদ্র স্বপ্ন আশা গুলো যখন দারিদ্র্যের কারণে প্রতিমুহূর্তে দলিত পিষ্ট ও চূর্ণবিচূর্ণ হতে থাকে,তখন তার স্বাভাবিক প্রতিক্রিয়ায় মধ্যবিত্ত হৃদয় হয়ে ওঠে আত্মকেন্দ্রিক, অপ্রতিভ, সংকুচিত ও আশাহীন বেদনায় পান্ডুর। দরিদ্র মধ্যবিত্তজীবনে বাস্তবতা ও স্বপ্নের যে দ্বন্দ্ব এবং অনিবার্যভাবে সেই দ্বন্দ্বের …

Mollusca (mol-lus’ ka) (L. molluscus, soft) is one of the largest animal phyla after Arthropoda. There are over 90,000 living species and some 70,000 fossil species. Molluscs are coelomate lophotrochozoan protostomes, and as such they develop via spiral mosaic cleavage and make a coelom by schizocoely. The ancestral larval stage …

Brachiopoda (brak-i-op’ – o-da) (Gr. brachio¯n, arm, pous, podos, foot), or lamp shells, are an ancient group. Although about 325 species are now living, some 12,000 fossil species, which once flourished in Paleozoic and Mesozoic seas, have been described. Modern forms have changed little from early ones. Genus Lingula (L. …

The enormous variety, great beauty, and easy availability of shells of molluscs have made shell collecting a popular pastime. However, many amateur shell collectors, even though able to nameh undreds of the shells that grace our beaches, know very little about the living animals that created those shells and once …