Tag Archives: class

Order Opiliones: Harvestmen Harvestmen, often known as “daddy longlegs,” are common throughout the world and comprise about 5000 species. They are easily distinguished from spiders: their abdomen and cephalothorax are rounded and broadly joined, without the constriction of a pedicel; their abdomen shows external segmentation; and they have only two …

Order Scorpiones: Scorpions Scorpions are perhaps the most ancient of terrestrial arthropods and comprise about 1400 species worldwide. Although scorpions are more common in tropical and subtropical regions, some occur in temperate zones. Scorpions are generally secretive, hiding in burrows or under objects by day and feeding at night. They …

Arachnids (Gr. arachne¯, spider) exhibit enormous anatomical variation. In addition to spiders, the group includes scorpions, pseudoscorpions, whip scorpions, ticks, mites, daddy longlegs (harvestmen), and others. There are many differences among these taxa with respect to form and appendages. They are mostly free-living and are most common in warm, dry …

Class Pycnogonida: Sea Spiders About 1000 species of sea spiders occupy marine habitats ranging from shallow, coastal waters to deep-ocean basins. Some sea spiders are only a few millimeters long, but others are much larger with legspans up to nearly 0.75 m. They have small, thin bodies and usually four …

Class Hirudinida is divided into three orders, Hirudinea, the “true” leeches, and two others that merit mention here because their members are morphological intermediates between oligochaetes and true leeches. Oligochaetes have variable numbers of segments, segments bear setae, and there are no suckers on the body. True leeches have 34 …

Class Oligochaeta More than 3000 species of oligochaetes are found in a great variety of sizes and habitats. They include the familiar earthworms and many species that live in freshwater. Most are terrestrial or freshwater forms, but some are parasitic, and a few live in marine or brackish water. With …

Bivalvia are also known as Pelecypoda (pel-e-sip o-da), or “hatchet-footed” animals, as their name implies (Gr. pelekys, hatchet, pous, podos, foot). They are bivalved molluscs that include mussels, clams, scallops, oysters, and shipworms and they range in size from tiny seed shells 1 to 2 mm in length to giant …

Cephalopoda (Gr. kephal¯e, head, + pous, podos, foot) include squids, octopuses, nautiluses, devilfish, and cuttlefish. All are marine, and all are active predators. Their modified foot is concentrated in the head region. It takes the form of a funnel for expelling water from the mantle cavity, and the anterior margin …

The largest class of annelids is the Polychaeta (Gr. polys, many, chaite¯, long hair) with more than 10,000 species, most of them marine. Although most polychaetes are 5 to 10 cm long, some are less than 1 mm, and others may be as long as 3 m. They may be …