Question

3 turn the horseshoe crab over and observe the ventral surfaces of the cephalothorax and abdomen. notice that cephalothorax contains several pairs of modified appendages, including chelicerae, pedipalps, and walking legs. the small, inward - folding chelicerae are used to hold and chew food. the abdomen also has numerous pairs of highly modified appendages - platelike structures called gill opercula that conceal the delicate book gills underneath. beating of the gill opercula aids in swimming and aerates the book gills. 14 check your progress 1.1 how many compound eyes do horseshoe crabs possess? how many simple eyes? 1.2 what do you suppose is the purpose or function of the telson? 1.3 how many pairs of chelicerae do horseshoe crabs possess? how many pairs of pedipalps? how many pairs of walking legs? 1.4 how many opercula and book gills are present on your specimen? exercise 14 - 3 spiders, scorpions, ticks, and mites (subphylum chelicerata, class arachnida) arachnids are another class of arthropods in the subphylum chelicerata. unlike the class merostomata, however, which has only four extant species, the class arachnida is an incredibly large group with more than 110,000 named species. arachnids display tremendous diversity in appearance. like all chelicerates, arachnids lack antennae and the cephalothorax bears a single pair of chelicerae, a single pair of pedipalps, and four pairs of walking legs. yet, they exhibit enormous anatomic variation around these standard features. spiders, tarantulas, daddy longlegs, ticks, mites, chiggers, and scorpions all conform to this class of arthropods (fig. 14.6). arachnids are some of the oldest living arthropods and were among the first arthropods to inhabit land. fossilized scorpions nearly identical to those alive today have been found in rock dating back to the silurian period, 425 million years ago. most arachnids are carnivorous (with the exception of mites) and feed only on liquefied food, which they often obtain externally by injecting powerful enzymes into their prey with their fangs (modified chelicerae). they have been portrayed inaccurately as sinister animals with a deadly reputation - generating unreasonable fear among humans for centuries. in reality, most arachnids are timid creatures, biting only in defense, and then usually only after provocation. nearly all arachnids are terrestrial and have specialized respiratory structures called book lungs for breathing. small slits along the ventral surface of the abdomen allow air to enter a hollow compartment filled with numerous thin folds of the body wall that resemble pages of a book (hence the name). one side of each “page” is exposed to the air, and the inner layer of the page is bathed in hemolymph (blood), allowing gas exchange across the thin, moist surface.

Explanation:

1.1 Horseshoe crabs have 2 compound eyes and 5 - 7 simple eyes. The compound eyes are used for general vision and the simple eyes are light - sensitive and may help with orientation and detecting light changes.
1.2 The telson is used for steering and righting the horseshoe crab if it is flipped over. It is a long, spike - like structure at the rear of the body.
1.3 Horseshoe crabs have 1 pair of chelicerae, 1 pair of pedipalps, and 4 pairs of walking legs. The chelicerae are used for handling food, the pedipalps assist in feeding and locomotion, and the walking legs are for movement.
1.4 The number of opercula and book gills can vary among specimens, but typically there are multiple gill opercula (plates covering the book gills) and multiple book gills underneath for gas exchange.

Answer:

1.1 2 compound eyes, 5 - 7 simple eyes
1.2 Used for steering and righting
1.3 1 pair of chelicerae, 1 pair of pedipalps, 4 pairs of walking legs
1.4 Vary among specimens, multiple gill opercula and book gills for gas exchange