External Structure of Porcellio scaber
The diagram below shows the dorsal (upper) view of Porcellio scaber. In woodlice the 1st segments of the thorax are fused with the head. The last upper (dorsal) segments overlap the segments of the abdomen. Often the terms head, pereion and pleon are used instead of head, thorax and abdomen as in other arthropods. There are two pairs of antennae, however the inner pair are very small and difficult to see. Porcellio scaber has 2 compound eyes.
The next diagram shows the ventral (lower) surface of a male Porcellio scaber. Females lack the genital projections and may have a yellowish brood pouch containing eggs or young at the posterior (rear) end of the abdomen. This diagram only shows the 1st two pairs of legs, there are 7 pairs of legs in total, one pair on each of the 7 thoracic segments. The "lungs" show up as whitish patches on the 1st pair of pleopods, they have a pore which allows gases to diffuse in and out of the pseudo-lung. The pore is not able to be closed as is the case with insects, this means that woodlice are more prone to desiccation than are insects.
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