Abstract
Sea pigs (Scotoplanes spp.) are deep-sea dwelling sea cucumbers of the phylum Echinodermata, class Holothuroidea, and order Elasipodida. Few reports are available on the microscopic anatomy of these deep-sea animals. This study describes the histologic findings of two, wild, male and female Scotoplanes sp. collected from Monterey Bay, California. Microscopic findings were similar to other holothuroids, with a few notable exceptions. Sea pigs were bilaterally symmetrical with six pairs of greatly enlarged tube feet arising from the lateral body wall and oriented ventrally for walking. Neither a rete mirabile nor respiratory tree was identified, and the large tube feet may function in respiration. Dorsal papillae protrude from the bivium and are histologically similar to tube feet with a large, muscular water vascular canal in the center. There were 10 buccal tentacles, the epidermis of which was highly folded. Only a single gonad was present in each animal; both male and female had histologic evidence of active gametogenesis. In the male, a presumed protozoal cyst was identified in the aboral intestinal mucosa, and was histologically similar to previous reports of coccidians. This work provides control histology for future investigations of sea pigs and related animals using bright field microscopy.
Highlights
Sea pigs (Scotoplanes spp.) are animals of the phylum Echinodermata, class Holothuroidea, and order Elasipodida
All echinoderms have a unique type of connective tissue called mutable collagenous tissue that allows them to relax and stiffen their dermis at will
Mutable collagenous tissue is necessary for evisceration and autotomy, which allows echinoderms to voluntarily expel internal viscera and release arms, respectively
Summary
Sea pigs (Scotoplanes spp.) are animals of the phylum Echinodermata, class Holothuroidea, and order Elasipodida. The order Elasipodida includes holothuroids that are deep-sea dwelling [3]. The dorsal papillae ( known as antennae; [20]), eviscerated digestive tract, gonads, and buccal tentacles were cut away from the body; additional transverse and longitudinal sections were made of these organs and processed for histology.
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