. The biology of marine animals. Marine animals; Physiology, Comparative. DIGESTION 261 pteropods. Proteases and sucrases are secreted into the gut in other gastropods (vide infra) (46). Limulus and pycnogonids among arthropods retain a degree of in- tracellular digestion. The food of Limulus consists of polychaetes and lamellibranchs which are torn up by the gnathobases of the walking legs before being swallowed. Enzymes, including proteases, are released into the stomach cavity but the breakdown of proteins is completed intracel- lularly, within the cells of the digestive gland, by an intrac
. The biology of marine animals. Marine animals; Physiology, Comparative. DIGESTION 261 pteropods. Proteases and sucrases are secreted into the gut in other gastropods (vide infra) (46). Limulus and pycnogonids among arthropods retain a degree of in- tracellular digestion. The food of Limulus consists of polychaetes and lamellibranchs which are torn up by the gnathobases of the walking legs before being swallowed. Enzymes, including proteases, are released into the stomach cavity but the breakdown of proteins is completed intracel- lularly, within the cells of the digestive gland, by an intracellular dipepti- dase. The food of pycnogonids consists of fluids, soft tissues and fine par- ticles. Secretory cells in the midgut release extracellular enzymes, while absorptive cells in the same region ingest materials and complete digestion, especially of proteins, intracellularly. In addition to the gut epithelium proper, phagocytic amoebocytes also ingest and decompose food particles in certain animals. Intracellular Digestion by Amoebocytes. Intracellular digestion of food particles by wandering amoebocytes takes place in lamellibranchs Posterior Rectum adductor / Aorta. Ventricle Auricle. l,ver Ctenidium Intestine Caecum Fig. Internal Anatomy of the Shipworm Bankia gouldi. Anterior Half of the Body, with Left Valve, Mantle and Gill removed (after Sigerfoos, 1907.) and echinoderms. Amoebocytes are numerous about the stomach, digestive diverticula and midgut of bivalve molluscs, and it has been observed that these cells pass through the epithelium of the gut into the lumen, where they ingest food particles, and then return to the tissues to digest this material. Under abnormal conditions the amoebocytes may pass through the gill membranes and absorb food material from the mantle cavity. Digestive amoebocytes occur in the gut of filter-feeding lamellibranchs but are absent in protobranchs and carnivorous septibranchs. The digestive capacity of amoebocytes has been inv
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