From ZooTerms (Dictionary of Invertebrate Zoology)
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rostrum (noun; plural -tra; Latin rostrum, beak): 1. A beak or snout. See also rostellum.

2. (Arthropoda: Chelicerata) The labrum of spiders.

3. (Arthropoda: Crustacea) The median pointed process at the end of the cephalothorax. a. In thoracic barnacles, a valve between the lateral and opposite carina at the basiscutal end of the capitulum; simple and bearing alae in many balanomorphs, but compound and overlapping the laterals in higher balanomorphs. See also compound rostrum.

4. (Arthropoda: Insecta) a. In Hemiptera, the beak. b. In Coleoptera scarab beetles, a rigid, ventral extension of the paramere.

5. (Brachiopoda) Inner elevation of the brachial valve; a pair of club shaped elevations for muscle attachment for the brachial protractor muscles.

6. (Mollusca: Cephalopoda) a. The anteriormost point of the upper and lower mandibles

See also: beak. b. The spine anchored on the posterior end of a cuttle bone and some pens. 7. (NEMATA: Secernentea) In Aphelenchida males, the beak-like projection ventrad near the proximal end of the spicule, joining the dorsal and ventral spicular shafts.