Fornshell J.A. 2015. Larval stages of two deep sea pycnogonids // Invertebrate Zoology. Vol.12. No.2: 197–205 [in English].
Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington DC, USA. E-mail: email@example.com
ABSTRACT. The larvae of two species of sea spiders in the archived collections of the Smithsonian Institution’s National Museum of Natural History (NMNH) are described: the first three instars of Ammothea allopodes Fry et Hedgpeth 1969, and one late post-hatching stage of Nymphon tenellum (Sars, 1888). Ammothea allopodes larval stages are examples of a typical protonymphon larva. The single stage of N. tenellum does not fit into any of the five recognized larval developmental patterns; it displays characteristics of an attaching larva, an encysting larva and a typical protonymphon larva. These characteristics are: (1) 3-segmented larval appendages I, II and III; (2) underived buds of appendages IV–VI, walking legs 1, 2 and 3, present; (3) the digestive tract is incomplete, there is no proctodeum present; and (4) a large amount of yolk is present. A new developmental pattern is proposed for this larval stage.
KEY WORDS: Pycnogonida, protonymphon larva, larval stages.