Novel mode of postembryonic development in &lt;em&gt;Ammothea&lt;/em&gt; genus (Pycnogonida: Ammotheidae) from Antarctic waters

Esperanza Cano,Pablo J López-González

doi:10.3989/scimar.2009.73n3541

Abstract

In this paper the postembryonic development of Ammothea glacialis (family Ammotheidae) is described. The studied material was collected during the Italica XIX cruise to Victoria Land, Ross Sea, Antarctica. The external morphology of three larval instars is described and illustrated. The development of A. glacialis has the following characteristics: (1) protonymphon hatch from the eggs; (2) the larvae have yolk reserves and relatively large size (0.7 mm in length); (3) the larvae remain on the ovigerous legs of males during several moults; (4) the larvae have reduced larval II-III appendages and the spinning apparatus is absent; (5) the development of walking legs is sequential. This development is compared with those previously known, especially with Propallene longiceps and Nymphon grossipes.

Highlights

The pycnogonids, or sea spiders, which can be found in all marine habitats ranging from the intertidal zone to abyssal depths, are distributed worldwide, and range in size from less than 1 mm to over 70 cm in leg span (Hedgpeth, 1947; Arnaud and Bamber, 1987)
Cano and P.J. lópez-González of larval appendages), in some cases the eggs directly hatch as postlarval stage because protonymphons evolute completely into the egg shell (Bamber, 2007)
In the last embryonic phase the embryo differentiates three pairs of larval appendages, with spination, and a proboscis develops around the stomodeum; the embryo becomes a protonymphon larva (Arnaud and Bamber, 1987)

Summary

Introduction

The pycnogonids, or sea spiders, which can be found in all marine habitats ranging from the intertidal zone to abyssal depths, are distributed worldwide, and range in size from less than 1 mm to over 70 cm in leg span (Hedgpeth, 1947; Arnaud and Bamber, 1987).In pycnogonids a series of courtship and mating behaviours have been observed during which the female lays the eggs and transfers them to the male’s oviger appendages. Fertilisation is external: the male fertilises the eggs once they have been placed into his care, and glues them to the oviger, forming compact egg masses. He carries the eggs around until they hatch, but in several cases he continues to carry the larvae after hatching during part of their postlarval development (Wilhelm et al, 1997; Bain and Govedich, 2004). Cano and P.J. lópez-González of larval appendages), in some cases the eggs directly hatch as postlarval stage because protonymphons evolute completely into the egg shell (Bamber, 2007)

Methods

Results

Discussion

Conclusion