Evolutionary morphology of the antennal heart in stick and leaf insects (Phasmatodea) and webspinners (Embioptera) (Insecta: Eukinolabia)

Jörg Hammel,Sven Bradler,Benjamin Wipfler,Günther Pass,Bernd R Müller,Sebastian Büsse

doi:10.1007/s00435-021-00526-4

Abstract

The morphology of the antennal hearts in the head of Phasmatodea and Embioptera was investigated with particular reference to phylogenetically relevant key taxa. The antennal circulatory organs of all examined species have the same basic construction: they consist of antennal vessels that are connected to ampullae located in the head near the antenna base. The ampullae are pulsatile due to associated muscles, but the points of attachment differ between the species studied. All examined Phasmatodea species have a Musculus (M.) interampullaris which extends between the two ampullae plus a M. ampulloaorticus that runs from the ampullae to the anterior end of the aorta; upon contraction, all these muscles dilate the lumina of both ampullae at the same time. In Embioptera, only the australembiid Metoligotoma has an M. interampullaris. All other studied webspinners instead have a M. ampullofrontalis which extends between the ampullae and the frontal region of the head capsule; these species do not have M. ampulloaorticus. Outgroup comparison indicates that an antennal heart with a M. interampullaris is the plesiomorphic character state among Embioptera and the likely ground pattern of the taxon Eukinolabia. Antennal hearts with a M. ampullofrontalis represent a derived condition that occurs among insects only in some embiopterans. These findings help to further clarify the controversially discussed internal phylogeny of webspinners by supporting the view that Australembiidae are the sister group of the remaining Embioptera.

Highlights

The circulatory system of insects serves a multitude of vital transport functions within the body, including those of molecules, hemocytes, or thermal energy
The anterior end of the aorta is located behind the brain and the outpouring hemolymph flows through a kind of channel, formed by the brain, the circumesophageal connectives, and the pharynx, into the hemocoelic space in front of the supraesophageal ganglion
There are some incomplete and unillustrated descriptions of the antennal heart muscles of Phyllium philippinicum, Sipyloidea sipylus and Agathemera crassa (Wipfler et al 2011). These descriptions are consistent with respect to the presence of paired ampullae with antennal vessels having a uniform wall and two muscles associated with the antennal heart ampulla: The unpaired

Summary

Introduction

The circulatory system of insects serves a multitude of vital transport functions within the body, including those of molecules, hemocytes, or thermal energy (reviews: Hertel and Pass 2002; Hillyer and Pass 2020; Jones 1977; Miller 1985; Miller and Pass 2009; Wirkner and Richter 2010; Wirkner et al 2013). Zoomorphology (2021) 140:331–340 or were reduced and independent accessory circulatory organs evolved to ensure hemolymph supply of the various body appendages These can be either simple guiding structures that passively lead the hemolymph flow through these appendages, or accessory pulsatile organs which function as autonomous auxiliary hearts that actively pump hemolymph through these appendages (reviews: Pass 1998, 2000; Pass et al 2006; Wirkner et al 2013). Many of these circulatory organs are evolutionary novelties of pterygote insects, which make them prime examples to investigate the poorly understood topic of the origin of novel organs (Pass 2000; Pass et al 2015)

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Conclusion