Allometric growth in the extant coelacanth lung during ontogenetic development.

Camila Cupello,Paulo M Brito,Gaël Clément,Hugo Dutel,Marc Herbin,François J Meunier,Philippe Janvier

doi:10.1038/ncomms9222

Abstract

Coelacanths are lobe-finned fishes known from the Devonian to Recent that were long considered extinct, until the discovery of two living species in deep marine waters of the Mozambique Channel and Sulawesi. Despite extensive studies, the pulmonary system of extant coelacanths has not been fully investigated. Here we confirm the presence of a lung and discuss its allometric growth in Latimeria chalumnae, based on a unique ontogenetic series. Our results demonstrate the presence of a potentially functional, well-developed lung in the earliest known coelacanth embryo, and its arrested growth at later ontogenetic stages, when the lung is clearly vestigial. The parallel development of a fatty organ for buoyancy control suggests a unique adaptation to deep-water environments. Furthermore, we provide the first evidence for the presence of small, hard, flexible plates around the lung in L. chalumnae, and consider them homologous to the plates of the ‘calcified lung' of fossil coelacanths.

Highlights

Coelacanths are lobe-finned fishes known from the Devonian to Recent that were long considered extinct, until the discovery of two living species in deep marine waters of the Mozambique Channel and Sulawesi
L. chalumnae does not possess a calcified organ in its abdominal cavity, but a short oesophageal diverticulum surrounded by a fatty organ
This so-called ‘fatty organ’[10,20], previously referred in the literature as a swimbladder[21], air bladder[4], fatty lung[20] and modified lung or bladder[22], has a ventral position relative to the oesophagus, turns dorsally relative to the stomach and reaches the posterior wall of the abdominal cavity[10]. This organ in Latimeria is structurally different from the swimbladder of many actinopterygians that is, in the latter group, an air sac with, or without, an anterior opening located on the dorsal side of the oesophagus

Summary

Introduction

Coelacanths are lobe-finned fishes known from the Devonian to Recent that were long considered extinct, until the discovery of two living species in deep marine waters of the Mozambique Channel and Sulawesi. Latimeria is a heavily built fish living in rocky environments between 110 and 400 m deep in the coastal waters of the Mozambique Channel and of Sulawesi[12,13,14] This large animal (up to 2 m long) is ovoviviparous[15]. The presence of a large calcified sheath in the abdominal cavity of fossil coelacanths has been known since the 19th century[18,19] but was previously regarded as either an ‘internal osseous viscus’ (unknown internal organ), a bladder or swimbladder. Many aspects of the anatomy and the development of these structures in Latimeria remain unclear, as well as their homology to the calcified organ of many fossil coelacanths

Methods

Results

Conclusion