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A "protective shell" around the larval cocoon of Cephalodiscus densus Andersson, 1907 (Graptolithoidea, Hemichordata)

S.Schiaparelli, R. Cattaneo-Vietti and P. Mierzejewski

Polar Biology 2004
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Within the framework of the Italian XVII PNRA expedition (austral summer 2001-2002), several colonies of the Graptolithoidea (=Pterobranchia + Graptolithina) species, Cephalodiscus densus Andersson and C. hodgsoni Ridewood, were collected by trawl from Tethys Bay (Terra Nova Bay, Ross Sea). These organisms were maintained in aquaria for 2 weeks and their behaviour observed. The dissection of some colonies of C. densus allowed the reconstruction of the eggs fate and the documentation of the formation of a protective shell around the cocoons of larvae settled within "parental" colony encasement.
The shell is produced by cementing size-selected debris, either of organic or inorganic origin, accumulated inside the encasement. This is the first documentation of such a structure within living Hemichordata and it helps to reinterpret some of the "resting structures" within zooidal tubes or thecae of particularly well-preserved fossil graptolites.
Edited by

Piotr Mierzejewski, the Count of Calmont and Countess Maja A. Korwin-Kossakowska

SEM micrographs of protective shells around the cocoons of Cephalodiscus densus larvae.
From Schiaparelli et al.