Premium
The Heart Ultrastructure in Two Species of Pycnogonids, and its Phylogenetic Implications
Author(s) -
TJØNNELAND AUDFINN,
KRYVI HARALD,
OSTNES JAN PERRY,
ØKLAND STEINAR
Publication year - 1985
Publication title -
zoologica scripta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.204
H-Index - 64
eISSN - 1463-6409
pISSN - 0300-3256
DOI - 10.1111/j.1463-6409.1985.tb00191.x
Subject(s) - biology , endocardium , ultrastructure , sarcomere , anatomy , microbiology and biotechnology , medicine , myocyte
The heart of the pycnogonids Nymphon (Chaetonymphon) macronyx G. O. Sars and Boreonymphon cf. abyssorum Norman is pseudotubular and lacks an epicardium and an endocardium. The body wall forms the roof over the heart lumen. The myocardium is innvervated, and forms the lateral walls of the heart. Myofibres are absent in the midventral floor. This part is formed by cells of the horizontal septum attached to the gut complex. The myofibres are short. Interdigitating intercalated discs have not been observed, but lateral overlaps are common. Z‐, I‐ and A‐bands are seen in the sarcomere. The 2‐bands are diffuse and irregular. The sarcolemma invaginates and forms a sparse system of clefts; a poorly developed T‐system is indicated. Its presence supports the view that a T‐system is inherent in the arthropod myocardium. Couplings are not related to any specific sarcomere band level. It is implied that the thin‐walled pseudotubular heart in pycnogonids is a result of a reduction, and that it functions more like a channel than a heart.