skip to main content


Title: Organization of the subumbrellar musculature in the ephyra, juvenile, and adult stages of Aurelia aurita Medusae
Abstract

We used fluorescently labeled phalloidin to examine the subumbrellar musculature of the scyphozoan jellyfishAurelia auritain a developmental series from ephyra to adult medusa. In the ephyra, the swim musculature includes a disc‐like sheet of circular muscle, in addition to two radial bands of muscle in each of the eight ephyral arms. The radial muscle bands join with the circular muscle, and both circular and radial muscle act together during each swim contraction. As the ephyra grows into a juvenile medusa, arms tissue is resorbed as the bell tissue grows outward, so eventually, the ephyral arms disappear. During this process, the circular muscle disc also grows outward and the radial muscle bands of the arms also disappear. At this time, a marginal gap appears at the bell margin, which is devoid of circular muscle cells, but has a loose arrangement of radial muscle fibers. This marginal gap is preserved as the medusa grows, and contributes to the floppy nature of the bell margin. Radial distortions in the circular muscle layer involve muscle fibers that run in random directions, with a primarily radial orientation. These are believed to be remnants of the radial muscle of the ephyral arms, and the distortions decrease in number and extent as the medusa grows. Since the mechanics of swimming changes from drag‐based paddling in the ephyra to marginal rowing in the adult medusa, the development of the marginal gap and the presence of radial distortions should be considered in terms of this mechanical transition.

 
more » « less
PAR ID:
10460780
Author(s) / Creator(s):
 ;  ;  ;  
Publisher / Repository:
Wiley-Blackwell
Date Published:
Journal Name:
Invertebrate Biology
Volume:
138
Issue:
3
ISSN:
1077-8306
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    The locomotory musculature of the pteropodClione limacinaincludes slow‐twitch, fatigue‐resistant muscle fibers and fast‐twitch fatigable fibers. Dorsal musculature produces a dorsal bend of the wing, while ventral musculature produces a ventral bend. During the change to fast swimming, ~10% of the slow‐twitch fibers, including both dorsal and ventral fibers, exhibit fast repetitive firing that greatly exceeds the in‐phase excitation of the appropriate wing musculature. The normal wing‐beat frequency for fast swimming is 2–4 Hz, while repetitive firing occurs at 11 Hz. A component of fast‐swimming control is excitation of Pd‐SWneurons of the pedal ganglion. These cells are serotonin immunoreactive, and they innervate the slow‐twitch musculature of the wing. Induced excitation of a Pd‐SWneuron was capable of triggering repetitive firing in some slow‐twitch muscle cells. Repetitive firing in a subset of muscle fibers of the swim musculature could represent a contribution to wing stiffening, which has been documented to occur during the change to fast swimming.

     
    more » « less
  2. Abstract

    The contractile protein myosinIIis ubiquitous in muscle. It is widely accepted that animals express tissue‐specific myosin isoforms that differ in amino acid sequence andATPase activity in order to tune muscle contractile velocities. Recent studies, however, suggested that the squidDoryteuthis pealeiimight be an exception; members of this species do not express muscle‐specific myosin isoforms, but instead alter sarcomeric ultrastructure to adjust contractile velocities. We investigated whether this alternative mechanism of tuning muscle contractile velocity is found in other coleoid cephalopods. We analyzed myosin heavy chain transcript sequences and expression profiles from muscular tissues of a cuttlefish,Sepia officinalis, and an octopus,Octopus bimaculoides, to determine if these cephalopods express tissue‐specific myosin heavy chain isoforms. We identified transcripts of four and six different myosin heavy chain isoforms inS. officinalisandO. bimaculoidesmuscular tissues, respectively. Transcripts of all isoforms were expressed in all muscular tissues studied, and thusS. officinalisandO. bimaculoidesdo not appear to express tissue‐specific muscle myosin isoforms. We also examined the sarcomeric ultrastructure in the transverse muscle fibers of the arms ofO. bimaculoidesand the arms and tentacles ofS. officinalisusing transmission electron microscopy and found that the fast contracting fibers of the prey capture tentacles ofS. officinalishave shorter thick filaments than those found in the slower transverse muscle fibers of the arms of both species. It thus appears that coleoid cephalopods, including the cuttlefish and octopus, may use ultrastructural modifications rather than tissue‐specific myosin isoforms to adjust contractile velocities.

     
    more » « less
  3. Cycloneuralians are ecdysozoans with a fossil record extending to the Early Cambrian Fortunian Age and represented mostly by cuticular integuments. However, internal anatomies of Fortunian cycloneuralians are virtually unknown, hampering our understanding of their functional morphology and phylogenetic relationships. Here we report the exceptional preservation of cycloneuralian introvert musculature in Fortunian rocks of South China. The musculature consists of an introvert body-wall muscular grid of four circular and 36 radially arranged longitudinal muscle bundles, as well as an introvert circular muscle associated with 19 roughly radially arranged, short retractors. Collectively, these features support at least a scalidophoran affinity, and the absence of muscles associated with a mouth cone and scalids further indicates a priapulan affinity. As in modern scalidophorans, the fossil musculature, and particularly the introvert circular muscle retractors, may have controlled introvert inversion and facilitated locomotion and feeding. This work supports the evolution of scalidophoran-like or priapulan-like introvert musculature in cycloneuralians at the beginning of the Cambrian Period.

     
    more » « less
  4. ABSTRACT

    Chemical Cartography, or mapping, of our Galaxy has the potential to fully transform our view of its structure and formation. In this work, we use chemical cartography to explore the metallicity distribution of OBAF-type disc stars from the LAMOST survey and a complementary sample of disc giant stars from Gaia DR3. We use these samples to constrain the radial and vertical metallicity gradients across the Galactic disc. We also explore whether there are detectable azimuthal variations in the metallicity distribution on top of the radial gradient. For the OBAF-type star sample from LAMOST, we find a radial metallicity gradient of Δ[Fe/H]/ΔR ∼−0.078 ± 0.001 dex kpc−1 in the plane of the disc and a vertical metallicity gradient of Δ[Fe/H]/ΔZ ∼−0.15 ± 0.01 dex kpc−1 in the solar neighbourhood. The radial gradient becomes shallower with increasing vertical height, while the vertical gradient becomes shallower with increasing Galactocentric radius, consistent with other studies. We also find detectable spatially dependent azimuthal variations on top of the radial metallicity gradient at the level of ∼0.10 dex. Interestingly, the azimuthal variations appear be close to the Galactic spiral arms in one data set (Gaia DR3) but not the other (LAMOST). These results suggest that there is azimuthal structure in the Galactic metallicity distribution and that in some cases it is co-located with spiral arms.

     
    more » « less
  5. Abstract

    Scyphomedusae are widespread in the oceans and their swimming has provided valuable insights into the hydrodynamics of animal propulsion. Most of this research has focused on symmetrical, linear swimming. However, in nature, medusae typically swim circuitous, nonlinear paths involving frequent turns. Here we describe swimming turns by the scyphomedusaAurelia auritaduring which asymmetric bell margin motions produce rotation around a linearly translating body center. These jellyfish ‘skid’ through turns and the degree of asynchrony between opposite bell margins is an approximate predictor of turn magnitude during a pulsation cycle. The underlying neuromechanical organization of bell contraction contributes substantially to asynchronous bell motions and inserts a stochastic rotational component into the directionality of scyphomedusan swimming. These mechanics are important for natural populations because asynchronous bell contraction patterns are commonin situand result in frequent turns by naturally swimming medusae.

     
    more » « less