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The first Cretaceous ophiopluteus skeleton (Echinodermata: Ophiuroidea)

Published online by Cambridge University Press:  28 July 2021

Mike Reich*
Affiliation:
SNSB—Bavarian State Collection of Palaeontology and Geology, Richard-Wagner-Straße 10, 80333 Munich, Germany Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Richard-Wagner-Straße 10, 80333 Munich, Germany GeoBio-Center, Ludwig-Maximilians-Universität München, Richard-Wagner-Straße 10, 80333 Munich, Germany

Abstract

Larvae of sea urchins, brittle stars, and allies are common, ecologically important, and diverse members of marine ecosystems in all of the world's oceans today. In contrast to modern representatives, the fossil record of echinoderm larvae is poorly known. This study reports the first ophiopluteus skeleton from Cretaceous sediments worldwide, obtained from chalky sediment of the Isle of Wolin, NW Poland. The evidence presented here, that it is possible to isolate fossil echinoderm larval skeletons from rocks, indicates a hidden diversity of such fragile fossils and thus the possibility of direct geological recording.

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Type
Articles
Copyright
Copyright © The Author(s), 2021. Published by Cambridge University Press on behalf of The Paleontological Society
Figure 0

Figure 1.Modern echinoderm larvae. All polarized light micrographs (crossed nicols). (1) Bipinnaria (Asteroidea); larval stage of Asterias rubens (Linnaeus, 1758) (ZMUC TM-F/45)—Strib, Kattegat (collected in 1879). (2) Auricularia (Holothuroidea); giant larva ‘Auricularia nudibranchiata Chun’; larval stage of Protankyra brychia (Verrill) (ZMUC TM-F/36)—Misaki, Sagami Bay (collected in 1899). (3) Fully formed echinopluteus (Echinoidea); larval stage of Heterocentrotus mamillatus (Linnaeus, 1758) (ZMUC TM-F/51)—Hurghada, Red Sea (collected in 1936). (4) Six-armed ophiopluteus (Ophiuroidea) [‘Ophiopluteus mancus Mortensen’]; larval stage of Amphiura filiformis (O.F. Müller, 1776) (ZMUC TM-E/86)—Kristineberg, Gullmarfjord (collected in 1918). (5) Not fully formed ophiopluteus (Ophiuroidea); larval stage of Macrophiothrix propinqua (Lyman, 1861) (ZMUC TM-E/100)—Hurghada, Red Sea (collected in 1936). Note wheel-shaped ossicles of holothuroid auricularia (2) and skeletal rods in plutei (3–5). All specimens from (permanent) microscopic slides mounted with Canada Balsam stored in T. Mortensen collection at ZMUC. Abbreviations in white letters: fr = fenestrated skeletal rods; ufr = unfenestrated skeletal rods; lwo = larval wheel ossicles. Abbreviations in black letters: al = anterolateral rod; b = body rod; da = dorsal arch; e = end rod; pd = posterodorsal rod; pl = posterolateral rod; po = postoral rod; pr = preoral arm; ptr = posterior transverse rod; r = recurrent rod; tr = transverse rod; vtr = ventral transverse rod. Scale bar = 500 μm.

Figure 1

Figure 3.Summary of fossil record of modern echinoderm larvae (Crinoidea, Asteroidea, Ophiuroidea, Echinoidea, Holothuroidea), based on data presented in Table 1. Gray vertical bar in Lower Cretaceous (ca. 110 Ma) highlights first appearance of representatives of Ophiuridae (Ophiurida), Ophiocomidae (Ophiacanthida), Amphiuridae, Ophiactidae, and Ophiotrichidae (latter all Amphilepidida; systematics after O'Hara et al., 2017)—modern ophiuroid families in which ophioplutei occur. Stratigraphic position of first Cretaceous ophiopluteus described herein indicated by (red) asterisk.

Figure 2

Table 1.Fossil larval skeletons of modern echinoderm representatives reported in the scientific literature (in stratigraphic order, revisions included).

Figure 3

Figure 2.Late Cretaceous ophiopluteus in comparison with modern body skeletons. (1–3) Ophiopluteus, gen. and sp. A, right part of body skeleton (SNSB-BSPG 2020 XXXIX 5) from late Turonian chalk of Kępa, Isle of Wolin, NW Poland: (1) inner view; (2) inner oblique view; (3) lateral oblique view. Note small thorns at rods (black arrows). All scanning electron micrographs (specimen covered with coccoliths in part). (4, 5) ‘Ophiopluteus arcifer’ Mortensen, 1921, Recent (linked adult species unknown), compound body skeleton (left part = light gray; right part = dark gray; median processes = white) reported from Gulf of Siam, Strait of Malacca, and off Jolo, Philippines (modified from Mortensen, 1921). Abbreviations: al = anterolateral rod; b = body rod; dm = dorsal median process; dr = dorsal recurrent rod; dtr = dorsal transverse rod; e = end rod; pd = posterodorsal rod; pl = posterolateral rod; po = postoral rod; vm = ventral median process; vr = ventral recurrent rod; vtr = ventral transverse rod.. Scale bars = 50 μm (1–3), and 100 μm (4, 5).