The Silurian myodocope ostracodeEntomozoefrom the Pentland Hills, Scotland: its taxonomic, ecological and phylogenetic significance and the affinity of the bolbozoid myodocopes

Abstract

The monotypic ostracodeEntomozoe(pro Entomis) (Superorder Myodocopa) from the Silurian of Scotland, type genus of the Entomozoidae, is revised for the first time since being established in 1861. Based on the type and new collections ofEntomozoe tuberosa(Jones, 1861), the genus shows affinity to bolbozoid myodocopes rather than to forms hitherto universally considered as ‘typical’ entomozoid myodocopes. The families Entomozoidae and Bolbozoidae are considered synonymous. In the interests of stability of nomenclature, in particular to preserve the traditionally understood usage of the taxon Entomozoidae, a case must be made to the International Commission on Zoological Nomenclature to set aside any previous designations and to establish a new type-species forEntomozoe.Entomozoe, from the Llandovery Series, is the earliest known myodocope in the fossil record. It occurs as part of a low diversity, shallow water, nearshore assemblage. In contrast to other, but younger, Silurian bolbozoid myodocopes, it is probably a benthic form. The differences in the anterior shell morphology of Silurian bolbozoid taxa possibly reflect changes both in soft-part morphology and from benthic to pelagic lifestyles within the group.Both bolbozoid and ‘entomozoid’ myodocopes are assigned to the Order Myodocopida rather than to the Order Halocypridida, though the taxonomic affinity of the ‘entomozoids’ is, at best, uncertain.

Silurian Myodocopes: Pioneer pelagic ostracods and the chronology of an ecological shift

“…Moreover, in order to appropriately place such myodocopes within the established context of ostracod studies we compare them herein with another group of Silurian ostracods that have been well studied and are regarded as benthic, namely the ubiquitous palaeocopes and in particular the superfamily Beyrichiacea. Furthermore, in reviewing the worldwide spatial and chronological occurrence of Silurian myodocopes we also support the idea (Siveter & Vannier 1990) that there is evidence for a possible ecological shift of myodocope stock actually during that time period -a shift which is charted in a change from a benthic to pelagic mode of life and from relatively shallow nearshore/shelf habitats to somewhat deeper and relatively more outer/off-shelf environments.…”

“…'Typical Silurian myodocopes' are herein taken to include representatives of two families, the Cypridinidae and Bolbozoidae, and to exclude members of what traditionally have been regarded (but see Siveter & Vannier 1990) as 'Entomozoacea'. Bolbozoids and cypridinids are relatively large ostracods (adults 1-15mm long) with very distinctive morphological features, such as the presence of a rostrum and associated rostra1 incisure at the anterior margin of the valve and (in the case of bolbozoids) a prominent anterodorsal valve bulb (Siveter 1984;Siveter, Vannier & Palmer 1987;Siveter & Vannier 1990).…”

An exceptionally preserved myodocopid ostracod from the Silurian of Herefordshire, UK

“…figure 1a,l ). The subcircular lateral outline combined with a long, tapered rostrum and associated well-developed rostral incisure, together with the presence of a well-developed caudal siphon, recall other myodocopid families, especially cypridinids (supposed Silurian to Recent) and others such as bolbozoids and entomochonchids, which are known only from the Palaeozoic (Siveter & Vannier 1990;Kornicker & Sohn 2000). In limb morphology, subcircular lateral valve outline and the presence of a caudal siphon, N. flata is also like the Sarsiellidae (no known fossil representatives), but such a prominent rostrum and especially a deep rostral incisure are not typical of that family.…”

Middle Katian/lowermost Hirnantian ostracods from the Prague Basin (Czech Republic): Diversity responses to the climatic changes

“…-Our specimen shows some of the typical features of the predominantly Silurian genus Entomozoe Přibyl, 1950, the assignment of which to ostracods is doubtful (for different opinions on the systematic position of the genus see Vannier 1990 andAbe 1992).…”