A Dense Epizoobiontic Infestation of a Lower Carboniferous Crinoid (Amphoracrinus gilbertsoni (Phillips)) by Oichnus paraboloides Bromley

A variety of pits representing symbiotic embedments, sometimes associated with pathological deformation in the host, are known from the skeletons of Paleozoic stalked echinoderms. These structures are well known from multiple genera of crinoids and a limited number of blastozoans but have not previously been described in detail from the skeletons of rhombiferans. This is surprising given the abundance of rhombiferans in certain deposits, the co-occurrence of rhombiferans with frequently infested taxa, including diploporitans, in multiple assemblages, and the morphological similarity between certain rhombiferan taxa and coeval infested crinoids. The common hemicosmitid rhombiferan Caryocrinites Say, 1825 is widespread throughout the middle Silurian of eastern North America and is herein reported to contain symbiotic (potentially parasitic) embedment structures. Specimens were collected from the lower portion of the mudstone lithofacies of the Massie Formation (Wenlock, Sheinwoodian) at the Napoleon quarry of southeastern Indiana, USA. Strong host specificity is indicated by the absence of pits in C. ornatus Say, 1825 and exclusive infestation of a smaller co-occurring species of Caryocrinites. Thecae with embedment structures are consistently smaller than thecae without such structures, with pitted specimens being restricted to a narrow range of thecal heights (20–24 mm). All embedment structures are present only on the proximal portion of thecae, with individual specimens containing between one and 30 pits. No elevated rims or significant swelling were observed on any specimens, and all pits are relatively small (~1 mm in diameter). The presence of symbiotic embedment structures represents an additional example of a crinoid-like aspect to the ecology of Caryocrinites.

Section: Discussionsupporting

confidence: 82%

Section: Discussionsupporting

confidence: 82%

Symbiotic embedment structures in Silurian Caryocrinites (Echinodermata, Rhombifera, Hemicosmitida)

Thomka

Brett

Bissett³

2020

“…Several examples included in Sedilichnus (such as material included in the original description of Tremichnus) exhibit evidence of a reaction by the host organism to activity of the epizoan taxon (Brett, 1985). These include galls, stereom swellings, bioclaustrations and embedment structures (Brett, 1985;Tapanila, 2005;Donovan et al, 2006). Following the precedence set by other workers, these deformities on the host taxon's skeletal test or shell are not considered to be viable ichnotaxobases Bromley, 2004;Bertling et al, 2006).…”

Section: Systematic Paleontologymentioning

confidence: 99%

Sedilichnus, Oichnus, Fossichnus, and Tremichnus: ‘Small Round Holes in Shells’ Revisited

Zonneveld¹,

Gingras²

2014

Small round pits and holes in fossil skeletal material are found in a wide variety of invertebrate substrates from diverse environmental settings. They are associated with parasitism, predation and commensal attachment. Four ichnogenera have been proposed for these trace fossils:SedilichnusMüller,OichnusBromley,TremichnusBrett andFossichnusNielsen, Nielsen and Bromley. Previous authors have established thatTremichnusis a junior synonym ofOichnus. Herein we show thatOichnusandFossichnusare junior synonyms ofSedilichnus.Sedilichnus, as defined herein, includes 10 ichnospecies.Sedilichnus spongiophilus, S. simplex, S. paraboloides, S. ovalis, S. coronatus, S. gradatus, S. halo, S. asperus, S. excavatusandS. solus. Consistent with previous workSedilichnusichnospecies are defined solely by morphological criteria and not by a priori assumptions regarding depositional environment or tracemaker. Thus, this ichnotaxon is recognized in both marine and continental settings on a wide variety of invertebrate skeletal tests. As is true with many ichnotaxa,Sedilichnusichnospecies represent end-members in morphological spectra, however each ichnospecies is clearly differentiable from the others.Sedilichnus spongiophilusare circular, non-penetrative pits in shells.Sedilichnus paraboloidesare penetrative holes with spherical paraboloid forms and typically have larger external openings and smaller internal openings.Sedilichnus simplexare simple cylindrical borings that have both penetrative and non-penetrative forms.Sedilichnus coronatusdiffer from other forms by the presence of an etched or granular halo surrounding the boring.Sedilichnus gradatushave two concentric parts, an outer boring and an inner shelf of smaller diameter.Sedilichnus ovalisandS. asperusare both oval in outline differing in the presence of tapering paraboloid margins inS. ovalisand margins perpendicular to the substrate inS. asperus.Sedilichnus excavatusandS. solusare primarily non-penetrative and differ from otherSedilichnusby the presence of central, raised bosses or platforms. These two ichnospecies differ in the shapes of their external walls and the proportional thickness of the bounding groove.

“…5.6) resulted in plate interruption and are surrounded by a bulge. Oichnus is known to occur on crinoids (e.g., Brett, 1985;Donovan et al, 2006;Donovan and Lewis, 2010;Wilson et al, 2010), so its presence on this crinoid is not surprising.…”

Section: Lutocrinus Boliviaensis New Speciesmentioning

confidence: 99%

Echinoderms from the Lower Devonian (Emsian) of Bolivia (Malvinokaffric Realm)

Thompson

Ausich

Smith³

2013

Crinoid faunas from the Lower Devonian of South America are poorly known. Two new taxa are described from the Emsian Icla Formation at Cerro Kochis in the Cochabamba Department: the rhodocrinitid, Lutocrinus boliviaensis n. gen. n. sp. and Griphocrinus pirovanoi n. sp. Two additional camerates are reported from the Emsian Belèn Formation of the Altiplano region in the La Paz Department, including Ctenocrinus branisai n. sp. and Boliviacrinus isaacsoni McIntosh, 1988. In addition, a specimen of the blastoid, Pachyblastus dicki Bremier and Macurda, 1972, was recovered from the Altiplano region. These crinoids and material previously collected by Leonardo Branisa, including specimens of C. branisai n. sp., Apurocrinus sucrei McIntosh, 1981, B. isaacsoni McIntosh, 1988, and L. boliviaensis n. sp., are described and revised. The specimens give new insights into the Lower Devonian Malvinokaffric Realm of Bolivia, a relatively new frontier in crinoid paleontology.