Sea Urchin Covering Behavior: A Comparative Review

Abstract

Covering behavior in sea urchins is an important aspect of many species' ecology and has a variety of perceived benefits including food source, mechanical defense, shielding from sunlight, and predator protection. The goal of this study was to determine whether an urchin genus's main benefit from this form of crypsis is correlated with either phylogenetic relationships or environmental factors (ocean depth and climate). To evaluate this hypothesis, a literature review was conducted on 15 urchin genera that use the covering reaction. The function of this behavior for the aforementioned genera was both mapped onto a phylogeny and evaluated, based on the climate and depth of the genera's habitats to determine whether the patterns exist. The results suggest that phylogenetic relationships provide a more functional predictive tool for determining the purpose of covering in an urchin genus than its environment. This conclusion is useful for understanding the biology of sea urchins as well as how the covering reaction relates to the many other cryptic behaviors used by animal species.

Population Density, Size Structure, and Reproductive Cycle of the Comestible Sea Urchin Sphaerechinus granularis (Echinodermata: Echinoidea) in the Pagasitikos Gulf (Aegean Sea)

“…According to distance sampling density estimations, biases are typically due to the movement of the target species or random errors [ 18 , 24 ]. As S. granularis is a sedentary species, its motility patterns cannot bias density estimations (i.e., moving faster than the observer does), and so, relevant differences are most probably related with its cryptic behavior, i.e., active covering of the test with shells, pebbles, and algae [ 8 ]. The possibility of overlooking those well-hidden sea urchin individuals during underwater surveys, especially in vegetated bottoms, is increasing.…”

“…Its bathymetric distribution expands from the intertidal down to 130 m depth [ 6 ], but it is most usually found in the shallow sublittoral (5 to 15 m) where it forms locally dense populations [ 7 ]. As other sea urchins, it manifests a cryptic behavior ( Figure 1 ) by occupying crevices and by camouflaging, as it covers its test with shell fragments, pebbles, and algae [ 8 ].…”

Planktonic sea urchin larvae change their swimming direction in response to strong photoirradiation

“…Opsin2 and Opsin5 have been found only in echinoderms; therefore, they are thought to be specific to the group. Because some of the expression patterns of these genes have been reported in both embryos/larvae and adults [ 24 – 27 ], it is reasonably expected that sea urchins have the ability to react to light stimuli from a genomic perspective, as reported in adult behavioral studies [ 28 , 29 ]. However, the functions of photoreceptor genes have never been confirmed by using genetic modification except for the function of the recently reported gut-regulatory Go-Opsin [ 12 ], and the neural pathway regulating cilia-based larval behavior has not yet been identified.…”

Characterization of thyrotropin-releasing hormone producing neurons in sea urchin, from larva to juvenile

“…Distribution of serotonergic cells (shown in magenta) in relations to TRHergic cells (in green) in the different sea urchin species, based on findings of this study or deduced from previous studies ( Bisgrove and Raff, 1989 ; Byrne et al, 2007 ; Rendell-Bhatti et al, 2021 ; Tsironis et al, 2021 ). The phylogenetic relationships between the four sea urchin species were deduced from Littlewood and Smith (1995) and Ziegenhorn (2017) .…”