Pedum spondyloideum

{{Short description|Species of bivalve}} {{Speciesbox | image = Pedum spondyloideum.jpg | image_caption = | genus = Pedum (bivalve) | grandparent_authority = Bronn, 1862 | parent_authority = Bruguière, 1792 | species = spondyloideum | authority = (Gmelin, 1791) | display_parents = 3 | synonyms = * Hinnitinae Habe, 1977 * Peduminae T. Habe, 1977 <small>'''Species synonymy'''</small> {{collapsible list| *''Ostrea pedum'', Röding, 1798 *''Ostrea spondyloidea'', Gmelin, 1791 *''Pedum pedum'' *''Pedum pedum intensum'', Iredale, 1939 }} | synonyms_ref = <ref>{{Cite WoRMS|title=Pedinae Bronn, 1862|id=510739|access-date=2026-01-24}}</ref><ref name="WoRMS">{{cite WoRMS |title=''Pedum'' |id=204913 |access-date=31 August 2022}}</ref> }}

'''''Pedum''''' is a monotypic genus of bivalves belonging to the family Pectinidae, the scallops. The only species is '''''Pedum spondyloideum''''' and it is the only genus in the tribe '''Pedini'''.<ref name="WoRMS"/> Sometimes referred to as the '''iridescent scallop''',<ref>{{cite web |title=Iridescent Scallop Pedum spondyloideum |url=https://www.inaturalist.org/taxa/202181-Pedum-spondyloideum |website=iNaturalist.org |publisher=iNaturalist |access-date=24 January 2026}}</ref> this species is found throughout the Indo-Pacific.<ref name="GBIF">{{GBIF|id=3248016|taxon=''Pedum''|access-date=31 August 2022|}}</ref>

Among scallops, this species exhibits a unique lifestyle where they "bore" into live coral, creating a narrow "burrow" or niche that these scallops inhabit throughout their life. ==Description== {{Further|Scallop#Description}} {{Multiple image | image1 = Pedum spondyloideum 01.jpg | direction = vertical | caption1 = Right valve | image2 = Pedum spondyloideum 02.jpg | caption2 = Left valve | align = left }} The two shell valves of ''Pedum'' are fan-shaped and asymmetrical: the right valve has a deep byssal notch, is inflected, smoother, and is wider and larger than the left valve, which is flattened, possesses radial lines and spines.<ref name=growing/>

The scallop's mantle folds and tentacles are part of its visible anatomy; two tentacle types have been observed: a wholly white tentacle and a brown-striped variety. Like other scallops, ''Pedum'' possesses eyes.<ref name=growing/>

==Biology== ''Pedum'' occupies a unique niche among scallops; this species bores into living stony corals, burrowing into their skeleton, described as a "nestling" life habit. Phylogenetics suggests that this behavior arose from ancestors which used byssus to attach themselves to a substrate. At least one other species exhibits this life habit.<ref>{{cite journal |last1=Alejandrino |first1=Alvin |last2=Puslednik |first2=Louise |last3=Serb |first3=Jeanne M. |title=Convergent and parallel evolution in life habit of the scallops (Bivalvia: Pectinidae) |journal=BMC Evolutionary Biology |date=14 June 2011 |volume=11 |issue=164 |article-number=164 |doi=10.1186/1471-2148-11-164 |doi-access=free |pmid=21672233 |pmc=3129317 |bibcode=2011BMCEE..11..164A |url=https://link.springer.com/content/pdf/10.1186/1471-2148-11-164.pdf |access-date=24 January 2026}}</ref>

The following families were observed to host ''Pedum'' in Thailand's Andaman coast:<ref>{{cite journal |last1=Scaps |first1=Patrick |title=Associations between the Scallop Pedum spondyloideum (Bivalvia, Pteriomorphia, Pectinidae) and Hard Corals on the West Coast of Thailand |journal=Zoological Studies |date=March 2011 |volume=50 |issue=4 |url=https://www.researchgate.net/publication/282286350 |access-date=24 January 2026}}</ref> {{Div col|colwidth=24em}} * Acroporidae * Agariciidae * Faviidae * Siderastreidae * Oculinidae * Poritidae * Milleporidae {{div col end}} thumb|The rim of dead coral around this ''Pedum'' is evident Depending on the shape of its host, ''Pedum'' may embed itself obliquely (in plate-shaped corals), or deeply (in massive corals).<ref name=growing/>

To allow for the maintenance of its crevice, ''Pedum'' secretes a chemical that erodes the coral's skeleton and tissues, which has been compared to the distantly related ''Lithophaga'' mussels. Juveniles initially settle on the surface of a coral colony, slowly embedding itself and expanding its crevice; during this stage, Shell Width (SW) increases faster than Shell Height (SH). As it grows, the right valve firmly attaches to the crevice's walls, allowing the left valve to open and close. The scallop's growth keeps pace with its coral host's own growth rate. Additionally, the pallial tissues of the mantle along with the tentacles attack the coral's tissues immediately surrounding the crevice, which maintains the opening necessary for the scallop and prevents it from being entombed. This action leaves a "band" or rim surrounding the opening, which displays chemical etch marks when observed under a microscope. To retract, the scallop pulls their strand of byssus.<ref name=growing/>

These scallops may benefit their hosts by hindering their predation by the crown-of-thorns starfish (''Acanthaster spp.''), which are repelled by jets of water from the scallops (these jets are typically used to expel pseudo-feces and sediment). ''Pedum''-inhabited corals were left uneaten by the starfish, leaving a remnant region of live coral around the scallops.<ref>{{cite journal |last1=Devantier |first1=LM |last2=Endean |first2=R. |title=The scallop Pedum spondyloideum mitigates the effects of Acanthaster planci predation on the host coral Porites: host defence facilitated by exaptation? |journal=Marine Ecology Progress Series |date=August 1988 |volume=47 |issue=4 |pages=293–301 |doi=10.3354/meps047293 |bibcode=1988MEPS...47..293D |url=https://www.int-res.com/articles/meps/47/m047p293.pdf |access-date=24 January 2026}}</ref>

This species does not seem to tolerate the adverse conditions of marine lakes, where mytilid bivalves and polychaete tube worms occupy its filter-feeding niche.<ref>{{cite journal |last1=Becking |first1=Leontine E. |last2=Martinez |first2=Stephanie J. |last3=Aji |first3=Ludi Parwadani |last4=Ahmad |first4=Awaludinnoer |last5=Alzate |first5=Adriana |last6=Folkers |first6=Mainah |last7=Lestari |first7=Dea Fauzia |last8=Subhan |first8=Beginer |last9=Hoeksema |first9=Bert W. |title=Stony Corals and Their Associated Fauna Residing in Marine Lakes under Extreme Environmental Conditions |journal=Diversity |date=13 May 2024 |volume=16 |issue=5 |page=295 |doi=10.3390/d16050295 |doi-access=free |bibcode=2024Diver..16..295B |url=https://www.mdpi.com/1424-2818/16/5/295/pdf?version=1715583751 |access-date=24 January 2026|hdl=11370/1e5e1ba5-bf54-4a3f-9b3c-05edae1097a2 |hdl-access=free }}</ref>

Examination of coral growth rings containing ''Pedum'' crevices suggest that the scallops may live for at least 6 years.<ref name="growing">{{cite journal |last1=Chan |first1=Benny K. K. |last2=Tan |first2=James C. H. |last3=Ganmanee |first3=Monthon |title=Living in a growing host: growth pattern and dwelling formation of the scallop Pedum spondyloideum in massive Porites spp. corals. |journal=Marine Biology |date=4 June 2020 |volume=167 |issue=95 |article-number=95 |doi=10.1007/s00227-020-03716-8 |bibcode=2020MarBi.167...95C }}</ref>

==References== {{Reflist}}

==External links== * [http://www.repository.naturalis.nl/document/504769 Dijkstra, H. H. (2013). Pectinoidea (Bivalvia: Propeamussiidae and Pectinidae) from the Panglao region, Philippine Islands. Vita Malacologica. 10: 1-108]

Category:Pectinidae Category:Bivalves described in 1791