The Natural History Museum Fossil Porifera Collection

This article provides updated information about the Porifera Collection at The Natural History Museum (NHM), London. With very little information available regarding fossil sponge digitization or any similar initiative, this paper covers the type and figured specimens and drawer label content data of the Porifera Collection and also describes the collection and its research potential. With approximately 71,000 specimens, of which more than 60% are Mesozoic, the NHM holdings offer the best Mesozoic sponge collection in the world and one of the most important due to its breadth and depth. The Porifera Collection covers all stratigraphic periods and all taxonomic groups and includes almost 3000 cited and figured specimens including types. Although most of the specimens come from the British Isles, worldwide samples are also present, with abundant specimens from other Commonwealth countries and from Antarctica.

Minor collections, in terms of number of sponge specimens, are those of Bowerbank, which was acquired at a sale in 1865, after his retirement, and the Morris Collection which was acquired in two batches (1863,1867). There are also sponges collected by the Welsh naturalist Thomas Pennant.
Regarding their shapes and dimensions, this NHM Fossil Collection presents a great diversity, with forms such as cups, funnels, vases, cylindrical, club-shaped, fanshaped, and branching examples. One of the smallest specimens belongs to the calcareous Peronella which measures 5.5 mm in length by 4 mm in width, while the largest is a demospongea, belonging to Chenendopora, with 400 mm long and 200 mm wide.
The NHM Porifera Collection contains almost 3000 referenced individuals as hand specimens and thin sections. From these, more than 2000 are figured and the rest are cited in more than 140 bibliographic references (see Figure 1 and Appendix).
Very few specimens of this Collection have been fully digitized (less than 2%) on our NHM collection management system, but a Microsoft Excel database of 752 entries has been populated, with drawer label content that has been used to help write this article. The data recorded includes taxa, geographic site and stratigraphic locations of the specimens, with some labels also showing the donor collection. Most of the specimens have been assigned stub records in the NHM collection management system, Emu (Sendino, 2009), that are linked to images from the catalog books where the specimen registration number is recorded with taxon, geographic and stratigraphic information and acquisition details. The results shown here are based on the drawer label data concerning hand specimen and slide cabinets. In order to estimate the most accurate proportions, the specimen size has been considered. The number of specimens has been determined by counting how many specimens a drawer contains and this figure was multiplied by the entire number of drawers for each Porifera class (for hand specimen and slide cabinets). Drawers containing larger than standard-sized specimens were counted separately. Total data and percentages were estimated using Microsoft Excel. This is the first time that the drawer label content has been used to show the collection rough data and also that a complete museum fossil sponge database has been shown. This is a useful starting point for collections still not completely digitized and a good method to allow online accessibility of what museums keep in their collection. It helps with gathering taxonomic, geographic and stratigraphic data of the collection that can be used in research and curation fields such as biogeography and also highlights gaps in the collections for each group. This is a good basis for a more comprehensive database as an important source for understanding Porifera biodiversity.

Fossil Porifera Collections Elsewhere
Although  studied the British and German Palaeozoic sponges, many of those specimens kept at the NHM, there are other historically important German Palaeozoic collections which could compete with the NHM Collection. Among these are those studied by Hermann Rauff at the Göttingen Geoscience Museum and at the Naturkunde, Rudolf Kolb at the Palaeontological Museum of Munich, and Schrammen mainly at the Roemer Museum in Hildesheim and also at the American Museum of Natural History in New York. It is also important to cite the Bohemian Palaeozoic sponges studied by the zoologists and palaeontologists Antonín Jan Frič (who also published as Anton Fritsch) and Filip Počta (also published as Phillip Počta) in Bohemia.
With regards to Mesozoic sponges there is no collection that can compete with that of the NHM. Frič, Počta, Kolb and Schrammen created and described Mesozoic collections (O'Connell, 1919), and some of these were purchased by the NHM, such as the Cretaceous Porifera Collection from both Počta (1907) in 1909and Schrammen in 1920(Cleevely, 1983. Therefore, these collections are surpassed by the NHM Fossil Porifera Collection which is also cited by these authors. The NHM keeps numerous types and figured specimens that are key to taxonomic identification, including not only hand specimens, but also thin sections and cavity slides (see some of the most striking NHM fossil sponges of this Collection in Figure 2). The thin sections make the NHM Fossil Porifera Collection unique as they come from historical specimens, for which justification for destructive sampling for preparation of specimens would now be difficult, and in the specific case of the siliceous samples would be expensive to prepare as well as problematic.

Specimen Preservation Method
This NHM Collection constitutes mainly fossil specimens that are kept as hand specimens (88%) and thin sections (12%). The Recent specimens (0.2%) are preserved as dried specimens. The sponges are stored within the collection cabinets. Each cabinet holds drawers that store individual specimens from the same family, geographic location (region or country) and stratum.
There are almost 8000 thin sections, of which more than half are of stromatoporoids, and the rest are represented in the same proportions as the hand specimens. Therefore, the taxonomic representation of these thin sections in descending order is as follows: demosponges, hexactinellids, calcareous sponges and archaeocyaths. Most of these are historical specimens, prepared by Nicholson and Hinde. These thin sections are fundamental for viewing morphology and the internal microstructures required to meet criteria for taxonomic identification.

Taxonomic Coverage
The NHM Fossil Porifera Collection covers most of the Porifera groups such as demosponges, hexactinellids, calcareous sponges, archaeocyaths and stromatoporoids. The class Demospongea is the most represented in the NHM Collection, including the polyphyletic lithistid group of massive skeletons which are easily preserved in the geological record. These reached their greatest dominance during the Cretaceous. The NHM has the most important collection of Cretaceous sponges in the world, with hundreds of non-lithistid demosponges and more than 10,000 lithistids, mostly from Europe and North America. These are useful in unveiling the diverging silicification levels over time. This class is represented from the Palaeozoic to Cenozoic eras ( Figure 3) and includes almost half of the total number of the sponges in the Collection.
Hexactinellids are siliceous sponges that also range in time, as do the demosponges, from the Cambrian to Recent. They have been found living in both cold deep and warm shallow waters and have been defined as the oldest lineage of animals alive on earth today. The NHM Porifera Collection has almost a quarter of fossils of this group (Figure 3), mainly from the Mesozoic of Europe.
Calcareous sponges have skeletons with spicules of calcium carbonate and have persisted, as the previous groups, from Cambrian to Recent times, having their   (Bedford and Bedford, 1934 greatest diversification during the Cretaceous. Their Mesozoic representation stands out in the NHM Porifera Collection and represents the third biggest group of sponges. Most of them are from Europe, but there are representatives from Asia, South America and the Middle East as well. The calcareous sponges represent 10% of specimens of the entire Collection (Figure 3).
The other classes are hypercalcified sponges, the stromatoporoids and the archaeocyaths. The Stromatoporoidea, an extinct class of non-spiculate poriferans, are very well represented (Figure 3). They appeared for first time in the Middle Ordovician and became abundant and widespread through the Silurian and Devonian, until finally disappearing in the Cretaceous. The NHM Porifera Collection has more than 15,000 specimens, including thin sections, and contains the most outstanding Silurian specimens such as the historical Nicholson Collection (1886 of British stromatoporoids. Archaeocyaths characterize the first substantial diversification of the phylum Porifera, to which they are now generally assigned as a distinct class. They flourished in carbonate shelf and reef environments of the early Cambrian and a depauperate stock persisted into the late Cambrian. The Archaeocytha Collection at the NHM contains more than 700 specimens, mainly from Antarctica, Australia, Canada, Morocco, Sardinia, Siberia, Spain and USA. This is one of the most important Archaeocyatha Collections in the world, including a mixture of over 100 cavity slides and thin sections. About a hundred type and figured specimens are present among these specimens (such as in Hill (1965) and Debrenne (1969)). They represent 1% of the Collection (Figure 3).
More than 4% of the NHM Collection, 3000 individuals, have been cited and figured, including types that are key to taxonomic identification studies and should be the main goal of digitization regarding marine palaeofauna.

Stratigraphic Coverage
Stratigraphically, the NHM Fossil Porifera Collection is represented by specimens from the Cambrian to Pleistocene, but is particularly rich in Mesozoic and Palaeozoic (Figure 3) sponges. The reason for this is explained by the localities from where they were collected, a large proportion originating from the British Isles.

Geographic Coverage
Although the distribution of this Collection is worldwide, it is mainly European (80%). There is the same trend in most of the groups, with the exception of archaeocyaths. The majority of the collection is from the British Isles (61%) followed by European continental (18%). There are also abundant specimens from the Commonwealth countries (9%) and Antarctica (less than 1%).
If we study geographic origin by class, most of the demosponges are from the British Isles (62%), the European continent (25%) and in much less proportion from North America, the Arctic, Oceania, Middle East, Russia, Africa, Caribbean, Asia and South America (Figure 4). The hexactinellids are also mainly from the British Isles (66%), followed by European continental (24%) and North America, Oceania, Middle East, Russia, Africa Caribbean, and Asia.
The NHM fossil calcareous sponges follow similar proportions: British Isles (70%), European continental (12%), Asia (4%) and the other regions have similar number of specimens (North America, South America, Oceania, Middle East, Russia, Africa and Caribbean).
In the case of the stromatoporoids are also mainly from the British Isles (63%) followed, this time, by Middle East specimens (12%), Europe non-British (10%), North America (6%) and the rest from Oceania, Russia, and Africa. The archaeocyaths are mainly from Oceania (63%), Antarctica (25%) and in much less proportion from Europe, North America, Russia and Africa.

Potential Research Projects
Sponges are the oldest known metazoan group with an outstanding importance as both a living fossil and the closest related to the hypothetical ancestor of all metazoans, the Urmetazoa (Thakur and Müller, 2004). Currently their importance is also economic, being used for treating skin conditions and diseases, with, for instance, some compounds derived from Spongilla species. The three living fossil sponge classes, Hexactinellida, Demospongiae and Calcaera, are currently being used in molecular biological studies and this data could be extrapolated to fossil taxa by molecular clock technique. This Collection keeps approximately 8000 thin sections and cavity slides that will save time in preparing the specimens for taxonomic studies, as well as for climate change research and functional morphology studies. Some of the samples come from sites that are currently difficult to access, such as in the Middle East. They will also be useful in revealing the biodiversity of fossil sponges and their role as reef builders in Palaeozoic and Mesozoic times.
The study of this comprehensive collection will help to fill the gaps in our knowledge of the evolution of fossil faunas and for study of their phylogenetics. In the case of lithistids, a better understanding is needed of the diagnostic biological characters that are potentially best preserved to separate apomorphies and synapomorphies in order to distinguish subgroups and integrate them in phylogenetic studies.
Additionally, the study of the rocks associated with the specimens will disclose the paleoenvironmental conditions that favored silicification and calcification processes. These conditions are considered to be very different from those of extant taxa (Pisera, 2004), with fossil lithistids and hexactinellids with fused siliceous skeletons inhabiting shallower waters. Current fossil sponge silica research opens a door to better understanding the evolution of the group and their relevance to climate change.
Finally, new resources and tools such as 3-D reconstructions (Luo and Reitner, 2014), CT Scanning and Big Data are revolutionizing sponge biology as sponge microstructure did in Victorian times with taxonomic studies of Porifera.

Conclusion
This large NHM Porifera Collection has approximately 71,000 individuals and 4% of the collection cited and figured in bibliographical references. It is key to Porifera taxonomic identification and having historical thin sections associated with the hand specimens makes this Collection unique. This article is a first step in the digitization of this Collection and is an example of how the data populated from the drawer label content can be used to show the collection's content. The data recorded includes taxa, geographic site and strata where the specimens come from and some of the labels also named the donor collection. This is also the first time that a museum fossil sponge database has been shown.

Declaration of Conflicting Interests
The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding
The author received no financial support for the research, authorship, and/or publication of this article.