Gregory A. Lewbart
Introduction
Invertebrates are a collection of animals unified by the lack of a vertebral column. While invertebrate animals comprise greater than 95% of the animal kingdom's species well over 95% of the literature pertaining to surgery deals with vertebrates.
This chapter covers the current state of surgery on the most prominent invertebrate groups (sponges, coelenterates, mollusks, crustaceans, insects, horseshoe crabs, spiders, echinoderms, and urochordates). Since various taxa are largely unrelated and possess specialized anatomic and physiologic features, each taxon is handled separately and specific procedures reviewed and addressed accordingly.
For reviews of anesthesia and analgesia please refer to Braun et al. (2006), Dombrowski and De Voe (2007), Cooper (2011), Andrews et al. (2013), Gunkel and Lewbart (2008), Mosley and Lewbart (2014), Fregin and Bickmeyer (2016), Butler‐Struben et al. (2018), and Archibald et al. (2019).
Porifera (Sponges)
The phylum Porifera is a diverse group of primitive animals commonly referred to as sponges. Until the early 1800s, sponges were actually classified as plants. Sponges occur in fossil records back to the Precambrian Era (over 600 million years ago) and were the most important contributors to reefs during the Palaeozoic and Mesozoic Eras (Hooper and Van Soest 2002). All members lack defined organs; however, differentiated cells within connective tissue perform necessary biologic functions. Unique systems of water canals facilitate transport of food, waste products, and gametes. Most of the 5000‐plus species are marine with just 3% of sponges occurring in freshwater environments. Sponges are normally found on firm substrates in shallow water, although some occur on soft bottoms.
Sponges maintain a close association with a variety of bacterial genera. While some can be pathogenic, most form a symbiotic relationship with the sponge and provide nutrients. These symbionts are what impart the vast array of bright colors seen in some sponges.
Surgery on sponges is frequently employed to study regeneration and reproductive strategies (Korotkova 1970; Simpson 1984; Kuhns et al. 1997; Henry and Hart 2005). A recent study by Borisenko et al. (2015) examined regeneration in the sponge Halisarca dujardini (Figures 4.1 and 4.2). The authors were interested in healing at the cellular level and use microscopy to describe the production of a blastema, an accumulation of undifferentiated cells that will become a new tissue or organ (Carlson 2007). In the case of sponges, the blastema differentiates into new sponge tissue capable of nearly all biologic functions. In the Borisenko et al. (2015) study, the authors used Castroviejo scissors and microscalpels to perform the tissue excisions under a stereomicroscope.
Coelenterates
This large taxonomic grouping includes two phyla: the Ctenophora (comb jellies) and the Cnidaria (Hydrozoans [hydras, fire coral, Portuguese Man‐O‐War], Scyphozoans [jellyfishes], and Anthozoans [stony corals, soft corals, sea anemones]). This is an economically important group for research, environmental monitoring, public and private display, tourism, and to a lesser degree human food. Coral reefs collectively are one of the most beautiful, diverse, economically important, and fragile ecosystems on the planet. The most common surgery performed on coelenterates involves fracturing pieces of hard coral or cutting segments of soft coral for propagation. This surgical process is referred to as “fragging” in the hobby industry. The technique requires some creativity and foresight, but the procedures are easy to master. For hard coral fragging, remove large “parent” corals from a system and fracture off small sections with a suitable instrument (e.g. rongeurs, bone cutters) and then secure carefully to a pedestal or other firm substrate with waterproof adhesive. Figure 4.3 shows a system full of “frags.” For soft corals, use sharp scissors to sever a suitable fragment that can be attached to a substrate with monofilament suture.
Figure 4.1 This schematic shows the cellular structure of a sponge (Halisarca dujardini). The dotted line represents an area of surgical excision.
Source: Borisenko et al. (2015).
Figure 4.2 This schematic shows three stages of regeneration in the sponge, Halisarca dujardini. (a) Normal sponge. (b) Formation of a “regenerative plug” (Stage I). (c) Formation of a “blastema” (Stage II). (d) Ectosome and choanosome restoration (Stage III). Cell colors correspond to Figure 4.1.
Source: Borisenko et al. (2015).
Another process that is occasionally utilized with corals is transplantation. Much work has gone into the process with many species belonging to both invertebrate and vertebrate taxa. With coelenterates, autogenous grafts generally take well, but allografts and xenografts do not (Bigger and Hildemann 1982). In the case of corals, polyps from the same colony can be surgically removed and then attached to another area of the colony with good success as long as freshly cut polyps are placed adjacent to one another (Hildemann et al. 1974).
Coelenterates have an amazing ability to heal and regenerate. This has been know and studied for well over a century (Metchnikoff 1892; Bigger and Hildemann 1982). Amebocytes play an important role in the healing process and it appears that specialized “wound cells” are involved in the initial reaction and healing process, at least in anemones (Young 1974).
Figure 4.3 This aquarium is filled with coral “frags” representing a number of species and morphological types.
One can purchase commercial fragging kits from companies such as Tamsco (Bridgeview, IL), TB Aquatics (Flemington, NJ), and DR Instruments (Palos Hills, IL). Numerous demonstration videos can be found on “YouTube” that illustrate the process of fragging corals.
Gastropod Mollusks
The gastropods belong in the phylum Mollusca and include over 60,000 marine, fresh water, and terrestrial species. The group includes abalone, conchs, nudibranchs, sea hares, slipper shells, slugs, snails, and whelks, among many others. They account for approximately 80% of all mollusk species. Gastropods have a ventrally flattened foot that provides locomotion along the various surfaces of their habitats. They are important display, food, and research animals. Some species are successfully cultured although wild capture is the most common method of procurement. They can be quite large and many are long‐lived. Investigators working on the sea hare, Aplysia, were awarded a Nobel Prize for medicine or physiology in 2000 for their work on neurophysiology, behavior, and learning. The Nobel Prize in Physiology or Medicine 2000. NobelPrize.org. Nobel
