et al. (2014) determined that polyglactin 910, among the five suture materials (braided silk, chromic gut, monofilament nylon, polydioxanone, and polyglactin 910) tested in the skin of Lumbricus terrestris, resulted in the most tissue holding security. Moderate tissue reaction was noted to all five suture materials. A study from the human medical literature focused on anchoring the medicinal leech (Hirudo medicinalis) to patients with superficial and deep tissue with braided silk found found no difference in survival among leech groups with deep and superficial braided silk versus control leeches without suture (Davila et al. 2009).
Crustaceans
The crustaceans are a highly successful class of the Phylum Arthropoda although the nomenclature ranking varies among scientists. This group includes lobsters, crabs, crayfish, shrimp, barnacles, and hermit crabs. Numerous other taxa belonging to this taxon include isopods, amphipods, and brine shrimp. Economically, this is one of the most important groups of invertebrates and its members are utilized for food, as display animals, and for research.
Like many of the preceding taxa, much of the surgery applied to crustaceans has been in research and not the clinical setting. Scientists implant electrodes to study physiology (Forgan et al. 2014), surgically remove eyestalks to impact reproductive behavior (Uawisetwathana et al. 2011), sever nerves to study blood pressure changes (Wilkens and Young 2006), ablate neurons to study regeneration of these structures (Harrison et al. 2003, 2004), and use fine forceps to remove the gonads of a pill bug‐like isopod (Suzuki and Yamasaki 1991).
In a more ambitious technical work, Weissburg et al. (2001) transplanted fiddler crab (Uca pugilator) limbs in order to study the well‐known differences between male and female behavior in this species and the neurosensory basis of these behaviors. Fiddler crabs will autotomize limbs when stressed or traumatized. The researchers would apply pressure to a portion (merus) of the feeding appendages in order to induce autotomy. The animals were then maintained through molting stages until a 2.0 mm limb bud appeared. At this time, the animals were placed in 25 ppt artificial seawater with 30 mg/L gentamicin and 4.0 ml/L Fungizone® for three days before surgery. Host crabs were similarly prepared and another surgeon‐induced autotomy of the major claw, and a donor bud was secured to the empty socket with cyanoacrylate adhesive. Over a three‐year period the authors transplanted over 680 claws with 101 developing into functioning feeding claws by the second postsurgical molt. For a thorough review of autotomy among the invertebrates, please refer to Fleming et al. (2007).
Arachnids
The Class Arachnida is a huge group of animals (over 100,000 species) that includes over 30,000 spiders, and less conspicuous groups such as the harvestmen, mites, ticks, and scorpions. Tarantulas (actually not true spiders) represent an important taxon of commonly kept arachnids that commonly require medical care. Scorpions also appear with some frequency in the pet trade and are common display animals in zoos and museums.
Surgical repair of the fractured exoskeleton can be accomplished with surgical adhesives like methylmethacrylate or cyanoacrylate (Wolff 1993). A fractured abdomen in a tarantula carries a grave prognosis, but if the hemolymph hemorrhage can be contained with the use of a topical adhesive, the animal can survive. Another common problem that may require intervention is dysecdysis (difficulty shedding). A tarantula or other arachnid that experiences this life‐threatening problem can be either anesthetized or manually restrained while forceps or other appropriate instruments are used to gently extract the animal from the adhered exoskeleton (Figure 4.8).
Like many arthropods, scorpions can display autotomy (Pizzi 2002), but in the case of some species belonging to the genus Ananteris, they can autotomize their tail (metastoma), including a portion of the gastrointestinal (GI) tract, and survive for up to eight months (Mattoni et al. 2015). Virtually all other arthropods that practice autotomy drop (and can redevelop) limbs. In the case of the Ananteris scorpions, tail autotomy appears to be a defense or escape response practiced most commonly by males. While survivors can no longer defecate or sting, they can live long enough to consume small meals and mate (Mattoni et al. 2015). According to one study, sutures are of little use on spiders (Pizzi and Ezendam 2002). Autotomy can be induced in tarantulas by using forceps to grasp the injured appendage by the most proximal segment (femur) and quickly pulling upward (Zachariah and Mitchell 2008). Another small surgical procedure involves inserting microchips (passive integrated transponder [PIT] tags) into manually restrained tarantulas. To do this, an area on the opisthosoma between the heart and intestines was prepared by gently removing the setae from a 1.5 × 1.5 mm area with a 20‐gauge needle. The needle tip was then used like a scalpel to open the exoskeleton allowing for insertion of the PIT tag with fine sterile forceps. The wound was then dabbed dry and sealed with cyanoacrylate to minimize hemolymph loss (Reichling and Tabaka 2001).
Figure 4.8 This image shows the careful removal of a retained exoskeleton from a tarantula.
Source: Courtesy of Dan Johnson.
Limulus
Limulus polyphemus, the American horseshoe crab, is actually not a crab at all but a member of the Class Merostomata in the Phylum Chelicerata. Horseshoe crabs are more closely related to arachnids than crustaceans. Limulus is a very important animal for biomedical research, is used as bait and fertilizer, and is an important display and “touch tank” animal in public aquaria (Smith and Berkson 2005; Smith 2012). The anatomy and physiology of these animals have been thoroughly researched, and they are easy to handle and work with. Investigators examining vision and communication of the numerous ommatidia in the Limulus lateral eye were awarded the Nobel Prize for medicine or physiology in 1967 (Hartline and Ratliff 1958).
Trauma to the exoskeleton can be stabilized using epoxy. In the case of a fractured carapace, prepare the exoskeletal area where the epoxy will be affixed with an abrasive material like sandpaper. Manually reduce the fracture and stabilize it with the epoxy using digital pressure (Figure 4.9). The epoxy braces can be left in place as long as needed, but healing should occur within three to four months (Smith 2012).
Figure 4.9 These images illustrate fracture repair of a horseshoe crab (Limulus polyphemus) prosoma caused by a fall from a raised, shallow tank. (a) The fracture is located on the animal's right side and extends from an area rostral and medial to the compound eye caudally through the arthrodial ligament. (b) A sandpaper wheel is used to freshen areas of the prosoma for better epoxy adherence. (c) The fracture was manually reduced and stabilized, while a suite of four epoxy bridges were placed. (d) The animal responded well to the procedure and can be seen in its tank several weeks later.
Healing is initiated by amoebocytes, which initially form a clot, and progresses to scab formation and tissue
