Dogfish Dissection Part 1 PDF

SPINY DOGFISH SHARK DISSECTION: PART 1 Squalus acanthias BIO 415L Presented by Dr. Sarah Polekoff DOGFISH STRUCTURES Skeletal elements: External Structures: Muscular System (Cutting Line 1): Chondrocranium Naris...

SPINY DOGFISH SHARK DISSECTION: PART 1 Squalus acanthias BIO 415L Presented by Dr. Sarah Polekoff DOGFISH STRUCTURES Skeletal elements: External Structures: Muscular System (Cutting Line 1): Chondrocranium Naris Spiracle Splanchnocranium Eye Meckel’s cartilage Vertebral column Mouth Adductor mandibulae m. Rib Labial pocket External pharyngeal slit Pectoral girdle Spiracular valve Scapular process Pectoral fin Spiracle Myomere Pelvic girdle External pharyngeal slits Myoseptum Pelvic fin Interbranchial septum Epaxial musculature Anterior dorsal fin Lateral line Horizontal skeletogenous septum Posterior dorsal fin Fin spines Hypaxial musculature Caudal fin Anterior dorsal fin Linea alba Posterior dorsal fin Pectoral adductor m. Caudal fin Ampullae of Lorenzini Pelvic fin Pectoral fin Clasper (male) Cloaca Abdominal pore Urinary papilla (male) Urogenital papilla (females) Tetrapod Evolution Types of “fishes” Cartilaginous fish Ray-finned fish Lobe-finned fish Tetrapod Evolution  Epaulette shark walking:  https://youtu.be/tRDwzQ3gz8Q  https://youtu.be/ndbw7SQMCcQ Dogfish Background https://www.youtube.com/watch?v=XBicohkA2eE  SPINY DOGFISH SHARK—Squalus acanthias  Chondrichthyes (includes sharks, skates, rays, sawfishes, and holocephalimorphans)  Cartilaginous skeleton  Perichondral and endochondral mineralization  Row of serrated, triangular, and pointed teeth:  Line the upper and lower jaws and are followed by rows of teeth that can rapidly replace those that become broken or worn. Dogfish Background  Distinctive placoid scales (‘denticles’)  Pelvic claspers in males  Fusiform bodies with well-developed paired fins  Five to seven pharyngeal slits and usually a spiracle (posterior to eye)  Spiracles act like a straw or snorkel, drawing water over their gills and out the gill slits.  Lack the swim bladder or lung:  Large oil-filled liver reduces their specific density.  SKELETAL ELEMENTS https://youtu.be/PTdL0Z qkQEQ  Head includes the chondrocranium and splanchnocranium.  “Splanchno” refers to the “viscera”  Vertebral column: from chondrocranium >>> tail.  Supports the anterior dorsal fin, posterior dorsal fin, and caudal fin.  Pectoral girdle, supporting the pectoral fins, lies just posterior to the splanchnocranium  Pelvic girdle, supporting the pelvic fins, lies farther posteriorly  NOTE: Pectoral and pelvic girdles are isolated components without direct attachment to the rest of the skeleton.  Dorsal Ventral CHONDROCRAMIUM  Rostrum: scoop-like.  Contains the precerebral cavity.  Rostral carina:  Supports rostrum ventrally  Nasal capsules (paired)  Lateral to the base of the rostrum  Nares (paired):  May be preserved on the surface of each capsule.  Orbit:  Occupied by the eyeball  Optic pedicle:  Supports the eyeball  Otic region:  Behind the orbits. Contains the otic capsules that house the inner ears.  Occipital condyle:  Joint with vertebral column FORAMENS (FYI)  Carotid foramen  Endolymphatic foramina and perilymphatic foramina  Superficial ophthalmic foramina, pierce each supraorbital crest.  Optic foramen: anteroventrally in the orbit.  Trigeminofacial foramen  Eyes: trochlear, abducens, and oculomotor foramina  Hyomandibular foramen  Foramen magnum:  Large median opening for spinal cord  Vagus foramen  Glossopharyngeal foramen lies at each ventrolateral corner of the occipital region. SPLANCHNOCRANIUM: Head and Viscera 7 visceral arches: 1. The mandibular arch 2. Hyoid arch 3. 5 branchial arches Mandibular and hyoid arches: Highly modified for their use as jaw elements and jaw supports. Branchial arches Support the interbranchial septa Mandibular arch The largest of the arches Forms the jaws.  Palatoquadrate cartilages (paired): SPLANCHNOCRANIUM Form upper jaw https://youtu.be/ Orbital process eh_HUIJkRzU Contacts the medial wall of the orbit. Adductor mandibulae process: Attachment of the jaw-closing musculature Lower jaw: Ventral half of the mandibular arch and paired Meckel’s cartilages fused anteriorly Labial cartilage: Support labial fold. Hyoid arch Modified to support the jaws (or mandibular arch).  VERTEBRAL COLUMN  2 vertebral types, 1. Trunk vertebrae 2. Caudal vertebrae.  Notochord: Compare with arcualia of lamprey (image above)  Within the centrum in a sagittal section: axial support  Basapophysis:  Projects on either side from the ventrolateral surfaces of the centra of the trunk vertebrae.  Ribs articulate here “The notochord is a rod-like embryological structure, which plays a vital role in the development of the vertebrate. Though embryological, remnants of this structure have been observed in the nucleus pulposus of the intervertebral discs of normal adults” (Ramesh et al., 2017)  SKELETAL ELEMENTS (Cont’d)  RIBS:  Projects from the basapophysis.  FINS  ANTERIOR DORSAL FIN & POSTERIOR DORSAL FIN: 1. Basal pterygiophore: fin spine is anchored anteriorly. 2. Radial pterygiophores (series of projections): distal 3. Ceratotrichia, which are FIBROUS dermal rays >>> NOT cartilaginous elements.  CAUDAL FIN: asymmetric  Vertebral axis curving into the dorsal lobe of the fin  Supported proximally by the hemal arches and radial pterygiophores. PECTORAL GIRDLE  Scapular process:  Coracoid bar + dorsal extension past the attachment of each fin.  Suprascapular cartilage: separate slender element attaches dorsally to each scapular process.  Glenoid surface: area that articulates with the fin at mesopterygium  Pectoral fin: Basal pterygiophores > radial pterygiophore > ceratotrichia  3 basals: propterygium, mesopterygium, and metapterygium  Radials: rod-like structures, more regularly shaped than in the median dorsal fins  Arranged in rows. PELVIC GIRDLE  Pelvic girdle is composed of a single element: the puboisciadic bar  Pelvic fin:  MALE: differs in bearing a clasper, formed from modified radials.  Bring sperm into the cloaca of the female.  Clasper: hook and spine distally  FEMALE: the pelvic fin of the female and male are similar with short propterygium and a stout, elongated metapterygium that extends posteriorly. EXTERNAL STRUCTURES  Non-keratinized dermis and epidermis  Thin skin!  Covered in mucus  Observe under the microscope:  Placoid scales or denticles are embedded in the skin.  Built like a tooth: 1. Formed from dentine 2. Covered by enamel 3. Containing a pulp cavity  Reduce the drag of water passing over the skin  Melanophores:  Within integument  Specialized cells: control pigmentation of the skin and secretory cells  Cannot be seen grossly. EXTERNAL STRUCTURES  Spine of scale (c.s.)  Enamel (c.s.)  Dentine (c.s.)  Pulp cavity (c.s.)  Epidermis (c.s.)  Dermis (c.s.) Melanophores seen on microscopy in lab EXTERNAL STRUCTURES (Cont’d)  NARIS: nares (sing. naris).  Ventrolaterally on the tapered snout.  Incompletely subdivided by a flap of skin into incurrent and excurrent apertures.  The naris leads into the blind-ended olfactory sac  MOUTH and LABIAL POCKET: supported by upper and lower jaws.  Rows of sharp teeth.  A labial pocket on either side of mouth.  Labial fold (flap): separate mouth and pocket are separated by a flap. Supported by the labial cartilage. EXTERNAL STRUCTURES  EYE: 2 groups of extrinsic eye muscles (Oblique and Rectus M. to be discussed later) 1. Dorsal oblique muscle 2. Ventral oblique muscle 3. Lateral rectus muscle 4. Medial rectus muscle 5. Dorsal rectus muscle 6. Ventral rectus muscle EXTERNAL STRUCTURES (Cont’d) https://youtu.be/8bRIuf6EtsA https://youtu.be/8bRI  EXTERNAL PHARYNGEAL SLITS: part of head uf6EtsA  SPIRACLE and SPIRACULAR VALVE:  Relatively large opening into the pharynx  Spiracular valve or Anterior fold of tissue:  Can be folded over the opening to close the spiracle.  Posterior to each eye  The valve bears a pseudobranch, a reduced gill, on its posterior surface.  External pharyngeal slits (5 total) separated by 4 interbranchial septa EXTERNAL STRUCTURES (Cont’d)  INTERBRANCHIAL SEPTUM:  Pharyngeal slits leads into the pharynx.  Water leaves the pharynx as the water passes over the respiratory structures or gills.  Gills are made up of gill lamellae (injected with red latex)  Lamellae: present on the anterior wall of the first slit, but NOT on the posterior wall of the last slit. EXTERNAL STRUCTURES (Cont’d) https://www.youtube.com/w  LATERAL LINE and LATERAL LINE SYSTEM/CANAL atch?v=9S8a5hSc22s  Faint, pale lateral line extending anteroposteriorly.  Marks the position of the lateral line canal  Cutaneous tube that contains sensory nerve endings and opens to the surface by way of tiny pores  Sensory cells responsive to pressure changes caused by vibrations and movements in the water. EXTERNAL STRUCTURES (Cont’d)  LATERAL LINE (Cont’d)  Balancing apparatus is contained within the otic capsule of the chondrocranium.  Connected to the surface by a pair of endolymphatic ducts (recall the endolymphatic foramina)  Open through the endolymphatic pores.  These lie dorsally on the head between the spiracles.  EXTERNAL STRUCTURES  LATERAL LINE (Cont’d)  The second modification consists of the ampullae of Lorenzini  Function in electroreception.  The ampullae open in numerous pores all around the head  May be noted by gently squeezing these regions to extrude a gel-like substance. be.com/watch?v=JDPFR6n8tAQ https://www.youtube.com/wat ch?v=JDPFR6n8tAQ EXTERNAL STRUCTURES (Cont’d)  FINS: lateral undulations of the tail and caudal fin produce the propulsive force that moves the shark forward.  Fin spines:  Gives rise to common name, spiny dogfish. Spines on the anterior and posterior dorsal fins.  Anterior dorsal fin and posterior dorsal fin (singles)  CAUDAL FIN (tail)  PELVIC FIN and PECTORAL FIN (paired) EXTERNAL STRUCTURES (Cont’d)  Clasper (male):  Elongated, cylindrical, and dorsally grooved  Copulatory organ  Posterior extension of the medial aspect of the pelvic fin  Cloaca:  Chamber into which the urinary, reproductive, and digestive tracts exit.  Abdominal pores:  One each on the posterolateral side of the cloaca.  Extend into the pleuroperitoneal cavity  May allow removal of excess fluid from the cavity. EXTERNAL STRUCTURES (Cont’d)  Urogenital papilla (male):  Opening of genital and urinary ducts  Cone-like structure lying in the cloaca.  Paired sperm sacs at the posterior ends of the seminal vesicles receive the seminal secretions.  Urinary papilla (females):  Only the urinary ducts open at its tip Dissection Preparation MUSCULAR SYSTEM (to be discussed) References Iuliis, G. D., & Pulerà, D. (2019). The Dissection of Vertebrates (3rd Edition). Elsevier S & T. https://bookshelf.vitalsource.com/bo oks/9780124105003 Ramesh, T., Nagula, S. V., Tardieu, G. G., Saker, E., Shoja, M., Loukas, M., Oskouian, R. J., & Tubbs, R. S. (2017). Update on the Notochord Including its Embryology, Molecular Development, and Pathology: A Primer for the Clinician. Cureus, 9(4), e1137. https://doi.org/10.7759/cureus.1137