Shellfish Lab Report

Introduction

In this laboratory report, I will be comparing examples of species from two families of molluscs, bivalves and gastropods. The six species I am reporting on are divided in half by family. The three bivalve species, classified within the family Veneridae, are Austrovenus stutchburyi, Ruditapes largillierti, and Bassina yatei. The three gastropod species I have chosen to report on, Astraea heliotropium, Turbo smaragdus, and Cookia sulcata, are in the family Turbinidae. The purpose of this is to record and report the distinctions of these species, where they lived around coastal New Zealand, and how each would have impacted the archaeological record.  This report will also aid in the identification of distinctive characteristics of various species to more easily distinguish them within an archaeological or fossil record.

Bivalvia

Species 1 – Austrovenus stutchburyi 

Figure 1. Overhead view of the exterior valve of Austrovenus stutchburyi.

Figure 2. View of the interior valve of Austrovenus stutchburyi.

Figures one and two identify parts of the species Austrovenus stutchburyi or the Tuangi Cockle or the Little Neck Clam. This cockle’s shell exterior displays a checkered growth pattern with thicker visible costae rings running parallel to the growth rings, from the umbo at the dorsal margin to the opening at the ventral margin, as shown in Figure 1. In Figure 2 the interior of the shell is visible where we can see the concave angle moving into the muscle scars and the thinner pallial sinus while moving toward the ventral margin. On the edge of the shell’s ventral margin, the lines of the ribs can be seen across the Cockle Shells’ opening. From the interior view (Figure 2) the umbo can be seen protruding from the exterior side and the inside shows the two lateral and the one cardinal teeth, which would’ve held the shell’s two valves together along with the ligament. They have thicker shells, but individuals’ characteristics are extremely variable in thickness, size, shape, height, and interior depth though in general, the cockle’s shape is “subcircular, weakly trigonal or elongated-oval” (Beu & Raine, 2009). The two muscle scars are located close to the dorsal margin on opposite sizes with the posterior scar appearing wider than the anterior scar.

The Tuangi Cockle is most commonly found on the tops and bottoms of both the North and South Islands of New Zealand along with Stewart Island, the Chatham Islands, and the islands of the sub-Antarctic. Cockles bury themselves inside the mud of estuaries and brackish streams, between the depths of 30mm and 50mm due to their filter-feeding strategy (Beu & Rain, 2009, Powell, 1979: 426). Cockles are edible and are farmed even today, which could be a holdover or influence from the Māori pre-contant period diet (MarineLife, 2019, Powell, 2009).

Species 2 – Ruditapes largillierti

Figure 3. Overhead view of the exterior valve of Ruditapes largillierti (https://animalia.bio/ruditapes-largillierti).

The Ruditapes largillierti or Oblong Venus shell has an oval shape with a shallower concavity until reaching the far dorsal end moving toward the umbo. The umbo, shown in Figures 1 and 2, is thick and the example drawn protrudes slightly less than other species within the family Veneridae. On the exterior, in Figure 1, the growth lines can be seen as extremely close together and shallow making the texture smooth. In Figure 2 the variation in depth is described by the shadowing, including the depth of the gaps between the cardinal and lateral teeth. The ligament is short and the escutcheon thin. The muscle scars shape deeper into the shell, with the posterior scar being larger and more teardrop-shaped than the scar on the anterior side. The shape of the posterior muscle scar is influenced by the large pallial sinus, which moves into the ventral edges’ flatter and longer pallial line.

Figure 4. View of an interior valve of Ruditapes largillierti (https://animalia.bio/ruditapes-largillierti).

Like the Tuangi Cockle, the Oblong Venus Shell has a distribution around both the islands of New Zealand, Stewart Island, the Chatham, and the sub-Antarctic Islands (Powell, 1979: 426). It is an endemic species that filters its food while buried in sandy or muddy bottoms in the intertidal area of the semi-protected shores of harbors, estuaries, and channels (MarineLife, 2019). According to the research done by the University of Otago, the edibility of the species is unknown, however, if one looks at the Māori name for the species, Hākari, which also means ‘to feast’, ‘to dress or adorn the hair’ as a verb and also the nouns of a banquet and a gift (Māori dictionary). While I wasn’t able to find solid evidence of the use of the shell in these different aspects of Māori society, the use of language is a hint into the past of the pre-contact culture.

Species 3 – Bassina yatei

Figure 5. Overhead view of the exterior right valve of Bassina yatei (Photo Credit: Rod Morris, available from www.rodmorris.co.nz).

Figure 6. View of the interior valve of Bassina yatei.

The Bassina yatei or Frilled Venus Shell is named for and most easily distinguished from other species by the frilled growths on its growth lines, as seen in Figure 5. The interior view of the shell in Figure 6 shows the long ligament through the thicker escutcheon and the large gaps between the lateral and cardinal teeth. In the example that is shown in this report, the posterior muscle scar is definitively smaller and less deep than the anterior muscle scar, an attribute exclusive to this species within this report. The pallial sinus has similar dimensions to the anterior muscle scar (Figure 6), which creates a flatter pallial line moving from the base of the pallial sinus to the base of the anterior muscle scar. Like the Tuagi Cockle the Frilled Venus Shell also has vertically running scars along the ventral margin (Figure 6), which help to distinguish those two species from the family Veneridae.

The distribution covers both major New Zealand Island, but examples haven’t been found on a perimeter pattern around them, staying more localized in the Northland and Auckland harbors, off of Timaru on the South Island, and the northern side of Stewart Island (Matsukuma, 1988: 570 & Powell, 1979: 427). They live in the sandy bottoms in intertidal zones between the depths of 6 to 9mm. According to a study done by the New Zealand government fishery Frilled Venus Shell are not normally fished commercially and are classified as by-catch. In Māori tradition, these shells were only collected when they washed up on shore because only scattered remains have been found within a few middens (Fisheries New Zealand, 2019: 258-259).

Comparison

The distinctions of the shells are readily apparent from their exteriors. In Figure 1 the Tuangi Cockle has a checkered line pattern unlike either the Oblong Venus Shell (Figure 3) or the Frilled Venus Shell (Figure 5). The Oblong Venus Shell has a wider shell than the other two, with a slight right angle due to the longer ligament and thinner escutcheon extending to the posterior margin (Figure 4) and the Tuangi Cockle specimen had the roundest overall shape (Figure 1). The frilled Venus shell has uplifted ridges along the growth rings, as shown in Figure 5, while the Oblong Venus Shell has flattened growth rings (Figure 3). Of the valve specimens drawn the Oblong Venus shell has the shallowest depth of concavity, followed by the almost equal depth of the Tuangi Cockle and Frilled Venus Shell. Another main distinction between the three species is the indentations caused by the pallial sinus and muscle scars. The species that is most distinctive between the three examples is the Tuangi Cockle. Figure 2 shows that there is a larger gap between the posterior side’s upper muscle scar and the much thinner pallial sinus. And between the Oblong Venus Shell and the Frilled Venus Shell in Figures 4 and 6 respectively the Oblong Venus Shell has wider and more rounded muscle scars on the posterior side than the Frilled Venus Shell, which has shallower and more oval-shaped muscle scars. The larger size of the anterior muscle scar in the Frilled Venus Shell (Figure 6) is an indicator of a larger foot while the posterior indentations indicate the size of the inhalant (pallial sinus) and exhalant (posterior muscle scar) siphons (Helm, 2004: 20-22).

All of these examples from the Veneridae family are found along the coasts of the North, South, and Stewart Islands, while both the Tuangi Cockle and Oblong Venus have distributions extending to the Chatham Islands and other sub-Antarctic Islands to the South of New Zealand (Powell, 1979: 426-427). Two of these species, the Tuangi Cockle and the Frilled Venus Shell are both still farmed and edible while the Oblong Venus Shell is edible, but has been limited in commercial farming because it lives in deeper sediment (Bue & Raine, 2009 & Cook, 2009). Because of the continuous farming, the average size of each, and where on the muddy shore the species can be found we can read that the species would have a higher possibility of being a pre-contact food source (Bue &Raine, 2009 & MarineLife, 2019).

Gastropoda

Species 1 – Astraea heliotropium 

Figure 7. Typical, top, and posterior views of the external features of Astraea heliotropium and the operculum (uk.inaturalist.org).

Distinct for the growths along the sutures (Figure 7) the Astraea heliotropium or Circular Saw Shell grows its whorls in a mainly horizontal direction from its apex leading to a short spire, flattened anterior base, wider inner lip and an oval-shaped aperture and operculum (Figure 7). The sawtooth-shaped growths align with the varices and ribs. Because of the natural growth angle of the pyramidal-shaped shell (Figure 7), there is a slight shoulder visible near a top whorl, not always present within the species in this report. The outer lip protrudes more than the other species in this report and there could be an anterior notch in the side of the aperture. In addition, because of the growth patterns, this species was the largest examined.

Can be found surrounding all New Zealand Islands and the Chatham Islands grazing along the sub-tidal rocky reef bottom (Powell, 1979: 66 & Cook, 2009). Because proper resources could not be found, for this report it is unknown if this species is edible, research pointed toward information that today the species is collected for its shell (Cook, 2009). 

Species 2 – Turbo smaragdus 

Figure 8. Typical and Posterior views of the external features of Turbo smaragdus (uk.inaturalist.org).

Figure 9 & 10 – Lateral and posterior views of the operculum of Turbo smaragdus (uk.inaturalist.org).

This coin-sized species, Turbo smaragdus or Lunella smaragdus also known as the Cat’s Eye, has a more tightly coiled appearance than the other species described in this report, which leads to the anterior base being more rounded (Figure 8). The small apex and quickly growing dimensions of the aperture grow out from the small spire (Figure 8). The whorls on this species extend from deep sutures and grow into the round aperture (Figure 8), which affects the shape of the operculum (Figure 9 & 10). The operculum is a rounded dome shape with the growth looping straight from the middle (Figure 10). Figure 8 shows the growth lines are close together and wavy on the way around the whorls causing a rough, wavy, and thin outer lip. The shoulder on the Cat’s Eye is not well defined because of the rounded form (Figure 8).

Growing in abundance in the rocky shore intertidal area on New Zealand’s North, South and Stewart Islands the Cat’s Eye can be seen during mid and low tide. The pre-contact Māori called them pūpū, found them to be edible, and had them included in a traditional tale (Cook, 2009 & Wassilieff, 2006). 

Two brothers had to stay the night with their evil grandmother, who ate members of her family. Afraid that she would eat them the boys found the operculum of the Cat’s Eye and placed them over their eyes at night, tricking her into thinking the boys were awake so she didn’t eat them (Wassilieff, 2006).

Species 3 – Cookia sulcata

Figure 11. Typical, top, and posterior view of the external features of Cookia sulcata (www.conchology.be).

Figure 12. Views of the operculum of Cookia sulcata (uk.inaturalist.org).

The Cookia sulcata or Cook’s Turban is described as ‘hand-sized’ with a shell length between 50 mm and 90 mm (Cook, 2009 & Powell, 1979: 67). The large, thin shell is cone shaped with the anterior base outline being rounded, but the aperture has an overall oval shape, leading to the same perimeter shape in the operculum (Figure 11 & 12). The spire is slightly elevated, with the roughly same size as the body whorl (Figure 11). The sutures are deeply impressed which separates the well-rounded whorls and their wavy growth lines, which create the varices (Figure 11). The base is flattened with concentric densely packed growth lines creating a deeply concave and indented in the place of the umbilicus. The aperture is transversely oval, very oblique, pearly and somewhat corrugated within. The thin columella is bow-shaped. The umbilical region and part of the base are covered with a thin callus (Figure 11) (Powell, 1979: 67). The operculum’s anterior side (Figure 12) has a concave shape and on the posterior, the growth lines extend from the corner, rather than the center.

The Cook’s Turban is another species that is endemic to both islands of New Zealand, along with the Stewart and Chatham Islands, found in the rocky reef and rocky shore sub-tidal zone (Powell, 1979: 67 & Cook, 2009). The Māori called them Toitoi, found that they are edible, and are common parts of some coastal Māori diets (Cook, 2009).

Comparison

If the operculum is part of the midden materials the family can be easily distinguished because of their existence along with their rounded or oval shape, absence of spines, and pattern of growth on the flat base (Figures 11 & 14]. Distinctions between the shells are evident in the figures above. The shape of the aperture or opening influences the shape of the operculum by the base of the shell. The Circular Saw Shell’s aperture has a wider, oval shape, distinct from the Cat’s Eye shell which has a rounded dome shape. The example species in the Turbinidae family that appear in this report have flatter bases due to the shorter columella, which itself is not visible, and the more horizontal or outward growth of the whorls (Figures 7, 9, & 12) from the apex and protoconch. These species’ bases don’t appear to have the thin anterior notch or the thin siphonal canal that other gastropod families will. The differences between the species above are the height of the spires above the body whorl (Figures 7, 9, & 12). The sutures of the Circular Saw were more defined in the shell, followed by the depth of the sutures of the Cat’s Eye, and the least defined sutures of the Cook’s Turban Shell. The most obvious difference in sutures is from the Circular Saw Shell and the saw-like ‘teeth’ from which it gets the name (Figures 7 & 8) while the other two example species are smooth. The form of the growth rings and the presence or absence (in Cat’s Eye) of ribs and varices are also distinctive of which species one is looking at (Figures 7, 8, 9, 10, 12, & 13). 

The members of the Gastropod family Turbinidae have highly calcified opercula as a means of passive defence to keep predators from taking the meat out through the shell’s aperture with the thicker shells being created closer to the warm equatorial waters (Vermeji, 2007: 67-69). This leads to most predators, including humans, breaking through the whorls of the shell to pull the meat out from the inside (Vermeji. 2007: 67-68). All three examples in this family live in either the rocky reef, sub-tidal zone [Cooks Turban and Circular Saw Shell] or the rocky shore, intertidal zone [Cook’s Turban and Cat’s Eye] (Cook, 2009). Each species can, thus survive in semi-exposed to exposed tide areas. 

Due to the necessary calcification of the thick operculum, the family can survive and grow better in warmer waters (Vermeji, 2007). The family Turbinidae, therefore, has distribution all around New Zealand and reaches the Chatham Islands, but its habitat does not move south past the northern side of Stewart Island (Powell, 1979: 66). With the wide range of distribution area that is covered, the general range of the nearby, semi-exposed shoreline habitat, and the continuous edibility of species several species in the family Turbinidae were part of the pre-contact Māori diet (Cook, 2009).

Conclusion

In this laboratory report, I compared six examples of species from two families of molluscs, within the bivalves and gastropod order. The six species I am reporting on are divided in half by family. The three bivalve species, classified within the family Veneridae, are Austrovenus stutchburyi, Ruditapes largillierti, and Bassina yatei. The three species I have chosen to report on, Astraea heliotropium, Turbo smaragdus, and Cookia sulcata, are in the gastropod family Turbinidae. The purpose of this report was to describe the distinctions between these species, and to aid in the identification of distinctive characteristics of various species to more easily distinguish them within an archaeological or fossil record. Also, with the previous information one could look into where they lived around the islands of New Zealand, and infer how each may have impacted the archaeological record.  

Work Cited

Beu, A.G. and Raine, J.I., (2009). Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990). GNS Science miscellaneous series, 27.

Cook, S.C. (2009). NZ Coastal Marine Invertebrates; Vol 1. University of Otago. MarineLife.ac.nz (2019).

Helm, M.M., Bourne, N., Lovatelli, A. (2004). Hatchery culture of bivalves: a practical manual (No. 639.2 F3 v. 471). FAO.

Matsukuma, A., Yoosukh, W. 1988: Living Bassina and Placumen (Bivalvia: Veneridae) from the Australasia and the Indo-Pacific. (Studies on the Kawamura Collection (Mollusca) stored in the National Science Museum, Tokyo - V), Saito Ho-on Special Publication p.570.

New Zealand Fisheries. (2019). Frilled Venus Shell (BYA). p. 257-261.

Powell, A.W.B., 1979. New Zealand Mollusca: marine, land, and freshwater shells. Collins.

Vermeij, G.J. and Williams, S.T., (2007). Predation and the geography of opercular thickness in turbinid gastropods. Journal of Molluscan Studies, 73(1), pp.67-73.

Wassilieff, Maggy. (2006). 'Shellfish - Sea snails', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/photograph/8014/cats-eye-in-shell