214 
THE CORAL TRIANGLE: HEARST BIODIVERSITY EXPEDITION 
cutting up plant material or sessile organisms that form the primary food sources of these echi- 
noids. 
Less familiar, usually burrowing echinoids with a dense, almost hair-like covering of thin, 
sometimes very short spines are placed in a monophyletic group known as the Irregularia (Kroh 
and Smith 2011). The term “irregular” refers to the fact that the anus is no longer found at the top 
of the animal, but at the posterior end, giving these forms a secondarily derived anterior-posterior 
axis that disturbs the “regular” pentaradial symmetry of most other urchins. Among these, the heart 
urchins (spatangoids) can be sti'ongly bilateral, capable only of moving forward in substrates rang¬ 
ing from soft muds to relatively clean sands of varying particle size ranges. Being sediment-swal¬ 
lowers, they lack the Aristotle’s lantern. However, other IiTegulai'ia such as sand dollars, sea bis- 
euits, sea pancakes, pea urchins, and keyhole urchins (all clypeasteroids) retain the lantern into 
adulthood. Sand dollar-like taxa have extremely miniaturized spines that they use for locomotion 
through relatively clean, fine sands. Their tube feet are likewise mmiaturized, adapted to handling 
individual, nutrient-bearing particles that are passed to the mouth, ingested, and cmshed by the 
lantern. A much rarer group of IiTegularia, lamp urchins (cassiduloids and echinolampadoids), once 
dominated in the Mesozoic and early Cenozoic. These are cryptie forms, “nestling” in coral mbble 
or burrowing into coarser sands. Although seldom seen today, several unusual lamp urchins are 
known from the Philippines. 
Echinoids can be found in every oeean, from the upper intertidal to the deepest parts of the 
abyss. Almost every major eehinoid clade contains deep-sea forms, and many of these are repre¬ 
sented in the Philippines. However, coral reefs and soft substrates in lagoons and among the coral 
cover itself hai'bor the majority of Philippine eehinoid taxa. Sea urchins, particularly the “regular” 
forms that ai*e important herbivores, are crueial to the ecology of reefs (e.g. Ostrander 1999, Bell- 
wood et al. 2004), often filling roles left vacant by local extirpation of fish speeies. It is also becom¬ 
ing increasingly clear that bathymetry has important effeets on the overall significance of echinoids 
in reef ecology (e.g. Hughes 1996), making it crucial that accurate depth data are recorded for all 
species. In addition, echinoids are themselves important food sources for fish and cmstaceans, not 
only as adults, but as larvae. 
Sea urchins exert significant influence on the environments in which they live, in shallow 
water as well as at extreme depths. For example, the activities of large numbers of subtidal “regu¬ 
lar” urchins can greatly alter the physical environment, particularly through bioerosion. Camaro- 
dont “regular” urchins such as Echinometra (Fig. 1 A) alter their environment by actually chewing 
into the coral rock in which they live (Hiratsuka and Uehara 2007). Interestingly, juvenile Echi¬ 
nometra were seldom found in burrows or channels of their own eonstniction, but were instead 
eommonly ensconced in the empty shells of dead barnacles (Fig. IB). Our shallow water work in 
the Verde Island Passage provided abundant evidenee for the environment-altering activities of 
these urehins (Figs. 1C, D). 
Urchins themselves support a wide variety of benthie invertebrates that find shelter and some¬ 
times food among the spines. Certain species of fish also use the spines of larger ui*chins sueh as 
Diadema for protection. Large species of deep-sea heart urchins can act as hosts for internal 
bivalve commensals, and as a substrate for different species of brittlestars (see below). Cidaroid 
slate pencil urchins actually encomage settlement of other organisms onto their large spines. These 
urchins frequently can*y around a rich epizoic community made up of bryozoans, sponges, bama- 
eles, polychaetes, and other groups, particularly in the deep sea. As such, a single specimen of 
deep-sea urchin can represent a mobile, highly diverse sampling of the community all on its own. 
In addition to their ecological importance, some urchins can inflict injury if not approached 
with respeet. Forms such as the echinothurioids have a flexible test in whieh the eomponent stere- 
