Cassidulus caribaearum Lamarck, 1801

Souto, Camilla & Martins, Luciana, 2018, Synchrotron micro-CT scanning leads to the discovery of a new genus of morphologically conserved echinoid (Echinodermata: Cassiduloida), Zootaxa 4457 (1) : -

Cassidulus caribaearum Lamarck, 1801

( Figs. 4–6 )

Cassidulus cariboearum Lamarck, 1801: 348 –349.

Rhyncholampas caribaearum — A. Agassiz, 1869:270 –271.

Rhynchopygus caribaearum — A. Agassiz, 1872 –1874:153, 343, pl. 15.

Rhyncholampas cariboearum — H.L. Clark, 1917:106, pl. 144.

Cassidulus caribaearum — Mortensen, 1948a: 205 –210, pls. 2, 11; Gray, 1855:34; Mooi, 1990b: 80.

Cassidulus cariboearum — Kier, 1962: 176 –178, pl. 26.

Type material. Neotype (designated herein): Caribbean Sea, British Virgin Islands, Anegada, Loblolly Bay, 0.5– 1 m, collected by R. Mooi and M. Telford, 01.IV.1986, 26.68 mm TL ( CASIZ 222205).

Neotype choice. In the absence of specimens from the type locality, we chose an adult specimen from one of the few well-studied populations of C. caribaearum . The specimen agrees with the original description of the species and is in great condition (i.e., test is intact and still has spines and pedicellariae).

Comparative material examined. Cassidulus caribaearum Bahamas, TL 17 mm (NHM-UK 87.6.27.7); British Virgin Islands, Anegada, TL 9–30 mm ( CASIZ 112632, 112633, 112637, 112638, 112683 A); and French Antilles, TL 8–20 mm (UF 11786–11788, 11797–11798, 11825, 11892, 11933).

Description. Test oval (TW ca. 85% of TL), lateral edges straight, anterior and posterior margins round; greatest height at apical disc, test height decreases sharply from apical disc to periproct; transverse cross section triangular; oral region concave along the midline of the anterior-posterior axis. Test measurements (TL * TW * TH in mm): 26.68 * 22.65 * 11.71 ( Fig. 4A–B, D–E ).

Apical disc anterior, monobasal, ca. 11% of TL, flat, with four elongated gonopores on disc edge; anterior gonopores closer together, posterior gonopores further apart ( Fig. 4A; 4F , not from N); hydropores abundant and spread across plate. Anterior ocular plates between their adjacent gonopores; posterior ocular plates near distal edge of gonopores 1 and 4.

Petalodium system about 74% of TL. Posterior petals longer than others; anterior petals wider than posterior petals. Anterior petals broad in the middle and narrow distally (not closing), and with bowed columns of respiratory podia. Posterior petals roughly with same width throughout; columns of respiratory podia curved outwards towards test edge. Poriferous zone of petals narrow, pores slightly conjugated; outer pores slightly elongated, inner pores round and smaller than outer. Columns a and b of posterior petals differ by 3–5 pore-pairs (number of respiratory podia: petal I, 27/30; petal V, 27/32), of anterior paired petals differ by 3–4 pore-pairs (number of respiratory podia: petal II, 20/23; petal IV, 20/24), anterior petal is equal (petal III, 25/25 respiratory podia). Primary tubercles present in poriferous zone; 2, sometimes 3 primary tubercles per petal plate. No occluded plates in petals. Ambulacra beyond petals increase 55% in relation to end-petal W; unipores in plates beyond petals: aboral plates wider than long, pores on suture, between adradial edge and middle of plate.

Phyllodes with unipores, with only one column of pores on each half (number of phyllopores: phyllodes 1 and 5, 4/5; phyllodes 2 and 4, 6/6; phyllode 3, 6/5) ( Fig. 4C ). Columns mostly straight, largest W adorally and phyllodes narrow down distally. Buccal pores same size as phyllopores. Four to 6 sphaeridia (109–116 µm L; Fig. 5L ) in large and enclosed pits near buccal pores.

Peristome anterior (34% TL from anterior region), slightly transverse (L 68% of W), pentagonal. Mouth opening in center of peristomial membrane. Bourrelets slightly developed as mounds mostly towards the inside of the peristome.

Naked zone well-developed throughout midline of test on interambulacrum 5 and ambulacrum III, wider anteriorly than posteriorly (W 22% of TW). Deep pits present in oral region, mostly on naked zone. One primary tubercle present on naked zone, adjacent to phyllode 1.

Periproct marginal and transverse (L 70% of W), beyond posterior petals; aboral plates form a prominent lip, oral and lateral plates do not bend inside the periproct ( Fig. 4E; 4I –J , not from N). Periproctal membrane with 2 rows of 5–6 medium- to large-sized plates; smaller plates scattered in aboral region near anus ( Fig. 4I –J , not from N). Anus opening aborally, on center of periproctal membrane and surrounded by elongated papillae.

Primary tubercles perforate and slightly crenulate. Oral primary tubercles with mamelon displaced in the opposite direction of the spine (usually anteriorly from center of bosses) and 2.25x as large as aboral tubercles. Aboral spines short, straight, apex thicker than base, shaft serrated ( Fig. 5C ); bourrelet spines curved, shaft serrated, base short ( Fig. 5D ); oral spines long, straight, thicker at the base than at the apex, shaft mostly smooth ( Fig. 5E ; not from N); spines on lip above periproct thin, straight, intermediate in size between oral and aboral spines, shaft slightly serrated on both extremities. Miliary spines abundant, short, straight, thickness uniform, tip crown-shaped, shaft serrated ( Fig. 5F , not from N).

Periproctal and peristomial membranes with small ossicles. Triphyllous pedicellariae small and apparently abundant near aboral ambulacra. Valves short and broad (45–56 µm L; Fig. 6A–B ) with delicate teeth along whole blade margin. Ophicephalous pedicellariae small and rare. Valves (135–181 µm L; Fig. 6C–D ) with coarse teeth along whole blade margin (open row, U-shaped). Hinge broad, handles conspicuous. Two types of tridentate pedicellariae found. Large type found near posterior petals and periproct; valves (302–407 µm L; Fig. 6E–H ) broad and robust; blade with thin teeth along whole margin, teeth on distal margin numerous and very long; region between blade and basal region wide, basal region tall; stalk (494–553 µm L; Fig. 5G ) robust, proximal region thicker than distal region and with pointy upward projections ( Fig. 5H ), no neck present. Small type found around apical disc where embryos and young ( Fig. 5A–B ) are; valves (228–302 µm L; Fig. 6I –L ) broad; blade with coarse teeth along whole margin, teeth on distal margin larger; region between blade and basal region narrow, basal region short and spineless; stalk (610–767 [broken] µm L; Fig. 5I ) long and thin, base thicker than apex, stereom thin and intricate ( Fig. 5J ), neck present.

Additional information based on comparative material and literature. Posterior region of apical disc slightly bulged towards interambulacrum. Oral plates beyond petals about 1.15–1.60x longer than wide, pores near the distal edge of plate suture. Plates on phyllodes sometimes unequal in size and shape; pyrinoid plates not present. Phyllopores usually aligned in a uniform column. Ambulacral basicoronal plates pierced by buccal pore and one per ambulacrum also pierced by a phyllopore in the sequence a, b, a, b, b from phyllode I to V ( Fig. 4H ). Columns a and b of interambulacrum 5 with 6–7 plates between basicoronal plate and base of periproct and 3 (rarely 4) until adapical region of periproct (i.e., periproct is framed by 4 [rarely 3] plates on each side). Interambulacral basicoronal plates 1 and 4 narrower than others, 5 the broadest, 2 and 3 intermediate in size. Second and third oral plates on interambulacrum 5 are much longer than wide. Periproct framed adorally by plates 5.a.6 (or 5.a.7) and 5.b.7, and adapically by plates 5.a.10 (or 5.a.9) and 5.b.10.

Gastric caecum highly reduced ( Ziegler et al., 2008). Anterior stomach located in ambulacrum III, where it joins the short esophagus, and in interambulacrum 3; a cluster of 4–6 smooth, finger-like pouches at the junction of esophagus and anterior stomach, and further subdivided into two smaller clusters directed laterally towards interambulacra 2 and 3 ( Ziegler et al., 2010). Color in vivo: white ( Kier, 1975).

Intraspecific variability. Besides the difference in the number of plates on oral interambulacrum 5, other differences were observed between specimens. For instance, the difference in the number of respiratory podia between the columns a and b of anterior paired petals varies from 2–4 pore-pairs. Also, the number of phyllopores varies from 4–5 in phyllodes I, III and V, and from 5–7 in phyllodes II and IV; and although most specimens have deep pits in the naked region, a few others have shallow and small pits.

Bathymetric and geographic distribution. Cassidulus caribaearum has been recorded in Belize, the British Virgin Islands, Jamaica, Mexico, Panama and Puerto Rico ( Lamarck, 1801; Gladfelter, 1978; Kier, 1975; Tzompantzi et al., 1999; Alvarado et al., 2008; Rodríguez-Barreras et al., 2012), Bahamas and French Antilles (extended herein). The NHM-UK database holds occurrences from Antigua and Barbuda. Occurrence of the species in the Dominican Republic has been indicated by Alvarado (2011), but we have not been able to find the original reference for the occurrence nor a record in museum databases.

This species occurs in shallow water, up to 18 m of depth ( Mooi, 1990b; extended herein). A. Agassiz’s ( 1872 – 1874, p. 343) record of specimens living at 106 fathoms (ca. 194 m) of depth is probably wrong.

Natural history notes. Even though C. caribaearum was described more than 200 years ago and is fairly welldistributed in shallow Caribbean waters, information about this species is still scarce. The specimens analyzed herein were collected from 10–100 mm beneath the surface of the sediment, which was composed of clean calcareous sand. This specific population migrates with changes in season and the density of individuals varies between 5–25 individuals/m2 ( Gladfelter, 1978).

Some cassiduloids are known to brood their young ( Mortensen, 1948a), sometimes in brooding pouches or among the aboral spines, as is the case for C. caribaearum . The neotype described herein has several embryos and young in the aboral region (see dark yellow patch around apical disc on Fig. 4A ). Gladfelter (1978) suggested that fertilization in this species may be internal and he also did not rule out the possibility of parthenogenesis; both hypotheses remain to be tested. Sexual dimorphism in gonopore size is not as apparent as in other cassiduloids (e.g., Neolampas rostellata A. Agassiz, 1869 ) but because of the presence of embryos on the test, the neotype is most likely a female. Sexual maturity was observed in individuals larger than 10 mm in TL.

See Gladfelter (1978) and Telford & Mooi (1996) for additional information on the natural history of C. caribaearum .

Figures

FIGURE 4. Cassidulus caribaearum Lamarck, 1801 (CASIZ 222205 [neotype] [A–E]; CASIZ 112683B [F–G, I–J]; CASIZ 112683A [H]): photos of test in (A) aboral and (B) oral view, (C) detail of peristome and phyllodes, and test in (D) side and (E) posterior view; SRµCT-based volume renderings of apical disc in (F) external and (G) internal view (arrows indicate calcareous ridges beneath madreporic plate), (H) of peristome in internal view, and of periproct in (I) internal and (J) external view. Scale bars: A–E, 5 mm; F–J, 1 mm.

FIGURE 5. Cassidulus caribaearum Lamarck, 1801 (CASIZ 222205 [neotype] [A–D, I–L]; CASIZ 112638 [E–G, M]), SEM images: (A–B) juveniles attached to the test; (C) aboral, (D) bourrelet, (E) oral and (F) miliary spines; stalk of (G) large tridentate pedicellariae (detail of projections in H), (I) small tridentate pedicellariae (detail of stereom in J), and of (K) ophicephalous pedicellariae; (L) sphaeridium; and (M) young spine. Scale bars: A–B, M, 100 µm; C–I, 200 µm; K–L, 50 µm.

FIGURE 6. Cassidulus caribaearum Lamarck, 1801 (CASIZ 222205 [neotype] [B–E, J–L]; CASIZ 112638 [A, F–I]), SEM images: valves of (A–B) triphyllous pedicellariae, (C–D) ophicephalous pedicellariae, (E–G) large tridentate pedicellariae ([H] detail of valve head), and (I–K) small tridentate pedicellariae ([L] detail of valve head). Scale bars: A–B, 15 µm; C–D, H, L, 30 µm; E–G, I–K, 100 µm.