Nacospatangus altus
Creators: name: Arachchige, Gayashan M.
name: Jayakody, Sevvandi
name: Mooi, Rich
name: Kroh, Andreas
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Echinoidea
Spatangoida
Maretiidae
Nacospatangus
Nacospatangus altus

description: Nacospatangus altus (A. Agassiz, 1864)
Figures 74–75
1864 Maretia alta A. Agassiz: p. 360.
1951 Pseudomaretia alta (A. Agassiz).—Mortensen: p. 58–62; pl. 3: figs. 12–14, 16–20; pl. 46: figs. 1–6, 8–11, 13, 19, 20.
Material studied. Five denuded specimens: WUSL/EI/82, EI/83, EI/116, and EI/117, from Kamburugamuwa, and WUSL/EI/115, from Mount Lavinia, Sri Lanka.
Description.
Shape and size —Test thin and fragile; medium-sized, 32.7–46.95 mm TL; width 73–80% TL, greatest width about halfway along length; outline of anterior end gently curved with very inconspicuous anterior notch; TH 42–45% TL, highest point along posterior interambulacrum 5 which forms a sharp keel; posterior end obliquely truncated in lateral view; oral side flat but sternum rises into a conspicuous keel at its posterior end; ambitus sharply curved from aboral to oral surface.
Apical system —Ethmolytic, with three gonopores (no gonopore in genital plate 2); posterior pore pair larger than anterior gonopore; madreporite not conspicuously extending beyond posterior oculars; situated anterior of centre, c. 33% TL (SD=1, N=6) from anterior margin.
Ambulacra —Ambulacrum III narrow, very slightly sunken; paired petals with unequal poriferous zones, nearly closed, pores in single pore pair equal in size, slightly pointed at inner ends, pore series converging distally; adapical pore pairs rudimentary in both anterior and posterior paired petals; poriferous zones of anterior paired petals highly unequal, in anterior paired petal, posterior poriferous zone (petal IIa, IVb) usually 7–9 pore pairs longer than anterior poriferous zone (petal IIb, IVa); in posterior paired petals (petals I, V), length difference not as pronounced and posterior poriferous zones (petal Ia, Vb) usually a single pore pair shorter than anterior ones (petal Ib, Va) (however, largest examined specimen [WUSL/EI/82] shows equal pore pair numbers in both anterior and posterior poriferous zones); length of rudimentary area of anterior poriferous zones (petal IIb, IVa) greater than posterior poriferous zones (petal IIa, IVb) of anterior paired petal, c. 17% and 3% TL respectively; length of rudimentary area of anterior (Ib, Va) and posterior poriferous zones (petal Ia, Vb) of posterior paired petal nearly equal, c. 8% TL respectively.
Tuberculation —Aboral interambulacra uniformly and densely covered by small secondary tubercles, except for a few enlarged primary tubercles in interambulacra 1, 2, 3, and 4; aboral interambulacrum 5 without enlarged primary tubercles; in aboral interambulacra 2 and 3, many enlarged primary tubercles present along adjoining anterior ambulacrum; these tubercles without sunken areoles; two series (or exceptionally three) of enlarged tubercles along interambulacra 1 and 4 on each side starting anteriorly from very close to posterior poriferous zones of anterior paired petals, first series consists of 3–4 and rarely 5 enlarged primary tubercles just aboral to ambitus (Fig. 74C, D); second series 1–2 tubercles just above first series; rarely third series with a single enlarged primary tubercle; these tubercles non-crenulate with deeply sunken areoles; oral interambulacra with non-crenulate primary tubercles, mamelon of tubercles eccentric; these primary tubercles smaller than tubercles on aboral interambulacra 1 and 4, and larger than tubercles on aboral interambulacra 2 and 3; tubercles on adoral interambulacrum 5 smaller than other tubercles on oral interambulacra; larger tubercles present along adjoining ambulacra.
Plastron —Narrow, width c. 16% TL (SD=0.43, N=6); sternal plates tuberculate except for small part along anterior end; sternal plates forming conspicuous median keel towards posterior end; labrum arrow, slightly elevated at peristome with narrow posterior prolongation.
Fasciole —Subanal fasciole well-developed, heart-shaped, adoral end pointed, adapical fasciole following lower edge of periproctal cavity; height of subanal fasciole approximately 21% TL (SD=1.1, N=6) and width approximately 28% TL (SD=0.7, N=6); usually encloses three pore pairs on each side, exceptionally, four pore pairs in each side of largest specimens examined (WUSL/EI/82); no anal branches.
Peristome —D-shaped; oblique; moderately large, length 9–12% TL, width 15–17% TL; 24–25% TL from anterior margin.
Periproct —Large, length 12–19% TL, width 14–19% TL; fully visible in oral view..
Geographic range. Indo-West Pacific, from Islands of West Indian Ocean (Clark 1925a), Mauritius (De Loriol 1883), Sri Lanka (Clark 1915), Bay of Bengal (Koehler 1914), East Indies (de Meijere 1904) to Philippine Islands (Mortensen 1948e; Mortensen 1951) and China & South Japan (Agassiz 1872).
Bathymetric range. 1.5–204 m (Mortensen 1951).
Observed occurrence in Sri Lanka. Specimens were collected from sand patches between patch reefs on the western and southern coasts of Sri Lanka, at a depth of 20–30 m (Fig. 75).
Remarks. The number of the distal pore pairs in the anterior series of the anterior paired petals is variable. Out of six specimens, only one (WUSL/EI/127, 38.0 mm TL) has 5 distal pore pairs, while four specimens have 8 distal pore pairs and the largest examined specimen has 9. Mortensen (1951: 59) observed 5–6 distal pore pairs in the anterior series of the anterior petals in his specimens, even though he had examined specimens up to a size of 54 mm. Likewise, number of enlarge primary tubercles is variable: some of the examined materials (WUSL/EI/116, 34.2 mm TL; WUSL/EI/83, 37.3 mm TL; WUSL/EI/127, 37.95 mm TL) and (WUSL/EI/82, 46.95 mm TL) have seven and eight large tubercles in interambulacrum 4 respectively. This differs from Mortensen’s (1951) observations. These features suggest intraspecific variation and can thus only be used in conjunction with the additional characters listed above.
description: Published as part of Arachchige, Gayashan M., Jayakody, Sevvandi, Mooi, Rich & Kroh, Andreas, 2019, Taxonomy and distribution of irregular echinoids (Echinoidea: Irregularia) from Sri Lanka, pp. 1-100 in Zootaxa 4541 (1) on pages 86-89, DOI: 10.11646/zootaxa.4541.1.1, http://zenodo.org/record/2617460