Alloeocomatella Messing 1995

Alloeocomatella Messing, 1995

Table 1, Fig. 1 A–D, Fig. 2

Type species. Alloeocomatella polycladia Messing, 1995a.

Other included taxa (1). Comissia pectinifer AH Clark, 1911a.

Description. Mouth excentric in fully developed individuals; up to 30 arms; centrodorsal always welldeveloped, rounded pentagonal, and with cirri (Figs. 1 B); all brachitaxes of 2 ossicles united by synarthry; first syzygy at 3+4 on arms arising from IBr (and IIBr when 20 or fewer arms present); arms arising from IIBr and IIIBr (specimens with>20 arms) with first syzygies at 1+2 and/or 3+4 (rarely 1+2 alone); distal intersyzygial interval usually 3; distalmost pinnule comb on P4–P8; comb of>20 (up to 39) tall, narrow, triangular, teeth confluent with outer edge of pinnule; comb not tapering significantly distally (Fig. 1 C).

Distribution. Tropical Indo-western Pacific from northern Australia west to Chuuk Atoll and New Caledonia, east to the Maldive Islands, and north to Okinawa and Guam (Kirkendale and Messing 2003; Messing 1995a, 1998b; Meyer 1986; Pilcher & Messing 2001). Depth range: 3 to at least 25 m (one record of 100 m [AH Clark 1931]). Known definitely from 6–18 m (Alloeocomatella polycladia) and 3–23 m (A. pectinifera) (Messing 1995a).

Molecular results. Specimens identified as Alloeocomatella polycladia and A. pectinifera return as three distinct clades in parsimony and likelihood analysis (Fig. 2), with a minimum of 5.7% uncorrected COI distance among them. Noticeable morphological variation was observed for Alloeocomatella polycladia (e.g., size; numbers of arms, cirri, cirrals, and rows of cirri, distal intersyzygial intervals, presence/absence of distal spinose margins on arms), yet intra specific difference for COI was less than 0.6% among specimens collected at Lizard Island and Papua New Guinea (n=4). In contrast, little morphological variation has been recorded for Alloeocomatella pectinifera, yet there was up to 7% COI divergence among specimens from only Madang, Papua New Guinea. This high variation could suggest two species of Alloeocomatella pectinifera. Two distinct A. pectinifera clades; A. pectinifera type A (2.3–4.3% uncorrected intra specific divergence (n=6)) and A. pectinifera type B (one specimen only) were recovered in the phylogenetic analyses. The type locality for A. pectinifera is Christmas Island, an Australian territory in the Indian Ocean near Indonesia. Until samples are examined from there, the question of whether A. pectinifera represents one versus more species must be left unresolved.

Remarks. Alloeocomatella includes two species that co-occur and are widely-distributed in the Indo-western Pacific. Both are easily distinguished from other comatulids in the field by their rich red, red-orange or red-purple color (Fig. 1 A, D), generally softer consistency, greater flexibility, and smoother texture (due to fewer and weaker pinnule spines). They also array pinnules in a single pinnate plane, like barbs on a feather (Fig. 1 D), unlike the tetrad arrangement characteristic of most confamilials. Both species are cryptic during the day. At night, A. pectinifera keeps its centrodorsal concealed but extends 4–8 of its ten arms usually upward and in parallel (Fig. 1 A). Arm length reaches 50 cm, the longest of any extant crinoid. A. polycladia has up to 30 arms; specimens with ~20 or fewer arms remain concealed at night with several arms extended; larger specimens perch completely in the open (Messing 1995a). Following collection, A. polycladia curls its arm tips (Fig. 1 D), while A. pectinifera arms remain extended and straight. We have not yet found any morphological distinctions between Alloeocomatella pectinifera types A and B.