Table 2. Morphometric analysis of Aphrocallistes vastus.

							% of inhalant surface		Water velocity (µm s−1)		Head loss (ΔH, µm)
Region	Inner Diameter (Di, µm)		Path Length (Li, µm)		Dist. from Inhalant surface (µm)	Cross section Area (mm2)	A. Vastus	Std. Sponge	A. Vastus	Std. Sponge	A. Vastus	Std. Sponge	% of total	Relative head (µm)
Ostia	4	a	0.500	b	0.0000	4.7	26	30	1,107	400	173	37	8.3	1902.7
Subdermal space	90	c	82	d	0.0085	16.7	93	95	309		15		0.7	1887.9
Large incurrent canal	366	e	2,000	f	1.4043	3.1	17	10	1,673	120	118	120	5.7	1769.9
Medium incurrent canals	182	e1	529	f1	35.2553	4.6	26		1,123		84		4.1	1685.7
Small incurrent canals	59	e2	237	f2	44.2035	5.8	32		897		289		13.9	1396.8
Prosopyles	2.1	g	0.500	h	48.2081	275.1	1524	207	19	60	10	115	0.5	1387.2
Pre-collar space	2.0	i	1.650	j	48.2166	161.0	892	3,500	32	3.4	62		3.0	1324.9
Glycocalyx mesh pores	0.045	k	0.010	l	48.2445	251.3	1392		21		455		21.9	870.3
Collar slit	0.119	m	0.070	n	48.2447	722.0	4000	5,600	7	2.1	168	122	8.1	702.4
Glycocalyx mesh pores	0.045	k	0.010	l	48.2459	251.3	1392		21		455		21.9	247.9
Post-collar space	2.0	i	1.650	j	48.2460	161.0	892		32		62		3.0	185.5
Collar apertures	2.0	o	0.500	p	48.2739	401.0	2222	810	13	15	8		0.4	177.9
Chamber	56	q	56	r	48.2824	439.3	2433		12		1		0.0	176.9
Apopyle	26	s	2	t	49.2307	204.3	1132	420	25	29	0		0.0	176.6
Small excurrent canals	218	u1	118	v1	49.2646	1.1	6		4,706		55		2.6	121.7
Large excurrent canals	405	u	2,840	v	51.2545	3.8	21	3	1,363	4,000	111	120	5.4	10.5
Subatrial space	80	w	40	x	99.3230	14.4	80		358		11		0.5	0.0
Atrial cavity	62,000		279,000		100.0000									0.0
Osculum	45,000	y	500	z	4822.2	0.5	3					157
Total			5908							2,075	671
Chambers per mm3							1,876	12,000
Collars per chamber							260	95
Microvilli per collar							38	28

Numbers represent means of 3–50 measurements from 1–8 samples. Percent of the inhalant surface, water velocity, and head losses (ΔH) at each region are compared with the ‘standard sponge’ of Riisgård et al. [30] and Larsen and Riisgård [29] (blue font) which are calculated using measurements made by Reiswig (1975). Regions and their dimensions (e.g., diameter and length) are identified by letters repeated in Figures 6 and 7. The sum of consecutive path lengths gives the distance (µm) from the surface of the sponge. The water velocity at each region is calculated for 10°C water and an excurrent velocity of 1 cm s⁻¹ measured at the osculum, corresponding to a specific pumping rate of 3.1 mL (mL sponge)⁻¹ min⁻¹ (see text and Riisgård et al., 1993). ‘Atrial cavity’ and ‘Osculum’ pertain to the average size of the sponges used in the tank experiment (Table 1).

The cross sectional area, water velocity and head loss of the passages through the aquiferous system in 100 ul (100 mm³) pieces.